3rd International Workshop on Hydrogen and Fuel Cells

in 10th International Summer School on Advanced Studies of Polymer Electrolyte Fuel Cells

Yokohama National University, August 20th – 25th, 2017

1

Program 3rd International Workshop on Hydrogen and Fuel Cell

1 Lecture of cutting edge 5 Chemical design of nanomaterials for energy and environmental applications

Yoshiyuki Kuroda, Yokohama National University

25 HySA system 1kWe CHP system Cordellia Sita, University of the Western Cape

2 Poster session P1 LONG-TERM STORAGE AND DISTRIBUTION OF HYDROGEN WITH IRON- 35

BASED OXYGEN CARRIER MATERIALS

Sebastian Bock, Graz University of Technology

P2 DETECTION OF CRITICAL CONDITIONS IN POLYMER ELECTROLYTE 37

FUEL CELLS USING IMPEDANCE SPECTROSCOPY AND TOTAL

HARMONIC DISTORTION ANALYSIS

Kurt Mayer, Graz University of Technology

P3 INFLUENCE OF FEED GAS COMPOSITION ON REDUCTION REACTION 39

FOR FIXED BED STEAM - IRON PROCESS

Verena Martschitsch, Graz University of Technology

P4 ANODE CATALYSTS FOR THE ALKALINE DEFC TESTED IN A SINGLE 41

CELL USING POLYBENZIMIDAZOLE MEMBRANE

Johanna Ranninger, Graz University of Technology

P5 FUNCTIONALIZED CATALYSTS FOR THE OXYGEN REDUCTION 43

REACTION IN HIGH TEMPERATURE PEM FUEL CELLS

Katharina Kocher, Graz University of Technology

P6 EXERGY ANALYSIS OF A POLYMER ELECTROLYTE FUEL CELL (PEFC) 45

Turgay Koroglu, Graz University of Technology

P7 PERFORMANCE ANALYSIS OF STAND-ALONE HT-PEMFCS BASED 47

TRIGENERATION SYSTEM FOR RESIDENTIAL APPLICATION

Suthida Authayanun, Srinakharinwirot University

P8 A research about numerical analysis of gas-liquid two-phase flow in the Gas 49

Channel considering of the GDL

Wang Lida, Yokohama National University

2

P9 DEVELOPMENT OF CONDUCTIVE OXIDE AS CATALYST SUPPORT OF 51

PRECIOUS -METAL-FREE OXIDE BASED CATHODE FOR PEFCS

Hikaru Igarashi, Yokohama National University

P10 EFFECTS OF ION EXCHANGE CAPACITY ON TOLUENE PERMEABILITY 53

IN PROTON EXCHANGE MEMBRANE

Keisuke Tanimoto, Yokohama National University

P11 ELECTROCONDUCTIVE TITANIUM OXIDE AS SUPPORT MATERIAL OF 55

OXYGEN EVOLUTION ELECTRODE IN ACIDIC ELECTROLYTE

Masayuki Nagai, Yokohama National University

P12 MORPHOLOGY-CONTROLLED TITANIUM OXIDE NANO-PARTICLES AS 57

SUPPORTS OF CATHODE CATALYSTS FOR POLYMER ELECTROLYTE

FUEL CELLS

Yongbin Ma, Yokohama National University

P13 CATALITIC ACTIVITY AND DURABILITY FOR OXYGEN EVOLUTION ON 59

La-Ni-O/Ni FOR ALKALINE WATER ELECTROLYSIS UNDER POTENTIAL

CYCLING

Yudai Tsukada, Yokohama National University

P14 EFFECT OF CONDUCTIVE SUBSTANCE ADDITION TO NB-DOPED 61

TITANIUM OXIDES AS NON-PLATINUM OXIDE-BASED CATHODES FOR

PEFC

Tsubasa Tokai, Yokohama National University

P15 MODEL ELECTRODE OF OXYGEN REDUCTION CATALYST FOR PEFCS 63

BASED ON TITANIUM OXIDE BY ARC PLASMA DEPOSITION

Kaoru Nagano, Yokohama National University

P16 A VISUALIZATION TECHNIQUE DEVELOPMENT FOR UNSTEADY 65

HYDROGEN CONCENTRATION DISTRIBUTION IN POROUS MATERIALS

Konosuke Watanabe, Yokohama National University

P17 MEASUREMENT OF TEMPERATURE DISTRIBUTIONS OF A MICRO- 67

TUBULAR SOEC DURING H2O/CO2 CO-ELECTROLYSIS

Atsushi Maeda, Yokohama National University

P18 CONJUGATE ANALYSIS OF HEAT-SPECIES-CHARGE TRANSPORT AND 69

CATALYST OXIDATION IN PEMFC

Satoshi Nishimura, Yokohama National University

P19 IN-SITU MEASUREMENTS OF HUMIDITY IN A PEMFC CHANNEL USING 71

MEMS SENSORS

Noriyoshi Hasegawa, Yokohama National University

3

P20 ANALYSIS OF VISUALIZATION ABOUT EFFECT OF GDL 73

CONFIGURATION ON WATER DISTRIBUTION INSIDE PEFC

Yusuke Tamada, Yokohama National University

P21 EXTENSION OF SPECIFIC SURFACE AREA OF IrO2-Ta2O5/Ti ANODE 75

CATALYST

Kohei Maniwa, Yokohama National University

P22 RELATIONSHIP BETWEEN AMOUNT OF LITHIUM DOPED AND OER OF 77

LIXNI2-XO2/NI FOR ALKALINE WATER ELECTROLYSIS

Xu Yao, Yokohama National University

P23 ELECTRODE POTENTIAL MEASUREMENT IN POLYMER ELECTROLYTE 79

MEMBRANE WATER ELECTROLYZER

Naoto Morita, Yokohama National University

P24 PREPARATION OF POROUS NB-DOPED TITANIUM OXIDE USING A 81

COLLOIDAL CRYSTAL TEMPLATE FOR CATALYST SUPPORTS

Hirotaka Kajima, Yokohama National University

4

Abstracts of

Lecture of cutting edge

4

5

10th International Summer School 2017/8/23on Advanced Studies of Polymer Electrolyte Fuel Cells

Chemical design of nanomaterials for energy and environmental applications

Yoshiyuki Kuroda

Yokohama National University

1

Facing problems in 21st century

Population Global warming issueEnvironmental pollution

Energy/resource problem Healthcare2

6

Technologies to solve these problems

Global warming Environmental pollutionPopulation issue

Green catalyst

PhotcatalystPurificationFuel cell

H2 productionHealthcareNanomedicineEnergy/resource problem

Material chemistry is important to support 3 these technologies.

Designability of materialsScale of structure

Crystal structure Nanostructure Morphology

• Nanostructures have significant influences on the properties.

• Materials must be designed in all length scales.Nanospace crystals

4

7

Catalysis

Nanospace materialsNanoporous materials

• Materials with ordered pores• High surface area• Molecular sieving effect• Unique nanoconfinement effects

O

H2O2

Separation membrane Drug delivery system5

Nanospace materialsIntercalation materials

• Layered materials and some lithium ion insertion materials

• Atomic scale nanospace in which guest ions are strongly trapped

• Structure-related properties are often observed.

B–A–

×

Selective ion exchange Lithium ion battery6

8

Today’s topicsMn-based mixed metal oxides (MMOs)with controlled morphology, structure, and composition

Mn-based materials include diverse nanospace materialswith potential applications for energy and environmental issues.

• Use of templating effect of metal cations under strictly controlled concentration of water

• Lithium ion recovery• Lithium ion battery• Selective oxidation catalysis

7

Mn-based mixed metal oxidesStructures and properties depend on M and MMnO2 synthetic route.[1]

1D tunnel structure 2D layered structure 3D spinel structure

Applications• Pseudo-capacitors• Primary battery• Ion exchangers• Secondary battery• Ion conductors• Oxidation catalysts

• Electrocatalysts8 [1] Q. Feng et al., J. Mater. Chem. 1999, 9, 319.

9

A concept for low-temp. synthesis

Reduction–recrystallization concept

CoCl2 aq. High OER/ORR activity!!

NaBH4

r.t.amorphous MnO2 CoMn2O4

But, we could not reproduce the synthesis...9 [1] F. Cheng et al., Nat. Chem. 2010, 3, 79.

Mechanism for low-temp. synthesis

Amorphous precursor can reduce activation energy for the phase transition.

10 [1] F. Cheng et al., Nat. Chem. 2010, 3, 79.

10

Synthetic conditions and structures

2D 1D 3DStructure layered structure tunnel structure spinel structureSynthetic Low temp. Moderate temp. High temp.temp. r.t.–100 °C 100–150 °C 150–200°C

Space Wide Medium Very narrow

Mainly hydrated Dehydrated Template Hydrated cation cation cationIt is difficult to control the morphology of spinelsbecause of the relatively high synthetic temperature.11

Our strategy for low-temp. synthesisPrecursory oxide

The amorphous MnO2 is possibly randomly stacked layered oxides.

or⇒ Start from molecular precursor

MnO4–

Dehydration of template cationsMn+ is hydrated in water.

[M(H2O)6]n+

or Template must be dehydrated to form spinel structure with narrow space.

⇒ Use of organic solvent for dehydration of template cations12

11

Unique precursor molecule

TBABr

KMnO4 TBAMnO4[1]

TBA = tetrabutylammonium

• Easy to handle • Highly soluble in organic • Low cost solvents• Less soluble or insoluble • Self-decomposition

in organic solvents Explosive if organic moiety has unsaturated bonds[1]

13 [1] S. L. Suib et al., J. Phys. Chem. B 1999, 103, 7416.

New synthetic method for LiMn2O4Solvent & reductant

86 °C

30 min

• Mixed metal oxides were directly synthesized from molecular precursor.

• Li–Mn spinel is obtained at extremely low TBAMnO4 temperature (cf. usually at 180 °C)

• Crystal structure is controllable by hydration of template cation (Li+).

14

12

Amorphous Li–Mn–O (before reflux)Amorphous MnO2

[1]layer structure

• No Li+ is incorporated. slight crystallinity (Li+ was not used for its

synthesis)• Trace peaks due to layered

structure were observed.amo. MnO2[1]

Amorphous Li–Mn–O• Li0.401Mn0.919O2amo. Li–Mn–O

(Prepared in the presence of Li+)

• Only broad and weak peaks were observed.

Truly amorphous Li–Mn–O precursor was obtained by excluding water.

15 [1] F. Cheng et al., Nat. Chem. 2010, 3, 79.

Growth of spinel phase (after reflux)XRD with varied reflux period Change in crystallite size

H2O/Li=0

• Li–Mn–O crystallizes upon reflux.

• Particle size increases along with the reflux period.⇒ Nanoparticles are obtained by a short-time reflux.16

13

The smallest nanoparticle (H2O/Li = 0, 30 min)

TEM images Size distribution

ave.2.55 nm

XRD pattern• The smallest Li–Mn spinel

D111 = 2.3 nm nanoparticle• Li0.825(Mn0.966Li0.034)2O4• BET surface area: 386 m2/gLiMn2O4 (spinel)

17

Effect of hydration of Li+

Reflux: 3 h Layer2.4 Å

H2O/Li=500Layer

*Interlayer H2O is 200omitted for clarity20 birnessite

10

0Li-birnessite 1.2 Å

LiMn2O4

spinelAt low temperature, the dehydration of Li+ is the most significant barrier to form the spinel structure.18

14

Effect of template cationsCo2+ was used as a template TEM image

H2O/Co= 60

30

0.95 nm

20

6When Co2+ is used, 1D tunnel structure[1] is also formed under appropriate H2O/Co ratio.0

[1] Characterized according to S. L. Suib et 19 al., Chem. Mater. 2004, 16, 4296.

Overview of the template effect

*Ionic potential = Z/r, where Z = valence and r = ionic radius, an indicator of electrostatic interaction• Spinel is obtained from dehydrated template.• 2D and 1D structures are obtained from hydrated template and ionic

20 potential is a possible control factor for the structures.

Template Valence (Z) /-

ionic radius (r) /Å

ionic potential*/Å–1

Product from hydrated template

Product from dehydrated template

TBA+ 1 4.94 0.20 amorphous amorphousK+ 1 1.33 0.75 2D layered amorphousBa2+ 2 1.35 1.48 insoluble -Li+ 1 0.60 1.67 2D layered 3D spinelSr2+ 2 1.13 1.77 amorphous insoluble

Ca2+ 2 0.99 2.02 amorphous amorphous

Mn2+ 2 0.80 2.50 amorphous -

La3+ 3 1.15 2.61 amorphous insolubleZn2+ 2 0.74 2.70 3D spinel 3D spinelCo2+ 2 0.72 2.78 1D tunnel 3D spinelNi2+ 2 0.70 2.86 1D tunnel insolubleMg2+ 2 0.65 3.08 1D tunnel 3D spinel

MnxOyn– MnxOyn–

MnxOyn–O

O H

2

H

–

n–

15

+

Formation mechanism

TBA MnO4 without H2OMClx2-propanol small templateH2O

with H2O

Case: small ionic potential Case: large ionic potential

MnxOyn– MnxOyn MnxOyn–

MnxOyn–

H2H2O H2O 2OMnxOyn–

H2OLi+ 2OMg2MnxOyn–

H2 H2OMnH O xOyn–MnxOyn–MnxOyn–MnxOy

21

Summary of the syntheses

This method allows production of very fine nanoparticles with controlled crystal structures.

22

16

Applications of Mn-based MMO nanoparticles

• Li+ recovery with Li–Mn spinel nanoparticles

• Rapid Li+ discharge with Li–Mn spinel nanoparticles

• Oxidation catalysis of several organic reactions with various MMO nanoparticles for green chemical production

23

Lithium recovery from (sea)waterH+

Li+

LiMn2O4 spinel λ-MnO2

• Li–Mn spinel oxide is expected as a Li recovery material because of its very high selectivity for Li+.[1]

• Problem is Mn leaching during Li+ extraction.

Redox-type mechanism[1,2]

4(Li)[MnIIIMnIV]O4 + 8H+ → 3()[MnIV2]O4 + 4Li+ + 2Mn2+ + 4H2O

Ion-exchange-type mechanism[2]

(Li)[MnIIIMnIV]O4 + H+ → (H)[MnIIIMnIV]O4 + Li+

[1] Q. Feng et al., Langmuir 1992, 8, 1861.24 [2] K. Sato et al., J. Solid State Chem. 1997, 131, 84.

17

Li+ extraction resultsCrystallite size dependence was examined.

Mn leaching was suppressed The change in the oxidation for smaller Li–Mn spinels. state was suppressed for

smaller Li–Mn spinels.Ion-exchange-type mechanism is dominant for Li–Mn spinel nanoparticles.

25

pH dependencebefore treatment

pH 7

pH 6pH 5pH 4pH 3pH 2pH 1

before treatment

pH 7

pH 6• Nanoparticles show high pH 5

pH 4performance on both Li+pH 3extraction and Mn dissolution.pH 2• Crystal structure of nanoparticles pH 1is stable at various pH.

26

18

Reason for the size effectIon-exchange-type mechanism

(Li)[MnIIIMnIV]O4 + H+ → (H)[MnIIIMnIV]O4 + Li+

Redox-type mechanism4(Li)[MnIIIMnIV]O4 + 8H+ → 3()[MnIV

2]O4 + 4Li+ + 2Mn2+ + 4H2O

In the ion-exchange-type mechanism, both extraction of Li+and insertion of H+ occur at the same time. Therefore, mass-transfer should play a crucial role in this mechanism.

Surface Li extraction by the Ion-exchange-type mechanism proceed probably on the surface only.For nanoparticles, almost entire volume is “surface.”Large particle Nanoparticle

27

Lithium ion secondary battery

• For lithium ion secondary battery, LiMn2O4spinel is a promising cathode material that is low cost, environmentally benign, and with high potential.[1]

• Size reduction of LiMn2O4 is important for the improvement of rate performance.LiMn2O4 spinel

The charge-discharge experiments were performed for Li–Mn spinel nanoparticles supported on graphene nanosheets.

28 [1] J. O. Besenhard et al., Adv. Mater. 1998, 10, 725.

19

Charge–discharge processes of LiMn2O4

Charge Discharge Discharge

–Li +Li +Li

λ-MnO2 LiMn2O4LiMn2O4 Li2Mn2O4

Mn(+3.5) Mn(+4.0) Mn(+3.5) Mn(+3.0)

Irreversible process

• For cathode materials, the discharge process is limited by the Li-insertion reaction.

• Over-discharge causes irreversible degradation.

29

4 V regionReversible intercalation occurs, retaining the spinel structure.

3 V regionIrreversible structural transition occurs from the spinel structure to the rock salt structure. Usually, this region is not used for cycling.

30

20

High-rate performanceCharge-discharge curve at 100C Change in discharge capacity

Theoretical capacity 4 V region: 148 mAh/g

• Discharge capacity was 134 mAh/g even at 100 C rate (=14.8 A/g).• Potential range was lowered to 2 V.• Relatively good cycle retention without phase transitionLi–Mn spinel nanoparticles have good potential for high-rate discharge because of the very short diffusion length.31

Green oxidation catalysisConventional industrial oxidation process

Green oxidation process

Requirements

• Heterogeneous catalysts • Oxidants producing less • Small number of steps byproducts• High selectivity for products • Mild conditions

32 [1] N. Mizuno et al., Coord. Chem. Rev. 2005, 249, 1944.

21

Usefulness of MnOx

Merits of MnOx as catalysts

• Mn cation has various oxidation states.⇒ Good catalyst for oxidation reactions

• MnOx readily adsorb/desorb oxygen atoms on the surface.⇒ O2 can be used as an oxidant.α-MnO2

Mn-based oxides are promising as green oxidation catalyst and catalyst support.[1,2]

[1] S. L. Suib, Acc. Chem. Res. 2008, 41, 479.33 [2] K. Yamaguchi et al., Angew. Chem. Int. Ed. 2013, 52, 5627.

Oxidation ability

React. temp. 0 °C

• Li–Mn spinel nanoparticles with high surface area efficiently catalyzed oxidative homocoupling of thiols.

• The reaction was very fast even at 0 °C.

34

22

Oxygenation of organic compoundsOxygenation of sulfides

150 °C

5 atm O2

Oxygenation of alkylarenes150 °C

5 atm O2

Li–Mn spinel nanoparticles efficiently catalyze oxygen-insertion reactions using O2 as an oxidant.

35

Comparison of various catalysts

*OMS-1: 1D tunnel structure, birnessite & buserite: 2D layered structure

• The samples were synthesized by the novel low-temperature method.

• Li–Mn spinel and Co–Mn spinel have exceptionally high surface areas.

36

O

ac

23

Hydration of nitrile

High activity

Optimized Hydration condition of nitrile

37

Reaction mechanisms1st step: Ammoxidation of alcohol

alcohol aldehyde aldimine nitrile

Catalyzed by surface adsorbed O 1s XPS spectra Latticeoxygen H or surface ads. oxygen[1]

activated oxygen[1]

2nd step: Hydration of nitrileSurface ads. Co–Mntivated H2O[1] spinel

nitrile amideLi–Mn

Catalyzed by surface adsorbed H2O spinel

The surface activation properties depend on the composition.

38 [1] S. L. Suib et al., ChemCatChem 2013, 5, 2306.

24

Conclusions• Mn-based MMO nanoparticles with 1D, 2D, and 3D

nanospace structures were synthesized at low temperature.• Use of molecular Mn precursor is useful to form amorphous

precursor with low crystallization activation energy.• Use of organic solvent and templating cation is effective to

form the spinel structure at low temperature.• The resultant MMOs exhibited unique properties for Li

recovery, Li ion battery, and oxidation catalysis.

AcknowledgementsProf. Noritaka MizunoProf. Kazuya Yamaguchi FIRST Program from MEXTDr. Yumi Miyamoto

LiteraturesY. Miyamoto, Y. Kuroda et al., Sci. Rep. 2015, 5, 15011.Y. Miyamoto, Y. Kuroda et al., ChemNanoMat 2016, 2, 297.39

25

Summer School Japan 2017

Piotr Bujlo, Cordellia Sita and Sivakumar Pasupathi

HySA Systems 1kWe CHP system

Department ofHySA: Hydrogen South AfricaScience & Technology

University of University of North West Cape Town / the Western University /

MINTEK Cape CSIR

Materials and Components Systems and Components and Systems Infrastructure

1 Manganese1 Vanadium2 Zirconium

26

Department ofHySA: Hydrogen South AfricaScience & TechnologyMotivation for the programme

Rank in SA Mineral the World Resource

1 Gold1 Platinum1 Titanium1 Chromium

SA to become a global player & leader in HFC technologies based on SA Natural

Resources

Key Programme 1: Department ofScience & TechnologyCombined Heat and Power

Objectiveto integrate and validate complete CHP systems through innovative

process organization that complement and support the fuel cell stack

and lead to exploitation of the maximum potential of locally

developed components (especially that of catalysts and MEAs),

thereby paving way for internationally competitive and marketable

components and CHP systems

27

High Temperature PEMFC Department ofScience & Technology

AdvantagesOperation at elevated temperature 160-200oC

Resistance to CO concentration in anode feed gas up 3-5%

Membrane conduction mechanism independent on water content

BoP/System symplification

No problems with water management

High quality waste heat

DisadvantagesMembrane, electrode and catalyst degradation

Performance and durability

Key Programme 1: Department ofScience & TechnologyCombined Heat and Power

Development of MEAs and components suitable for HT-PEMFCDevelopment & testing of HT-PEMFC stacks (< 5 kW)Development & testing of HT-PEMFCs based CHP systems

HT MEAs Stacks CHP Systems

Development of MEAs and componenDevelopment & testing of HT-PEMFC sDevelopment & testing of HT-PEMFCs

Development of MEAs and components suitable for HT-PEMFCDevelopment & testing of HT-PEMFC stacks (< 5 kW)Development & testing of HT-PEMFCs based CHP systems

28

Key Programme 1: Department ofScience & TechnologyCombined Heat and Power

ts suitable for HT-PEMFCtacks (< 5 kW)based CHP systems

HT MEAs Stacks CHP Systems

Key Programme 1: Department ofScience & TechnologyCombined Heat and Power

HT MEAs Stacks CHP Systems

Mea

n C

ell V

olta

ge [V

] Total Stack Power [W

]

29

1 kW HT-PEMFC CHP System Department ofScience & TechnologyDesign Assumptions

1 kW CHP System prototypeHT PEM Fuel cell stack 1 kWel

Operating temperature 120-160oC Anode supply: reformate Cathode supply: Air, dry

Steam reformer supplied with methane

Targeted Specification

Electrical / thermal power 1000 Wel / 1500 Wth

Type of fuel Methane, City gas

6 kWhEnergy storage module 6 kVA for 1 hour or 1 kVA for 6 hours (ESM) without methane gas consumption

Thermal storage module 150 litres @ 55-65°C(TSM)

Electrical efficiency up to 40 %Thermal efficiency up to 55 %

Total efficiency up to 85-90 %

PM&ESM 1152x320x2100 mm Dimensions (LxWxH) RFCM 1280x750x1290 mm

TSM 620x1635 mm (ØxH)

HT PEMFC Stack Department ofScience & TechnologyTesting and Validation

49 cell stack; 1 kWel power electrode active area = 96 cm²anode: H2, stoich.=1.25, pabs=1 bar, dry; cathode: Air, stoich.=2.00, pabs=1 bar, dry

0.9 1000Operating parameters: 49 cell stack; 1 kW power; electrode active area = 96 cm²

elanode: pure H2, stoich.=1.25, pabs=1 bar, dry; cathode: Air, stoich.=2.00, pabs=1 bar, dry 800

/ U/P; 160oC0.8/ U/P; 140oC/ U/P; 120oC

600

0.7

400

0.6200

0.5 00 50 100 150 200 250 300 350 400

Current Density [mA/cm2]

30

Fuel processor Department ofScience & Technology

FLOX® Reformer compact C1-HT

ReformingFeed InputNatural Gas, LPG, Methanol (S<1ppm) (10°C<T<40°C, pmax. 0 mbar)Water (DI <1μS/cm, p=6bar) 1,1-1,4l/h

Reformate output approx. 2 Nm³/h (depending on S/C)Hydrogen >75%, 20 slm (1,2 Nm³/h)CO2 < 20%Methane < 2%CO < 1%Temperature 200-250°CPressure approx. 150 mbarEfficiency 80%

1 kW HT-PEMFC CHP System Department ofScience & TechnologyInstallation

FC-CHP System has been successfully installed at HySA Systems Laboratory, hosted by UWC and located at SAIAMC Innovation building

Thermal Energy Storage Module

Power Management & Energy Storage ModuleReformer & Fuel Cell Module

Pow

er [k

W]

Pow

er [k

W]

31

1 kW HT-PEMFC CHP System Department ofScience & TechnologyStart-up

HMI screenshot System temperatures & stack electrical values

1 kW HT-PEMFC CHP System Department ofScience & TechnologyTesting - VDI 4655 Standard

Reference load profiles of single-family and multi-family houses for the use of CHP systems

Daily electrical-energy demand Daily domestic hot water demand

Avarage electrical load profile based on VDI 46552,0 0,4

DHW demand profile based on VDI 46554 persons SFH (single family house) in Berlin4 persons SFH (single family house) in Berlin1,8 SWX - summer working daySWX - summer working dayDemand 15.519 kWh/day1,6 Demand 3.797 kWh/day (about 30dm3/pers/day)

0,31,4

1,2This cor responds to 5 dm3 of water

drained in 1 min , (22 peaks)1,0 0,2

0,8

0,60,1

0,4

0,2

0,0 0,00 5 10 15 20 25 0 300 600 900 1200 1500

Time [h] Time [h]

32

1 kW HT-PEMFC CHP System Department ofScience & TechnologyOperation under VDI 4655

1 kW HT-PEMFC CHP System Department ofScience & TechnologySummary and future works

• 1 kW HT-PEMFC based FC-CHP system has been developed at HySASystems

• System has been successfully installed at HySA Systems laboratory and operated to verify design assumptions and performance specification

• The system will be further operated and validated using reference load profiles of single-family house for the use of CHP systems

• Optimisation of the system construction and operation strategy will be performed to improve operating characteristics and increase system efficiency

33

Department ofScience & Technology

Thank you for listening!Dr Cordellia Sita

HySA Systems Competence CentreSouth African Institute for Advanced Materials Chemistry

University of the Western CapeRobert Sobukwe Road, Private Bag X17

Bellville 7535, South AfricaWebsite: www.hysasystems.com

E-mail: csita@uwc.ac.zaPhone: +27 21 959 9319

Fax: +27 21 959 15 83

34

Abstracts of

Student Poster Session

35

LONG-TERM STORAGE AND DISTRIBUTION OF HYDROGEN WITH IRON-BASED OXYGEN CARRIER MATERIALS

Sebastian BOCK, Robert ZACHARIAS, Viktor HACKER

Graz University of Technology, Institute of Chemical Engineering and Environmental Technology, NAWI Graz, Inffeldgasse 25/C, 8010 Graz, Austria

Keywords: Hydrogen storage, Hydrogen distribution, steam iron process, chemical looping

HYDROGEN STORAGE IN OXYGEN CARRIER MATERIALS At Graz University of Technology the reformer sponge iron cycle (RESC), a fixed bed chemical looping hydrogen process, was proposed for hydrogen production from various bio-based feedstock [1,2]. The evaluated stabilised oxygen carrier material is also suitable for hydrogen long-term storage and distribution in appropriate enclosures with a high energy density for providing decentralised hydrogen allocation. In case of medium- and long-term storage, i.e. for time shifted production and demand, the oxygen carrier is efficiently loaded by large-scale iron reduction. Reducing syngas from both fossil or renewable resources is supplied for instance from wind-powered electrolysis or biogas from waste disposal sites. The oxygen carrier can be stored either at ambient temperature for long-term storage or kept at elevated discharging temperature for medium- and short-term storage. Especially because of the non-toxic and non-pressurized storage constituents the hydrogen storage material can be easily handled and shipped to distributed external consumers as an hydrogen storage media. The oxygen carrier material offers a high volumetric energy density of 90 g l-1 for a ready-to-use pelletised material. Compared to a state-of-the-art tube trailer transportation at 40 bar (4 g l-1), it offers a more than 20-times higher volumetric storage density. This is especially of interest for large-scale and transnational hydrogen distribution, i.e. for shipping or truck and railway transportation in standardised container solutions.

Fig. 1 Infrastructure for hydrogen on- site storage and hydrogen distribution and decentralised on- demand release.

36

For the generation of hydrogen at the disposal site, the storage unit is heated to a certain temperature and pure hydrogen is released from a steam feed. With respect to appropriate construction of the storage solution, also high-pressure hydrogen generation is possible, as presented by our research group in various publications [3-5].

THERMODYNAMIC EVALUATION For a full thermodynamic evaluation, both the storage and the discharging process have to be considered. Fraser et.al. expected a process efficiency of 75% for combined loading and unloading of the oxygen carrier from a hydrocarbon feedstock for the RESC process [6]. Assuming an appropriate loading facility with a suitable energy recovery system from the lean gas, a high degree of feed gas utilisation of 70%, referring to the thermodynamic equilibrium of the Fe3O4 – FeO reduction step, is expected. However, this utilisation ratio also includes the production and as most significant feature the integrated hydrogen purification, referring to the steam-iron process. In addition, no further compression step is required to achieve a high energy density. For medium-term on-site storage, the oxygen carrier is kept at a suitable release temperature and can be discharged on demand. Assuming a suitable system design, no additional heating is required for hydrogen release. The highest energy amount of the discharging process is demanded for long-term storage to heat up the storage material from ambient temperature to operating temperature. This case equates to the decentralised hydrogen generation on site. Assuming the ideal heat capacity of the oxygen carrier material, the required heat quantity is approx. 3-6% of the produced hydrogen LHV. The steam generation requires additional 20% of hydrogen LHV for discharging the hydrogen storage. However, the opportunity of high-pressure hydrogen release would lead to considerable savings in the allocation of pressurized hydrogen for tank systems as demanded for automotive use.

ACKNOWLEDGEMENTS Financial support by the Austrian Federal Ministry of Transport, Innovation and Technology (BMVIT), the Austrian Research Promotion Agency (FFG) through the energy research program.

REFERENCES [1] Gerd Rabenstein, Viktor Hacker. Hydrogen for fuel cells from ethanol by steam-reforming, partial-oxidation and combined auto-thermal reforming: A thermodynamic analysis. J Power Sources 2008; 185: 1293–1304. [2] V. Hacker, “A novel process for stationary hydrogen production: The reformer sponge iron cycle (RESC),” J. Power Sources 2003; 118: 1–2, 311–314. [3] G. Voitic, S. Nestl, M. Lammer, J. Wagner, and V. Hacker, “Pressurized hydrogen production by fixed-bed chemical looping,” Appl. Energy 2014; 157: 399–407. [4] G. Voitic, S. Nestl, K. Malli, J. Wagner, B. Bitschnau, F. A. Mautner, and V. Hacker, “High purity pressurised hydrogen production from syngas by the steam-iron process,” RSC Adv. 2016; 6: 53533. [5] Nestl S, Voitic G, Lammer M, Marius B, Wagner J, Hacker V. The production of pure pressurised hydrogen by the reformer-steam iron process in a fixed bed reactor system. J Power Sources 2015; 280: 57–65. [6] S. D. Fraser, M. Monsberger, and V. Hacker, “A thermodynamic analysis of the reformer sponge iron cycle,” J. Power Sources 2006; 161: 1, 420–431.

37

DETECTION OF CRITICAL CONDITIONS IN POLYMER ELECTROLYTE FUEL CELLS USING IMPEDANCE SPECTROSCOPY AND TOTAL HARMONIC DISTORTION ANALYSIS

Kurt Mayer1, Jan Senn1, Viktor Hacker1

1Institute of Chemical Engineering and Environmental Technologies, Fuel Cell Systems Group, Graz University of Technology, Inffeldgasse 25C, 8010 Graz, kurt.mayer@tugraz.at

Keywords: PEMFC, flooding, dry out, electrochemical impedance spectroscopy (EIS), total harmonic distortion analysis (THDA).

38BINTRODUCTION

Due to the rapid increase in CO2 emissions mankind is confronted with the threat of climate change nowadays. In order to decrease greenhouse gases more renewable energy sources have to be introduced. One of such technologies is the polymer electrolyte fuel cell (PEMFC) which can be established in the mobile sector. There are many advantages of the initiation of PEMFCs. Firstly there are no greenhouse gas emissions secondly the energy conversion efficiency is higher than in gasoline operated cars and it has a high power density. Unfortunately there are also some disadvantages of PEMFCs. Two of the biggest drawbacks are the lifetime and the costs of these fuel cells that prevent them from being commercially available on large scale up to now.

This paper will concentrate on the detection of flooding and dry out in PEMFCs using electrochemical impedance spectroscopy (EIS) and total harmonic distortion analysis (THDA).

EXPERIMENTAL

For all measurements a PEMFC stack was obtained from ZBT (Duisburg). It consisted out of five fuel cells, the active surface area of one cell is 50 cm2. On the anode side hydrogen with a mass flow of 1.2 l h-1 and a stoichiometry of 1.5 was provided, on the cathode side synthetic air with a mass flow of 3 l h-1 and a stoichiometry of 2.5 was set. All experiments were conducted under ambient pressure.

During measurement series the temperature of the stack was kept constant while recording impedance spectra at different operating points. Afterwards the temperature of the humidifiers was changed in 10 °C steps from 50 °C to 80 °C. EIS measurements were performed in galvanostatic mode at an alternating current amplitude of 500 mA within a frequency range between 10 kHz and 100 mHz with the power potentiostat PP240 and the software “THALES” by Zahner Elektrik.

For analysis of obtained impedance spectra a basic equivalent circuit was used which represents nearly all losses in the fuel cell stack. It consists out of a resistor (representing the electrolyte resistance) in series with a series connection of two parallel resistor - constant phase element circuits (representing the charge transfer at the electrode-electrolyte interface and the mass transport effects at the electrode-electrolyte-gas phase interface). For fitting the impedance spectra with the equivalent circuit model, the fitting logarithm of the program “ZView®” by Scribner Associates Inc. was used.

38

While recording impedance spectra the harmonic distortion signals were logged. With this data THD (see Equation 1) analysis was performed.

(1)40B

RESULTS AND DISCUSSION

In Table 1 the fitted data of the EIS measurements are exhibited at the operating point 0.1 A cm-2 at different temperature of the humidifiers. At all times the temperature of the stack was kept at 70 °C. At lower temperature of the humidifiers, which resembles a dry out event, the electrolyte resistance is significantly higher than at optimal conditions. At higher temperature of the humidifiers, which resembles a flooding event, the electrolyte resistance slightly increases again.

Table 1: Electrolyte resistance in dependency of temperature of humidifiers.

The THD data of two different EIS measurements are plotted in Figures 1a (dry out, temperature of humidifier: 50 °C) and 1b (flooding, temperature of humidifier: 70 °C). The stack temperature was at 60 °C. Both figures show that at low frequencies peaks can be identified.

Figure 1: THD spectra of EIS measurement; stack temperature: 60 °C, operating point: 0.3 A cm-2, temperature of humidifiers: (a) 50 °C, (b) 70 °C

ACKNOWLEDGEMENT

This work is funded by the Austrian Ministry of Transport, Innovation and Technology (BMVIT) and the Austrian Research Promotion Agency (FFG).

Temperature of humidifiers [°C] Electrolyte resistance [Ω cm2] Rate of change [%]

50 (dry out) 1,18 15.7

60 (dry out) 1,02 18.6

70 (optimal) 0,81 0

80 (flooding) 0,82 1.2

tem

pe

ratu

re / °

C

39

2

∗+ 2

2

∗

2

2

2

INFLUENCE OF FEED GAS COMPOSITION ON REDUCTION REACTION FOR FIXED BED STEAM - IRON PROCESS

Verena MARTSCHITSCH, Sebastian BOCK, Robert ZACHARIAS, Viktor HACKER

Graz University of Technology, Institute of Chemical Engineering and Environmental Technology, NAWI Graz, Inffeldgasse 25/C, 8010 Graz, Austria

Keywords: Chemical looping hydrogen, steam iron process, hydrogen production, steam reforming

REFORMER SPONGE IRON CYCLE The Reformer Sponge Iron Cycle (RESC) is a new process for stationary hydrogen production. It is based on the steam iron process and includes a reformer unit for generating a syngas from different hydrocarbon feedstock. The fixed bed chemical looping process is designed to convert hydrocarbons to hydrogen with a quality that surpasses the requirements of low temperature PEM fuel cells. [1] Using vaporized water and e.g. natural gas, a synthesis gas is produced in the steam reformer. With this product gas an iron based oxygen carrier is reduced in a first process step. Second, the oxygen carrier is oxidized with steam to form highly pure hydrogen. The iron based oxygen carrier forms three oxidation stages (i) magnetite Fe3O4, (ii) wuestite FeO and (iii) iron Fe.

PROCESS OPTIMISATION To maximize the efficiency of the process, different steam to carbon-ratios (S/C) from a methane feed for the reforming process were investigated. These parameters can be described using the Baur-Glaessner diagram (Fig. 1). It shows the respective equilibrium concentrations with the relative hydrogen and the relative carbon monoxide equilibria between the three iron oxidation stages [2] according to (1,2).

1300

1200

1100

1000

Fe= (1) 2

900 S/C=1.2800 FeO = (2)

S/C=3 +

Fe3O4700

600CO equlibrium

500 H2 equlibrium400

100 80 60 40 20 0Relative CO and H2 contents / % by mole

Fig. 1: Baur-Glaessner diagram with respective CO and H2 contents at different steam to carbon ratios.

40

The reformer experiments were carried out with a Clariant Reformax 300 LDP 19x16mm ten-holed-rings catalyst. The reformer unit has a volume of 4.8 liter and 124mm in diameter.

The equilibrium composition for different S/C are shown in Fig. 1. With a low S/C=1.2, the distance to the equilibrium concentrations is higher. Therefore, the concentration gradient is higher and more synthesis gas is consumed for the reduction of magnetite to wuestite and furthermore into iron metal. With the high S/C=3.0, the input concentration is very close to the wuestite-iron equilibria. The magnetite will be reduced to wuestite but for reduction to pure iron the concentration gradient is low and will therefore limit the reduction reaction.

The dry syngas composition for different GHSV rates for two different S/C is shown in Fig. 2. The percentage of the methane (CH4) is multiplied by ten for a better illustration of the influence of different GHSV rates. The simulations were carried out with Aspen Plus using the Peng Robinson equation of state. For H2, CO and CO2 the simulation results are consistent with the experimental results. With increasing GHSV the methane slip rises due to the limited catalyst performance and therefore limits the reformer methane conversion at high gas throughput.

100%

80%

60%

40%

20%

0%H2 CO CO2 CH4

S/C 3.0 - GHSV 480 S/C 3.0 - GHSV 640 S/C 3.0 - GHSV 960 S/C 3.0 SimulationS/C 1.2 - GHSV 220 S/C 1.2 - GHSV 400 S/C 1.2 - GHSV 480 S/C 1.2 Simulation

Fig. 2: Dry reformer gas composition for different S/C and GHSV (methane multiplied by 10).

ACKNOWLEDGEMENTS Financial support by the Austrian Federal Ministry of Transport, Innovation and Technology (BMVIT), the Austrian Research Promotion Agency (FFG) through the energy research program.

REFERENCES [1] V. Hacker, „A novel process for stationary hydrogen production: the reformer sponge

iron cycle (RESC),“ Journal of Power Sources 118, pp. 311-314, 2003.

[2] S. Fraser, M. Monsberger und V. Hacker, „A thermodynamic analysis of the reformer sponge iron cycle,“ Journal of Power Sources 161, pp. 420-431, 2006.

41

ANODE CATALYSTS FOR THE ALKALINE DEFC TESTED IN A SINGLE CELL USING POLYBENZIMIDAZOLE MEMBRANE

Johanna Ranninger, Bernd Cermenek, Viktor Hacker

Institute of Chemical Engineering and Environmental Technology, Fuel Cell Sytems Group, Graz University of Technology, NAWI Graz, Inffeldgasse 25C, 8010 Graz, Austria. ranninger@student.tugraz.at

Keywords: Ethanol, alkaline DEFC, palladium, polybenzimidazole membrane

8INTRODUCTION

The alkaline direct ethanol fuel cell (DEFC) is a promising opportunity for a completely renewable electricity generation. Unlike hydrogen which mainly originates from the steam reforming process, ethanol is obtained from fermenting sugar containing raw materials. However, the high theoretical efficiency of the DEFC (97%) is drastically reduced due to the incomplete oxidation of ethanol to acetic acid (11%) [1]. The goal of the e!Polycat project is to enhance the performance of the alkaline DEFC by developing sugar based anion exchange membranes (AEM) with high ion conductivity and high mechanical, chemical and thermal stability. Furthermore, stable and ethanol tolerant cathode materials are investigated because ethanol-crossover through the membrane cannot be totally omitted. However, the main focus of this study is to develop highly active and stable anode catalysts which are tolerant toward byproducts of the ethanol oxidation reaction (EOR) in alkaline media.

EXPERIMENTAL

Within the scope of the project, binary and ternary Pd-based catalysts are synthesized using the simultaneous reduction method. Various metal precursor salts are dissolved in aqueous media and mixed with carbon black Vulcan XC72R as carrier. These metal precursor salts are reduced to respective metals on the carrier by adding sodium borohydride (NaBH4) or hydrogen (H2). As additives e.g.: Ni or P are used to improve the activities and stabilities of Pd based catalysts [2,3]. Firstly, the catalysts are characterized in a rotating disk electrode (RDE) experiment via cyclic voltammetry (CV) and chronoamperometry (CA) to get an impression of their activities and stabilities (see Fig. 1, left).

Fig. 1: RDE experimental set-up (left) and the catalyst film on the RDE as working electrode (middle) for the electrochemical characterization, In-house designed single cell (right).

After RDE tests, the performances of the catalysts in form of electrodes are tested in an in-house designed membrane based single cell (see Fig. 1, right) under various operating

42

conditions. An alkalized polybenzimidazole membrane (PBI) is used as electrolyte for the cell measurements. Therefore, electrodes and membrane are prepared as follows:

• The prepared anode catalysts along with 20wt.% of FAA-3 ionomer as binder are merged with n-propanol and sonicated for 30 min. The catalyst suspension is applied dropwise on ELAT-H carbon cloth to result in a loading of 1 mgPd cm-2 [4].

• For the cathode preparation, a commercial perovskite (La0.8Sr0.2)95MnO3-6 is used as catalyst. The active layer (AL) is prepared by weighing in 60wt.% catalyst, 20wt.% Vulcan XC72R and 20wt.% binder (FAA-3 ionomer, PTFE) in n-propanol. The AL is rolled until a leathery texture is obtained. Toray paper is used as gas diffusion layer (GDL). The cathode is dry-pressed and hot-pressed at 110 °C [5,6].

• The PBI membrane is alkalized for 7 days in 6.0 M KOH and rinsed with ultra-pure water before usage.

RESULTS AND DISCUSSION

Polarization curves of the membrane-electrode assembly (MEA) consisting of the in-house Pd/C based anode, the PBI as commercial AEM and the perovskite based cathode, were recorded at three different temperatures.

Fig. 2: Half-cell performance (left) and cell measurements (right) of MEA (Pd/C_PBI AEM_(La0.8Sr0.2)95MnO3-6) at 30 °C, 45 °C and 60 °C in a mixture of 1.0 M KOH and 1.0 M EtOH with a flow rate of 10 ml min-1.

With enhanced temperature, an increase in power density of the single cell measurement with PBI-membrane was observed (see Fig. 2, right). The increase in temperature enhances the kinetics on both electrodes leading to a better performance (see Fig. 2, left).

CONCLUSION

RDE measurement is a powerful method for catalyst screening but the results can vary in the single cell. The MEAs tested in the in-house prepared single cell give reproducable results and allow the comparison of different anode catalysts.

ACKNOWLEDGMENT

Financial support by the Austrian Federal Ministry of Transport, Innovation and Technology (BMVIT), The Austrian Research Promotion Agency (FFG) and the IEA research cooperation is gratefully acknowledged.

REFERENCES

[1] L. An, T.S. Zhao, Y.S. Li, Renew. Sustain. Energy Rev., 2015, 50, 1462–1468. [2] R. Jiang, D.T. Tran, J.P. McClure, D. Chu, ACS Catalysis, 2014, 4, 2577-2586. [3] S.Y. Shen, T.S. Zhao, J.B. Xu, Y.S. Li, Electrochem. Comm., 2010, 195, 1001-1006. [4] C. Grimmer, R. Zacharias, M. Grandi, B. Cermenek, A. Schenk, S. Weinberger, F.A. Mautner, B. Bitschnau, V.

Hacker, J. Phys. Chem. C., 2015, 119, 23839-23844. [5] C. Grimmer, R. Zacharias, M. Grandi, B. Pichler, I. Kaltenboeck, F. Gebetsroither, J. Wagner, B. Cermenek, S.

Weinberger, A. Schenk, V. Hacker, J. Electrochem. Soc., 2016, 163, F278–F283. [6] I. Grimmer, P. Zorn, S. Weinberger, C. Grimmer, B. Pichler, B. Cermenek, F. Gebetsroither, A. Schenk, F.A.

Mautner, B. Bitschnau, Electrochim. Acta, 2017, 228, 325-331.

43

FUNCTIONALIZED CATALYSTS FOR THE OXYGEN REDUCTION REACTION IN HIGH TEMPERATURE PEM FUEL CELLS

Katharina KOCHER1, Clemens Bender1, Viktor HACKER1

1 Graz University of Technology, Institute of Chemical Engineering and Environmental Technology, Inffeldgasse 25/C, 8010 Graz, Austria katharina.kocher@tugraz.at

Keywords: HT-PEM FC, Pt/C@PANI, oxygen reduction reaction, oxidative aniline polymerization

INTRODUCTION

High temperature polymer electrolyte membrane fuel cells (HT-PEM FCs) represent promising candidates for a decentralized energy supply as they can operate directly with reformed hydrocarbons. These energy conversion devices use polymer membranes doped with phosphoric acid (PA, H3PO4), which provide excellent properties for FC application. However, the presence of PA significantly limits the performance of the carbon supported platinum (Pt/C) catalyst toward the oxygen reduction reaction (ORR). This is attributed to the coverage of the Pt surface by several phosphate species, which causes a reduction of the catalyst’s active sites and activity. By functionalizing the Pt/C catalyst with polyaniline (PANI) it is possible to mitigate performance losses due to phosphates adsorption in PA containing environment. PANI forms a protecting thin film around the catalyst particles, thus inhibits the surface coverage of the catalyst by PA and increases its catalytic activity compared to pure Pt nanoparticles. Simultaneously, molecular interactions between the polymer and the catalyst lead to higher stability and durability in HT-PEM FCs employment [1].

EXPERIMENTAL

PANI decorated Pt/C catalysts (Pt/C@PANI) were synthesized through oxidative polymerization of aniline, whereby the starting material was a commercial Pt/C catalyst [1]. The content of PANI was varied in order to investigate the influence of the film thickness on the mitigation of phosphates adsorption. Each catalyst had a metal loading of 50 wt%. The prepared catalysts were ex-situ characterized by means of thin film rotating disk electrode technique using a standard three electrode set-up. In order to determine the active electrochemical surface area (ECSA) and the mass activity (MA), cyclic voltammetry (CV) and ORR measurements were recorded in N2 and O2 purged electrolyte, respectively.

RESULTS

The functionalization of Pt/C with PANI in varying compositions results in Pt/C@PANI catalysts, which are more stable and active in the presence of phosphoric acid compared to a pure Pt/C catalyst. Figure 1 shows the mass activity of the synthesized Pt/C@PANI catalysts (30, 10 wt% PANI) in 0 mM, 1 mM and 5 mM H3PO4 in comparison to the undecorated Pt/C catalyst sample.

44

a) b)

c) d)

Figure 1: a) Mass activities (MA) and b), c), d) ORR curves of Pt/C@PANI catalysts with different PANI contents compared to pure Pt/C in 0.1 M HClO4 electrolyte, in 1 mM and in 5 mM H3PO4.

The Pt/C@PANI30 catalyst consisting of 30 wt% PANI showed the most promising results. In pure electrolyte (0.1 M perchloric acid), a more than twice as high mass activity compared to pure Pt/C was obtained due to molecular interactions. In 1 mM and 5 mM H3PO4 electrolyte the functionalized catalyst showed an increase in mass activity of 27% and 35.5% over the pure Pt/C catalyst, respectively. In the case of 10 wt% PANI no enhancement was achieved as the PANI layer might be too thin to avoid phosphates adsorption. Since the results are encouraging, the employment of Pt/C@PANI catalysts in HT-PEM FC based fuel cell systems should be forced in order to achieve long operating times with high efficiency.

ACKNOWLEDGMENTS

Financial support was provided by The Climate and Energy Fund of the Austrian Federal Government and The Austrian Research Promotion Agency (FFG) through the program Energieforschung (e!Mission) and the IEA research cooperation.

REFERENCES

[1] S. Chen et al., “Nanostructured polyaniline-decorated Pt/C@PANI core-shell catalyst with enhanced durability and activity,” J. Am. Chem. Soc., vol. 134, pp. 13252–13255, 2012

45

EXERGY ANALYSIS OF A POLYMER ELECTROLYTE FUEL CELL (PEFC) Turgay Koroglu1,2, Viktor Hacker3

1Maritime Faculty, Istanbul Technical University, Istanbul, Turkey, tukoroglu@itu.edu.tr, 2Institute of Chemical Engineering and Environmental Technology, Graz University of Technology, Graz, Austria, koeroglu@tugraz.at 3Institute of Chemical Engineering and Environmental Technology, Graz University of Technology, Graz, Austria, viktor.hacker@tugraz.at

Keywords: Polymer electrolyte fuel cell, exergy analysis, energy analysis.

38BINTRODUCTION Polymer Electrolyte Fuel Cells (PEFCs) are fueled with hydrogen which reacts with oxygen of the air via diffusion of the H+ ions towards polymer electrolyte membrane to cathode side to create water, heat and electricity [1]. The reaction is not a combustion process; hence hazardous gases production does not occur because of N2 and other species in the air [2]. PEFCs are gaining importance in power production market due to its compact design, applicability to stationary and mobile systems, decreasing manufacturing costs and increase of efficiency. Yet, the efficiency is not as high as expected. First law of thermodynamics is usually applied to define the situation of the cell however, it lacks of presenting the real thermodynamic performance with respect to the maximum limit [3]. Exergy, which shows not only quantity but also quality of energy, is introduced to overcome this problem. It includes both the first and the second laws of thermodynamics to evaluate investigated states, processes or systems [4]. It is applied to fuel cells [2, 3] and fuel cell systems [5] previously. In most cases, humidification of the streams is neglected in literature. In this study, a laboratory test cell is investigated by applying exergy analysis at different power and voltage couple conditions. It is an experimental purpose fuel cell which of TU Graz [6] with an area of 25 cm2 and a power output of 300mW/cm2 at slightly above atmospheric pressure and 65°C cell temperature conditions. Inlet gases are humidified with relative humidity of 80%. Synthetic air is used with one to four of O2/N2 ratio. Stoichiometry for air and hydrogen is 2 and 1.5 respectively. Power is varied to define the optimal working conditions. Real gas state and ideal gas assumption data are utilized and compared.

38BMETHOD Energy conservation is applied to the cell to determine the heat which is produced by the electrochemical reaction. Moreover, hydrogen, which is fueled to the cell should be considered not only by its physical energy state but also its lower heating value. The cell is stationary, also streams are steady, hence potential and kinetic energies might be neglected. Energy efficiency of a fuel cell is modified and expressed as the power extracted from the cell over hydrogen gas supplied as fuel [1]:

(2a, b)Exergy is the maximum amount of the work that can be obtained while system proceeds from its defined physical and chemical states to the environmental state equilibrium [12]. Its natural behavior is to be destructed with respect to the second law. Therefore, instead of conservation of exergy, it could be balanced as below [4].

46

(3)Determined exergy destruction carries the information about how good is the chemical process of fuel cell. Lastly, exergy efficiency is the true measure of the conversion system:

(4)

38BRESULTS, DISCUSSION AND CONCLUSION Results are derived for the power conditions of 2.50 W, 5.00 W, and 7.35 W are shown in Figure 1 below.

Fig 1. Results of

energy and

exergy analyses

of the PEFC

The produced current rises proportional to the power production, however, the voltage falls due to additional losses in the fuel cell, concurrently. Increase in the power, decreases the energy efficiency due to rise mass flow rates of required inlet streams. Moreover, positive change in the mass flow rate of humidity leads absorbing more heat from released energy of chemical reaction because of the high heat capacity of the water. Exergy rate of the heat is proportional to the heat produced. Exergy destruction is lower than produced electricity power to the limit of 5 W. Beyond that point, exergy destruction piles up more rapidly. The reason of that is, electrochemical reaction occurrence is proportional to the increase in electricity power, and more occurrence of chemical reaction produces more irreversibility related to its natural behavior of entropy generation. Energy and Exergy efficiencies are disproportional to electricity power production because of increasing mass flow rates of inlet streams. Results are slightly different between the assumptions of real and ideal gases. This mainly is caused by the pressure effect for real gases; when the pressure increases, enthalpies of gases tend to follow. However, no difference is observed between efficiencies of both assumptions. Hence, the pressure effect is negligible while it is compared to the lower heating value and the chemical exergy of the streams considered.

REFERENCES 1. Larminie, J., et al., Fuel Cell Systems Explained. 2003, John Wiley & Sons, Ltd,. p.

67-119. 2. Ay, M., A. Midilli, and I. Dincer, Int. J Energ. Res, 2006. 30(5): p. 307-321. 3. Kazim, A., Energ Convers Manage, 2004. 45(11–12): p. 1949-1961. 4. Çengel, Y.A. and M.A. Boles, Thermodynamics: An Engineering Approach. 8th ed.

2014: McGraw-Hill Education. 954. 5. Xiang, J.y., M. Calì, and M. Santarelli, Int. J Energ. Res, 2004. 28(2): p. 101-115. 6. Bodner, M., et al., Membranes, 2015. 5(4): p. 888-902.

47

PERFORMANCE ANALYSIS OF STAND-ALONE HT-PEMFCS BASED TRIGENERATION SYSTEM FOR RESIDENTIAL APPLICATION

Suthida Authayanun1, and Viktor Hacker2

1Department of Chemical Engineering, Faculty of Engineering, Srinakharinwirot University, Nakhon Nayok 26120, Thailand, suthidaa@g.swu.ac.th 2Institute of Chemical Engineering and Environmental Technology, Graz University of Technology, Inffeldgasse 25C, Graz 8010, Austria, viktor.hacker@tugraz.at

Keywords: HT-PEMFC, Trigeneration, Biogas steam reforming, Absorption chiller

The higher quality of heat of HT-PEMFCs compared to LT-PEMFCs makes them applicable for various applications [1]. Heat integration of HT-PEMFCs with an absorption chiller is a promising approach to enhance the overall system efficiency by generating electricity in combination with cooling or refrigeration. In this work, the stand-alone HT-PEMFC based combined cooling, heating and power ( CCHP) system for residential application with the integration of a hydrogen production process and with the target power output of 5 kWel is studied. The biogas steam reformer and the water gas shift reactor are integrated into the system to produce the suitable reformate gas for HT-PEMFCs and the single effect absorption chiller is applied in order to generate chilled water and cooling. The effects of key operating parameters such as temperature, pressure, anode stoichiometric ratio and cathode stoichiometric ratio on energy requirement, energy production, net power consumption, cell performance and efficiency are analysed. The trigeneration system based on stand-alone HT-PEMFCs and adsorption chiller for residential application is shown in Fig. 1. The biogas steam reformer and the water gas shift reactor are used to produce hydrogen-rich gas with low CO concentration (<3% dry basis) for HT-PEMFCs. Biogas is compressed and preheated, mixed with steam and fed into the reformer to produce reformate gas. To avoid CO poisoning of HT-PEMFCs and to enhance hydrogen concentration, the reformate gas is cooled and fed to the water gas shift reactor. The product gas is cooled once more and enters the anode side of HT-PEMFC stack while air is used as an oxidant at the cathode side. The target power output of HT-PEMFC stacks in this work is specified at 5 kWel. The single lithium bromide adsorption chiller is applied to produce chilled water by using heat of the HT-PEMFC stack. The internal air cooling in combination with the external liquid cooling is used to dissipate heat generated in the HT-PEMFCs. The anode exhaust gas and additional bio-gas is used in the afterburner to produce the required heat for the fuel processor whereas the cathode exhaust gas stream is utilized to preheat the inlet air at the cathode. Thermal energy is transported by the heat transfer fluid (Triethylene glycol, boiling point 285 C) from HT-PEMFC to the generator unit of adsorption chiller.

48

Compressor

BiogasReformer WGS reactor

Water

PumpReformate gas

Hot water/Heating space

Compressor Anode off gasAir anodeAfter

DC ACburner HT-PEMFC InverterBiogas

cathodeCompressor

Cathode off gas Flue gas

Excess airCondenser Generator Pump PumpCompressorExpansion Solution Expansion

valve pump valve Thermal storage

Evaporator Absorber

Pump

water Chilled water

Fig. 1 The configuration of a HT-PEMFC-based trigeneration system.

The highest electrical efficiency is achieved at anode stoichiometric ratio below 1.35 and the reduction of the electrical efficiency is observed with an increase in anode stoichiometric ratios from 1.35 to 1.75. Considering the HT-PEMFC operation at low anode stoichiometric ratio, most of the reformate gas from biogas fuel processor is used to generate electricity and the rest is sent to be combusted in the afterburner and thus high electrical efficiency is achieved at this condition. An increase in cathode stoichiometric ratios can enhance the electrical efficiency until it reaches the maximum value at cathode stoichiometric ratio of 4 and then the electrical efficiency decreases with cathode stoichiometric ratios. Due to sluggish of the oxygen reduction reaction at the cathode, the oxygen concentration at the cathode has a crucial effect on the cathode activation loss and also cell voltage. High cathode stoichiometric ratio can improve the oxygen concentration along the cell and thus more electrical efficiency is observed. However, the high power of the air compressor is consumed at high cathode stoichiometric ratios and this results in lowering of the electrical efficiency at cathode stoichiometric ratios above 4. The system efficiency and electrical efficiency enhance when HT-PEMFCs are operated at high temperature because of reduction of voltage loss at high temperature operation. In addition, the maximum electrical efficiency can be reached at cathode stoichiometric ratios of 4-6 while low value of cathode stoichiometric ratio is preferred to achieve high system efficiency. Typically, an increase in operating pressure can enhance the cell voltage by increasing partial pressure of reactant, especially the use of air operation instead of pure oxygen operation at the cathode. However, high net power requirement from the compressors and pumps is observed at high pressure operation and therefore the HT-PEMFCs have to be operated at high current density to reach the target power output.

ACKNOWLEDGMENTS Support from Graz University of Technology, Srinakharinwirot University and the Ernst Mach-Grants-ASEA-UNINET for postdoctoral research at Graz University of Technology is gratefully acknowledged.

REFERENCES [1] Y. Liu, W. Lehnert, H. JanBen, R.C. Samsun, and D.J. Stolten: Power sources Vol.31 (2016), p. 91-102.

49

A research about numerical analysis of gas-liquid two-phase flow in the Gas Channel considering of the GDL

Wang Lida1, Matsumoto Hiroaki2

1Graduate School of Engineering, Yokohama National University,79-1 Tokiwadai, Hodogaya-ku,Yokohama,240-8501,Japan e-mail:wang-lida-yp@ynu.jp 2Graduate School of Engineering, Yokohama National University,79-1 Tokiwadai, Hodogaya-ku,Yokohama,240-8501,Japan e-mail:matsu@ynu.jp

Keywords：PEFC, Gas Channel, CFD, Fluent, Multiphase flow ,Lattice Boltzmann Method

INTRODUCTION： Polymer electrolyte fuel cell (PEFC) have burden on the environment is small, high power density and can operate energy source even at room temperature. Now it has attracted attention as a next generation energy source for mobile or stationary. In previous studies, it analyzed the flow in the Gas channel without considering of GDL (Gas Diffusion Layer),in this study, it shows that how the production water flows in the model that the combination of Gas Channel and a hole picked up from the GDL.

1. Lattice Boltzmann Method as below

A lattice Boltzmann method for two-phase immiscible fluids with large density differences is proposed. The difficulty in the treatment of large density difference is resolved by using the projection method. The method can be applied to simulate two-phase fluid flows with the density ratio up to 1000. 2. Analysis by Fluent Ansys(Fig. 1,Fig. 2)

50

.

Fig. 1

Fig. 2 REFERENCE： 1.M.R. Swift, W.R. Osborn, J.M. Yeomans, Lattice Boltzmann simulation of nonideal fluids, Phys. Rev. Lett. 75 (1995) 830–833. 2. T. Inamuro, T. Ogata, S. Tajima, N. Konishi, A lattice Boltzmann method for incompressible two-phase flows with large density differences, Department of Chemical Engineering, Graduate School of Engineering, Kyoto University, Katsura Campus, Kyoto 615-8510, Japan, Journal of Computational Physics 198 (2004) 628–644 3.Qin Yang, Matsumoto Hiroaki, Research on numerical analysis of gas-liquid two-phase flow of micro-groove.

51

DEVELOPMENT OF CONDUCTIVE OXIDE AS CATALYST SUPPORT OF PRECIOUS -METAL-FREE OXIDE BASED CATHODE FOR PEFCS

Hikaru Igarashi1, Akimitsu Ishihara2, Takaaki Nagai1, Yoshiyuki Kuroda1, Koichi Matsuzawa1, Teko Napporn2,3, Shigenori Mitsushima1,2 and Ken-ichiro Ota1

1 Green Hydrogen Research Center, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama, 240-8501 JAPAN 2 Institute of Advanced Sciences, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, JAPAN 3 University of Poitiers, 4 rue Michel Brunet B27 TSA 5110686073 Poitiers Cedex 09, FRANCE cel@ml.ynu.ac.jp

Keywords:. PEFC, ORR catalyst support, metal oxide

INTRODUCTION In order to widespread for Polymer Electrolyte Fuel cells (PEFCs), development (a)of carbon free electro conductive support for precious-metal-free oxide based cathode catalyst is required, because carbon support is essentially unstable at high potential. We focused on Magneli phase titanium sub-oxide, particularly Ti4O7, because of its high electro-conductivity [1] and electrochemical stability [2]. Magneli phase titanium oxides 50 nmare generally synthesized by reduction heat-treatment at high temperature from titanium (b)dioxide. However, the specific surface area of the reduced titanium oxides becomes quite small due to the severe particle growth by the reduction heat treatment. For the catalyst support, a large surface area is essentially required to highly disperse the catalysts. In this study, we performed hard 50 nmtemplate method to synthesize nano-structured Ti4O7 to reduce contact

Fig.1. SEM image of (a) silica resistance at particle interfaces and prevent template, (b) oxide support after sintering between oxide grains. reduction and removal of template.

EXPERIMENTAL

Titanium nitrate [3] and SBA-15 (silica mesoporous template) were used as the titanium precursor and hard template, respectively. After titanium oxide was deposited in the template pore, reductive heat treatment was performed in 100% H2 atmosphere at 800oC for 5 h. Silica, then, was removed by mixing with 2 M NaOH solution for 2 h and washed

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with distilled water. The morphology of the titanium oxide particle was observed with FE-SEM (SU-8010). X–ray diffraction spectroscopy (XRD, Rigaku Ultima IV) was performed to determine the crystalline structure of the powder. BET surface area was measured by BELSORP-mini II.

RESULT AND DISCUSSION

Fig.1 shows the SEM image of (a) the silica TiO2 template (SBA-15) and (b) the oxide support Ti4O7

after reduction and removal of silica template. rutile Small pores in a regular pattern are observed in the silica template as shown in Fig. 1(a). (A) On the other hand, the rod structure can be observed as negative replica of silica template as shown in Fig. 1(b). The BET surface area of the silica template and obtained oxide support was 925 and 21 m2g-1, (B) respectively. The BET surface area of the oxide that was reduced in same condition without template (precursor: 30nm rutile TiO2) was 5 m2g-1. This difference caused by the use of the template, suggesting that the template can prevent the sintering and 2θ/degree particle growth of titanium oxide existed each Fig. 2. XRDpatterns of (A) oxide template pores. However, the BET value of

support after reduction and removal the obtained oxide support, 21 m2g-1, was of template, (b) oxide sample before much smaller than the theoretical calculated reduction and removal of silica. value, ca. 200 m2g-1, the preparation process

can be further improved.

Fig.2 shows the XRD pattern of (A) the oxide support after reduction and removal of silica template and (B) the oxide sample before reduction and removal of silica template. The peak pattern of the oxide before reduction was identical to rutile type TiO2. (B) The peak pattern of the oxide support after reduction and removal of silica template was identical to Ti4O7.

CONCLUSION

In this study we applied 100% H2 reduction and hard template method to develop nanostructured conductive oxide support with large surface area. We confirmed this method can produce Magneli phase oxide with large surface area and nanostructure. This support can be one of the promising candidates of alternative carbon support.

REFERENCES [1] M. Hamazaki, et al., Electrochemistry, 83, 817 (2015). [2] A. Ishihara, et al., J. Electrochem. Soc., 163, F603 (2016) [3] W. Yue, et al., Chem. Mater., 21, 2540(2009).

AGKNOWREDGEMENT

The authors thank New Energy and Industrial Technology Organization (NEDO) for financial support. This research was supported by Strategic International Research Cooperative Program, Japan Science and Technology Agency (JST). This work was conducted under the auspices of the Ministry of Education, Culture, Sports, Science and Technology (MEXT) Program for Promoting the Reform of National Universities.

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EFFECTS OF ION EXCHANGE CAPACITY ON TOLUENE PERMEABILITY IN PROTON EXCHANGE MEMBRANE

Keisuke Tanimoto1, Kaoru Ikegami1, Kensaku Nagasawa2, Yoshiyuki Kuroda1, Koichi Matsuzawa1, and Shigenori Mitsushima1, 2

1Green Hydrogen Research Center, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan 2Institute of Advanced Sciences, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan E-mail: cel@ml.ynu.ac.jp

Keywords: proton exchange membrane, toluene hydrogenation, ion exchange capacity

INTRODUCTION To introduce the renewable energy for establishment of sustainable society, the large-

scale transportation and storage technologies of energy have been needed to solve the imbalance of energy demand and supply in time and regions. Organic chemical hydride technology, which is an energy career system for hydrogen as the secondary energy, has been attracted attention because it has the advantages of the high volumetric energy density, the easy handling, low toxicity and using petroleum infrastructure. We have focused on the electrohydrogenation of toluene with water decomposition using a proton exchange membrane (PEM) electrolyzer in the toluene-methylcyclohexane organic hydride system [1]. In the electrolyzer, the permeated toluene from cathode to anode through the PEM leads to the degradation of anode [2]. However, kinetics of the toluene permeability for PEMs has not been known well. In this study, we have investigated dependence of temperature and ion exchange capacity (IEC) on toluene permeability for PEMs.

EXPERIMENTAL Nafion®N117 (IEC = 0.909 mmol g-1, d = 183 µm, DuPont), Nafion®NRE212 (IEC = 0.909

mmol g-1, d = 51 µm, DuPont), Aquivion®E87-05S (IEC = 1.15 mmol g-1, d = 53 µm, Solvay) and Aquivion®E98-05S (IEC = 1.02 mmol g-1, d = 54µm, Solvay) were used as the PEMs. Here, IEC is the amount of sulfonic acid groups per weight of polymer. The membranes were immersed in 1.0 M (= mol dm-3) sulfuric acid as pretreatment for overnight. The permeation was evaluated with permeated toluene concentration using a two-chamber cell for 1.0 M sulfuric acid and 100% toluene (Aldrich) which were separated by a PEM. The measurement was conducted at 25, 40, 50, 60 or 70 oC. The permeated toluene concentration in sulfuric acid was determined by the high performance liquid chromatography (HPLC). The sample solution for determination was stabilized with N, N-dimethylformamide (Wako) to be uniform solution with toluene and sulfuric acid in room temperature.

RESULTS AND DISCUSSION The permeated toluene concentration as a function of time, C(t), was represented as the

following equation with linear concentration profile of toluene to thickness direction in a membrane,

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C(t) = Cmax1-exp(SDHt/Vd) (1)

where, S, D, H, t, V, and d are permeation area, diffusion coefficient of toluene, distribution coefficient of toluene at sulfuric acid-PEM interface, time, volume of sulfuric acid, and thickness of PEM, respectively. The Cmax is measured solubility of toluene in sulfuric acid using a separating funnel and the HPLC analysis. The apparent diffusion coefficient of toluene in PEM, which defined as the product of diffusion coefficient and distribution coefficient (= DH) was determined from the C(t) and Cmax using the Fig. 1 Toluene concentration in sulfuric eq. (1). acid with different temperature.

Figure 1 shows the concentration of toluene as a function of time with the various PEMs at 60 oC. The lines were fitted function to the eq. (1). The order of permeated toluene concentration was N117 < E87-05S < NRE212 = E98-05S. C(t) was an exponential of the reciprocal of membrane thickness, so concentration using N117 was much lower than others. Then, the thinner or the lower IEC membrane might have high net toluene permeability.

The Arrhenius plot for apparent diffusion coefficient of toluene in the PEMs is shown in Figure 2. The apparent activation

Fig. 2 Arrhenius plot for apparent diffusion energies for the PEMs were about 23 kJ coefficient of toluene in the PEMs. mol-1, which is typical diffusion coefficient in

aqueous solution with vehicle mechanism. Meanwhile, DH of the Aquivion® PEMs was lower than that of Nafion® PEMs. The DH might be affected by the IEC, because the higher IEC might lead lower toluene solubility by salting-out with higher acidity of hydrophilic region. Consequently, the higher IEC might suppress the toluene permeation in PEM.

ACKOWLEDGEMENTS This work was supported by Cross-ministerial Strategic Innovation Promotion Program

(SIP), “energy carrier” (Funding agency: JST). The Institute of Advanced Sciences (IAS) in YNU is supported by the MEXT program for Promoting Reform of National Universities. We appreciate the person concerned them.

REFERENCE [1] K. Nagasawa, Y. Sawaguchi, A. Kato, Y. Nishiki, and S. Mitsushima,

Electrocatalysis, 8, 164–169 (2017). [2] K. Nagai, K. Nagasawa, and S. Mitsushima, Electrocatalysis, 7, 441–444 (2016).

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ELECTROCONDUCTIVE TITANIUM OXIDE AS SUPPORT MATERIAL OF OXYGEN EVOLUTION ELECTRODE IN ACIDIC ELECTROLYTE

M. Nagai1, Y. Kuroda1, K. Matsuzawa1, A. Ishihara2, S. Mitsushima1, 2

1Green Hydrogen Research Center, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan 2Institute of Advanced Sciences, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan E-mail: cel@ml.ynu.ac.jp

Keywords: Electroconductive titanium oxide, Support, Oxygen evolution

38BINTRODUCTION SPE water electrolysis is important technology as hydrogen production using renewable

energies, however noble metal oxide such as IrO2 is used as an oxygen evolution electrocatalyst, which is a serious problem for cost reduction. In order to reduce precious metal loading, it will be effective to increase the utilization of the electrocatalyst using high surface area support. An electroconductive oxides such as Ti4O7 have been reported as stable support for oxygen electrode of electrolyzers [1]. Oxygen evolution electrode is also important in industrial electrolysis with acidic

electrolyte. In particularly, titanium is used as a substrate material of DSA® (Dimensionally Stable Anode), which is precious metal electrocatalyst coated titanium anode. The DSA® is widely used in industry, but the fundamental characteristic of the interface between catalyst and titanium substrate has not completely clarified such as oxidation state of titanium [3]. As a fundamental study of support of SPE water electrolysis and DSA®, we have

evaluated electrochemical stability of electroconductive titanium oxide film prepared by heat treatment of titanium in low oxygen partial pressure atmosphere.

EXPERIMENTAL A Ti rod (purity: 99.9%, φ: 5.0 mm, h: 4.0 mm) was calcinated in 0.01 %O2 / Ar: 4% H2/ Ar

= 5: 2 at 1050oC for 20 h. For comparison, the Ti rod without treatment and one calcinated in air at 500 oC for 1 h were also evaluated. Their surface oxides were identified by thin film XRD measurement with incidence angle of 2.0o and scanning rate of 2.0o min-1. In order to evaluate their stability, electrochemical measurement was carried out at 30°C

in 0.1 M (= mol dm -3) H2SO4. Cyclic Voltammetry (CV) was performed for 300 cycles in a potential range of from 0.05 to 1.2 V vs. RHE with scan rate of 200 mV s-1. Following to the CV, 10 cycles of Slow scan voltammetry (SSV) with the lower limit potential of 0.6 V vs. RHE with scan rate of 5 mV s-1, and the AC impedance method (EIS) with amplitude of 10 mV, frequency of 10-1- 106 Hz was measured at upper limit potential of the SSV. The upper limit potential increased in the order of 1.6, 1.8, 2.0 V vs. RHE.

RESULTS AND DISCUSSION Figure 1 shows the thin film XRD pattern of the prepared electrodes. Surface of the

electrode calcinated at low oxygen partial pressure was a mixture of Ti4O7 and TiO2. The electrode calcinated in air was Ti colored, which would be interference color of thin titanium

3 Area resistance of the surface oxide film

Fig. 2 Specific excess oxidation change

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oxide film. As a notation, Ti rod calcinated at low oxygen partial pressure, Ti rod calcinated in air and Ti rod without calcination were Ti_Ti4O7, Ti_TiO2, Ti respectively. Figure 2 shows excess oxidation charge as a function of the cycle of the CV to evaluate

stability. The inset figure in Fig. 2 shows the potential and current as a function of time to evaluate oxidation charge passed: Qa and reduction charge passed: Qc. They were calculated by using equation (1), (2). Qa = ∫|I| dt (I ≥ 0) (1) Qc = ∫|I| dt (I < 0) (2)

The vertical axis of the difference between Qa

and Qc divided by the total electric quantity Qa+ Qc should correspond to electric charge passed of irreversible process such as corrosion divided by the sum of the electric charge passed of irreversible processes and the reversible process, which should be almost proportional to electric double layer capacitance, and it would be considered as an index close to the amount of corrosion. For Ti, it became constant at 0.20 after 100 cycles, and it would show continuous corrosion. For Fig. 1 Thin film XRD pattern of the Ti_TiO2 and Ti_Ti4O7, it became constant at prepared electrodes with 2.0 o of the

angle of incidence. 0.05 after 200 cycles and at 0.02 after 50 cycles, respectively. Therefore, the values were reduced to about 1/4 and 1/10 of Ti, respectively. Figure 3 shows the area resistance of the

surface oxide film as a function of the upper limit potential of the SSV. The area resistance of Ti, Ti_TiO2 and Ti_Ti4O7 increased to 4, 14, and 0.8 kΩ cm2 at 2.0 V. Here, the resistance of the Ti_Ti4O7 hardly increased. Therefore, the oxide layer calcinated at low

oxygen partial pressure has low resistance and corrosion protective property.

of (Qa-Qc)/ (Qa+Qc) as a function of ACKNOWLEGMENT cycle number of CV. Inserted figure is current-time characteristic. This work was supported by JSPS KAKENHI

Grant Number JP16K12345. The Institute of Advanced Sciences (IAS) in YNU is supported by the MEXT Program for Promoting Reform of National Universities. We appreciated person concerned.

REFERENCE [1] H. Oh, H. Nong, T. Re ier, M. Gliec h, P. Strasser, Chem. Sci., 6, 3321, (2015). [2] R. Mraz, J. Krysa, J. Appl. Electrochem., 24, 1262 (1994).

Fig. as a function of upper limit potential of SSV.

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MORPHOLOGY-CONTROLLED TITANIUM OXIDE NANO-PARTICLES AS SUPPORTS OF CATHODE CATALYSTS FOR POLYMER ELECTROLYTE FUEL CELLS

YB. Ma1, Y. Ohgi2, T. Nagai1, Y. Kuroda1, K. Matsuzawa1, Y. Liu3, S. Mitsushima1,4, and A. Ishihara4

1 Green Hydrogen Research Center, Yokohama National University, Yokohama, 240-8501, Japan 2 Kumamoto Industrial Research Institute, Kumamoto, 862-0901, Japan 3 College of Chemistry and Molecular Engineering, Peking University, Beijing, 10087, China 4 Institute of Advanced Sciences, Yokohama National University, Yokohama, 240-8501, Japan

*E-mail: ishihara-akimitsu-nh@ynu.ac.jp; +81-(0)45-339-4021

Keywords:. Titanium oxides, Polymer electrolyte fuel cells, Oxide-based supports, Cathode catalysts.

38INTRODUCTION Development of carbon-free electro-conductive supports for oxygen reduction catalysts

is required for widespread of polymer electrolyte fuel cells, because carbon materials are oxidized at high potential. Magnéli phases titanium sub-oxide (TinO2n-1; 4≦n≦10) nano-particles, particularly Ti4O7, were already applied to an alternative material of carbon because of its high chemical stability in acid electrolyte and high electron conductivity [1]. However, although the stability of the Ti4O7 was enough for practical application, the stability of the highly dispersed Pt nano-particles was insufficient. On the other hand, the Pt nano-particles dispersed on nitrogen-doped carbon nanohorn support had superior durability because of their specific morphology. Therefore, the Ti4O7 with nanohorn-like shape is expected to be suitable support to obtain the high surface area for high dispersion and high stability of Pt nano-particles.

High temperature is necessary to reduce TiO2 to Ti4O7 even under reductive atmosphere. We found that the heat treatment at 900oC for 2 h was suitable for reduction of TiO2 nano-particles to Ti4O7 under 100% H2. Such high temperature caused the drastic particle growth due to sintering. Therefore, we tried silica coating of morphology-controlled TiO2 particles to

Fig 1. FE-SEM image of product from restrain the sintering during the reduction 0.3M TiOCl2 heat treatment.

EXPERIMENTAL

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2 M TiOCl2 was used as a precursor[2]. The mixture of 0.3 M TiOCl2 and 1 M HCl was heated at 70oC for 3 h. After heating, the power was washed with a mount of water to remove Cl-. The produced powder was dried at 70oC. The powder was coated with silica using tetraethoxysilane (TEOS) as the silica source according to Ref. [3]. The ratio of TEOS and TiO2 was fixed at 1.9 mL/g- TiO2 in this study. The powders with/without silica coating were heat-

treated under 100% H2 at 900oC for 2 h to Fig 2. FE-SEM image of sample without reduce to Ti4O7. After the reduction heat silica coating after reduction heat treatment. treatment, the powder with silica coating was immersed in 2 M NaOH at 80oC for 24h to remove the coated silica.

REULTS AND DISCUSSION

Fig.1 showed the FE-SEM image of the product from 0.3 M TiOCl2. We successfully obtained morphology-controlled TiO2 with high surface area. Fig.2 showed the FE-SEM image of the sample without silica coating after reduction heat treatment. The sintering of the particles proceeded during the heat Fig 3. FE-SEM image of sample with silica treatment, resulting that the particle size coating after reduction heat treatment and became several hundred nano-meters removal the coated silica. and the morphology was not remained. Fig.3 showed the FE-SEM image of the sample with silica coating after reduction heat treatment and removal the coated silica. Compared with Fig.2, the nanohorn-like shape still remained even after reduction heat treatment, indicating that the silica coating was useful to restrict the sintering at high temperature and to maintain the morphology.

4REFERENCES [1] T. Ioroi, et al., J. Electrochem. Soc., 158, C329-C334 (2011). [2] M. Inada, et al., J. Ceram. Soc. Japan, 117, 819-822 (2009). [3] A. Jaroenworaluck, et al., Surf. Interface Anal., 38, 473-477 (2006)

ACKNOWLEGEMENT

This research was supported by Strategic International Research Cooperative Program, Japan Science and Technology Agency (JST). This work was conducted under the auspices of the Ministry of Education, Culture, Sports, Science and Technology (MEXT) Program for Promoting the Reform of National Universities.

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CATALYTIC ACTIVITY AND DURABILITY FOR OXYGEN EVOLUTION ON La-Ni-O / Ni FOR ALKALINE WATER ELECTROLYSIS UNDER POTENTIAL CYCLING

Yudai Tsukada1, Koichi Matsuzawa2, Yoshiyuki Kuroda3 and Shigenori Mitsushima4 1Green Hydrogen Research Center, Yokohama National University, tukada-yudai-rw@ynu.jp, 2Green Hydrogen Research Center, Yokohama National University, matsuzawa-koichi-zs@ynu.ac.jp, 3Green Hydrogen Research Center, Yokohama National University, kuroda-yoshiyuki-ph@ynu.ac.jp, 4Institute of Advanced Sciences, Yokohama National University, Green Hydrogen Research Center, Yokohama National University, mitsushima-shigenori-hp@ynu.ac.jp,

Keywords:. LaNiO3; alkaline water electrolysis; durability; oxygen evolution reaction

INTRODUCTION Alkaline water electrolysis (AWE) produces hydrogen without any carbon dioxide emission with renewable electric power supply. Anode of AWE is usually used Ni based material which is stable under steady electrolysis. Although fluctuating electricity from renewable energy enhances deterioration of Ni anode, high temperature prepared (Li)NiO/Ni anode has high stability under fluctuated power supply [1]. LaNiO3 is known as high electric conductivity and activity of oxygen evolution reaction (OER) in alkaline electrolyte [2], however durability of LaNiO3 has never investigated under potential cycling. In this study, we have investigated the OER activity and durability of a lanthanum nickel oxide coated on Ni (La-Ni-O/Ni) using various precursors under potential cycling.

EXPERIMENTAL Working electrodes were the La-Ni-O/Nis prepared with thermal decomposition coating of various composition precursors. The precursors were aqueous solutions of La(CH3COO)3 ・ 1.5H2O (Junsei Chemical Co. Ltd., 99.9%), Ni(NO3)2 ・ 6H2O (Junsei Chemical Co. Ltd., 98.0%) with nominal composition of La: Ni = 1.7: 1.0, 1.4: 1.0, 1.2: 1.0 and 1.0: 1.0 in mole fraction to get intermediate composition of La2NiO4, La3Ni2O7, La4Ni3O10 and LaNiO3, and the La-Ni-O/Nis were referred to as La/Ni_1.7, 1.4, 1.2 and 1.0, respectively. The precursor was coated on a Ni plate (The Nilaco corp., 99. +%) with etching to clean up its surface. The process of the coating, drying, and 873 K for 10 min of thermal decomposition were repeated 20 times. Finally, it was baked at 1173 or 873 K for 1 h in air to get a La/Ni_1.7~1.2 or La/Ni_1.0, respectively. Counter and Reference electrode were a Ni coil and a reversible hydrogen electrode (RHE), respectively. All measurements were performed with a three-electrode electrochemical cell at 303±1 K in 7.0 M (= mol dm-3) of KOH. Cyclic voltammetry was applied for 100 cycles between 0 and 1.0 V vs. RHE with the scan rate of 100 mVs-1 as electrochemical pretreatment. The catalytic activity of the OER and the resistance of surface oxide film (Rf) were evaluated by slow scan voltammetry between 0.5 and 1.8 V vs. RHE with the scan rate of 5 mVs-1 and the AC impedance spectroscopy with higher frequency arc at 1.6 V vs. RHE during the duration protocol of potential cycling between 0.5 and 1.8 V vs. RHE with the scan rate of 1 Vs-1. The electrodes were analyzed by XRD and SEM before and after electrochemical measurements.

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RESULTS AND DISCUSSION Figure 1 shows dependence of the Rf as a function of the potential cycle number. The Rfs were much larger than expected from the resistivity La-Ni-Os and thickness of the oxide with the SEM images, therefore the Rfs were affected by formation of NiO, which was confirmed with XRD. The Rf of La/Ni_1.0 was much smaller than others, which were baked at higher temperature than La/Ni_1.0. These values were almost the same during potential cycling. Therefore, the Rfs would be able to reduce by improvement of preparation procedure. Figure 2 shows the iR free polarization curves of the La/Ni_1.7~1.0 and Ni before (a) and after (b) potential cycling. Here, the R is the higher frequency intercept on the real axis, which correspond to the electrolyte resistance. The tails of Ni(II)/Ni(III) redox were observed below 1.45 V vs. RHE, and the Rfs seems to be affect to the difference from the liner region around 1.55 V vs. RHE at higher potential region. The Tafel slope of the La/Ni_1.7~1.0 were almost same around 1.55 V vs. RHE. On the other hand, the current in the Tafel region, which corresponds to the OER activity, of La/Ni_1.0 was much larger than others. According to XRD, the coating of the La/Ni_1.2 and 1.0 was LaNiO3, that of the La/Ni_1.4 was mixture of LaNiO3 and La2NiO4 and that of the La/Ni_1.7 was mixture of LaNiO3, La4Ni3O10 and La2NiO4. OER currents of the La/Ni_1.7~1.0 before potential cycling were almost the same, and they increased during the potential cycling until 4000 cycles at least, although OER currents of Ni dramatically decreased with potential cycling. Therefore, La-Ni-Os are much higher durability than Ni, and LaNiO3 would be the highest OER activity in La-Ni-Os because of the largest current around 1.55 V vs. RHE.

REFERENCES

[1] H. Ichikawa, K. Matsuzawa, Y. Kohno, I. Nagashima, Y. Sunada, Y. Nishiki, A. Manabe, and S. Mitsushima: ECS Trans. Vol. 58(33) (2014), p. 9

[2] R. N. Singh, L. Bahadur, J. P. Pander, and S. P. Singh: J. Appl. Electrochem. Vol. 24 (1994), p. 149

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EFFECT OF CONDUCTIVE SUBSTANCE ADDITION TO NB-DOPED TITANIUM OXIDES AS NON-PLATINUM OXIDE-BASED CATHODES FOR PEFC

T. Tokai1, A. Ishihara2 *, T. Nagai1, Y. Kuroda1, K. Matsuzawa1, S. Mitsushima1,2, and K. Ota1

1 Green Hydrogen Research Center, Yokohama National University, Yokohama, 240-8501, Japan

2 Institutes of Advanced Sciences, Yokohama National University, Yokohama, 240-8501, Japan

*E-mail: ishihara-akimitsu-nh@ynu.ac.jp; +81-(0)45-339-4021

Keywords: PEFC, Non-platinum cathode, Titanium oxides, Conductivity.

INTRODUCTION

Polymer electrolyte fuel cell (PEFC) has already applied to a household stationary power source and a power source for a fuel cell vehicles. However, platinum used as a cathode catalyst for PEFC is less resource and expensive, and its activity and stability as an electrode catalyst are insufficient. Therefore, in order to promote the spread of PEFC, it is necessary to develop a non-platinum catalyst alternative to a platinum, which is inexpensive, abundant in resources, high activity and durability. We have focused on group 4 and 5 transition metal oxides and have developed non-noble metal oxygen reduction catalysts [1]. Furthermore, in order to realize a non-carbon catalyst, we attempted to make a catalyst composed only of oxides. We succesfully demonstrated that non-platinum and non-carbon catalyst was high durable at high potential [2]. Recently, we have investigated the active sites for oxygen reduction reaction (ORR) using Nb-doped titanium oxide thin film as a model catalyst [3]. On the other hand, we cannot evaluate the ORR activity of the powder catalyst properly becuase of its poor conductivity. Powder catalyst is easy to apply to practical use, so it is important to evaluate the ORR activity of the powder catalyst. Therefore, in this study, we have investigated the effect of the addition of conductive substance such as carbon black to Nb-doped TiO2 powder on the ORR activity.

EXPERIMENTAL

Nb-doped titanium oxide powder (Nb-doped amount: 10atm%) was made by high concentration sol-gel method [4] to prepare a precursor. The precursor powder was heat-treated in an electric furnace at 500-1000°C for 10 min in reductive atmosphere, 4%H2/Ar. Ketjen Black (KB) as a conductive substance with a weight ratio of 9 wt% was added to obtained catalyst and the mixture was dispersed in a mixed solvent of 5 wt% Nafion® 6 μL and 1-hexanol 124 μL to make ink. This ink was dropped onto Glassy Carbon (GC) rod to load the 0.10 mg catalyst powder and the rod after drying the solvent was used as a working electrode. We perfomed the electrochemical measurements used a three-electrode type cell in 0.1 mol dm-3 sulfuric acid at 30 ± 0.5 oC. The reference electrode was a reversible hydrogen electrode (RHE), and the counter electrode was a GC plate. Cyclic voltammetry was performed in nitrogen atmosphere with a scan rate of 150 mV s-1 to calculate the electric double layer capacitance. The potential was scanned between 0.2 V

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- 1.2 V vs. RHE in oxygen or nitrogen atmosphere with a scan rate of 5 mV s-1 to obtain the ORR current.

RESULTS AND DISCUSSION

Fig. 1 shows the relationship between the conductivity and the specific surface area of the catalyst with respect to the reduction heat treatment temperature. At 500-700°C, the conductivity is low but the surface area is large, and at 800-1000°C, the conductivity is high but the surface area is small. In particular, from 700°C to 800°C, the conductivity was greatly increased, but the specific surface area decreased to several m2/goxide.

Fig. 1 Relationship between conductivity Fig. 2 compares the influence of addition of KB and specific surface area of catalyst with as a conductive substance on the realtionship respect to reduction heat treatment between the double layer capacitance based on temperature. the mass of the oxide and the reduction heat treatment temperature. The double layer capacitance is considered to be propostional to an electrochemically effective surface area. In case of no addition of KB, the double layer capacitance was almost zero reduction in the heat treatment temperature from 500 to 900oC. On the other hand, in case of addition of KB, the double layer capacitance increased at 600 and 700°C. According to Fig.1, the conductivity of only oxide catalysts prepared at 600 and 700°C was low. However, a current collecting network was formed by adding KB to increase in the electrochemically effective surface area of the

Fig. 2 Relationship between double oxides. layer capacitance and reduction temperature.

REFERENCES [1] A. Ishihara, et al., J. Phys. Chem. C, 117, 18837 (2013). [2] M. Hamazaki, et al., Electrochemistry, 83, 817 (2015). [3] A. Ishihara, et al., Catalysts, 5, 1290 (2015). [4] H. Matsuda, et al., J. Ceram. Soc. Japan, 107, 290 (1999).

ACKNOWLEDGEMENTS The authors thank New Energy and Industrial Technology Organization (NEDO) for

financial support. This work was conducted under the auspices of the Ministry of Education, Culture, Sports, Science and Technology (MEXT) Program for Promoting the Reform of National Universities.

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MODEL ELECTRODE OF OXYGEN REDUCTION CATALYST FOR PEFCS BASED ON TITANIUM OXIDE BY ARC PLASMA DEPOSITION

K. Nagano 1, A. Ishihara2, T. Nagai1, Y. Kuroda1, K. Matsuzawa1, S. Mitsushima1, 2 and K. Ota1

1Green Hydrogen Research Center, Yokohama National University, Yokohama, 240-8501, Japan 2Institute of Advanced Sciences, Yokohama National University, Yokohama, 240-8501, Japan

Keywords: Polymer electrolyte fuel cells, Oxygen reduction reaction, Oxide-based cathode, Titanium oxide 3

Because Polymer Electrolyte Fuel Cells (PEFCs) have high theoretical energy conversion efficiency, practical use as power sources for stationary residential cogeneration system and fuel cell vehicles has already been started. In the present PEFC, platinum nano-particles on carbon support are used as an oxygen reduction catalyst. However, platinum is expensive and has a small resource, and the durability of carbon support is insufficient at high potential. In order to widely commercialize PEFCs, the development of an alternative material as non-platinum cathode is inevitable. In this study, we focused on titanium oxide for alternative material. Because TiO2-based powder catalysts with some ORR activity show a large resistivity, it is difficult to form a sufficient electron conduction path without the existence of the other electro-conductive materials such as carbon. Therefore, it is necessary to evaluate the size and/or the thickness of the titanium oxide-based catalysts whose surface could act as active sites although the catalysts have poor conductivity.

We prepared model catalysts using an arc plasma deposition method. Metal Ti rod was used as target, and oxygen pressure in chamber was controlled to form TiO2 with oxygen vacancies. By changing the number of shots of arc plasma, we could control the average film thickness of titanium oxide on GC rod (φ=5 [mm]) and investigate the effect on the oxygen reduction reaction (ORR) activity. We used three-electrode type cell for electrochemical measurements. The electrolyte was at 0.1 [mol dm-3] sulfuric acid and the temperature was kept at 30 ± 0.5 oC. The reference electrode was a reversible hydrogen electrode (RHE), and the counter electrode was a GC plate. Cyclic voltammetry was performed in nitrogen atmosphere with Fig. 1. Relationship between average film a scan rate of 150 [mV s-1]. The potential thickness and oxygen reduction current was scanned between 0.2 V - 1.2 V vs. density. (0.1 M H2SO4, 30oC)

64

RHE in oxygen or nitrogen atmosphere with a scan rate of 5 [mV s-1] to obtain the ORR current. The ORR activity was evaluated by the oxygen reduction current density based on geometric area (iORR).

Fig. 1 shows the relationship between the average film thickness of TiOx and the iORR at 0.4 and 0.6 V. The iORR increased with increasing the average film thickness of 2 [nm], and drastically decreased. It is well known that the quantum tunneling of electrons through the insulator film occur when the thickness of the insulator is below 2-3 [nm]. Fig. 1 suggested that the surface of the titanium oxide nanoparticles and/or film acted as electrochemical active surface.

Fig. 2. Dependence of electric double layer Fig. 2 shows the dependence of the electric double layer capacitance capacitance of TiO2-based catalysts prepared (C) obtained from the cyclic by APD on average film thickness. voltammograms on the average film thickness. C was almost constant until the average film thickness of ca. 2 [nm], and decreased with increasing the film thickness. The constant of the C below the 2 [nm] indicated that the surface of the titanium oxide in the region electrochemically functioned. When the thickness of the titanium oxide increased above 2 [nm], it was difficult to occur the quantum tunneling of electrons because the titanium oxide films were almost insulator. Therefore, we found that when the particle size or the thickness of the titanium oxide could be prepared to be 2 [nm] or less, all of its surface would act as the active surface even in the powder catalyst. This finding gives the important information in the catalyst design of oxide catalysts with poor conductivity.

Acknowledgements The authors thank New Energy and Industrial Technology Organization (NEDO) for financial support. This work was conducted under the auspices of the Ministry of Education, Culture, Sports, Science and Technology (MEXT) Program for Promoting the Reform of National Universities.

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A VISUALIZATION TECHNIQUE DEVELOPMENT FOR UNSTEADY HYDROGEN CONCENTRATION DISTRIBUTION IN POROUS MATERIALS

Konosuke WATANABE1, Koshi HAMADA2 and Takuto ARAKI3

1Graduate School of Engineering, Yokohama National University, Japan, watanabe-konosuke-td@ynu.jp, 2Graduate School of Engineering, Yokohama National University, Japan, hamada-koshi-zm@ynu.jp, 3Faculty of Engineering, Yokohama National University, Japan, taraki@ynu.ac.jp

Keywords: porous media, unsteady hydrogen concentration, visualization technique

INTRODUCTION Grasping the transport phenomenon of hydrogen in porous materials is a key factor for

developments of hydrogen utilizing equipment. For understanding their start-up and corrosion characteristics [1], measuring unsteady hydrogen concentration distribution on the order of 10-2 sec is required, however conventional measuring methods, such as mass spectrometer, are not sufficient for their time resolution. In this study, a visualization technique using the alloy thin film’s characteristic which reflection rate is changed along with hydrogen concentration [2]. Unsteady hydrogen concentration was measured by this technique, and this result showed the possibility of this technical utility.

EXPERIMENTAL MODEL AND CONDITIONS To measure unsteady hydrogen concentration distribution, we made up a visualization

cell with a hydrogen visualization sheet. Fig. 1 shows a schematic drawing of the visualization cell. A channel exists under the centerline of the GDL. Fig. 2 shows the constitution of a hydrogen visualization sheet, and the reaction formula (1) and (2) shows the mechanism of reflection rate change [3]. Experimental conditions are given in Table 1. Recording the reflection rate change while supplying hydrogen, we take a video of 60fps.

Fig. 1 A schematic drawing of a Fig. 2 Constitution of a hydrogen visualization cell visualization sheet

66

Mg2Ni(silver) + 2H → Mg 2NiH4(brown & transparent) (1) 2

Mg(silver) + H2 → MgH2(transparent) (2)

Table 1 Experimental conditions TGP-H-060 (TORAY) Characteristic of GDL without PTFE and MPL

GDL thickness [μm] 190 Channel depth [mm] 3.0 Channel width [mm] 3.0 H2 flow rate [mL/min] 45

H2

a : 0 sec b : 0.1 sec

c : 0.5 sec d : 1.1 sec

: Channel 0% 100%

Fig. 3 Hydrogen concentration distribution change

RESULT AND DISCUSSION Figure 3 shows the hydrogen concentration distribution change. As time passed, the

concentration in the channel part increased from the inlet side at first, secondly the concentration in the rib part gradually increased. Assuming a plug flow, the time it takes for hydrogen to reach from the inlet to the outlet is estimated to be 1.08 sec. Comparing this time with the result of Fig. 3, they are almost matched. We confirmed that the visualization technique for unsteady hydrogen concentration distribution in porous materials with a hydrogen visualization sheet has been established.

REFERENCES [1] H. Kanesaka: Hydrogen Energy System, Vol. 34, No. 2 (2009), p. 30 [2] Information on http://www.atsumitec.co.jp/products/hydrogen [3] Information on http://www.f-suiso.jp/bunkakai/H23bunkakai/2nd/2nd/H23_2_1.pdf

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MEASUREMENT OF TEMPERATURE DISTRIBUTIONS OF A MICRO-TUBULAR SOEC DURING H2O/CO2 CO-ELECTROLYSIS

Kohei Shimosawa1, Atsushi Maeda2, Toshiki Kawamura3, and Takuto Araki4

1Graduate School of Engineering, Yokohama National University, Japan, shimosawa-kohei-bv@ynu.jp 2Graduate School of Engineering, Yokohama National University, Japan, maeda-atsushi-yk@ynu.jp 3Graduate School of Engineering, Yokohama National University, Japan, kawamura-tosiki-sx@ynu.jp 4Faculty of Engineering, Yokohama National University, Japan, taraki@ynu.jp

Keywords: Solid oxide electrolysis cell, Co-electrolysis, Temperature distribution

INTRODUCTION In recent years, energy from natural energy sources such as solar and wind power has been added to the electric grid, as it is clean and renewable. However, both wind and solar power exhibit instability with respect to changes in the weather. As the proportion of these types of energies increases steadily, adequate controls will become necessary to stabilize the grid. Hydrogen generation systems that employ electrolysis techniques are expected to be used as large-capacity power storage facilities with the ability to stabilize the electrical power supply. In particular, high-temperature steam electrolysis and co-electrolysis using solid oxide electrolysis cells (SOECs) can generate source gases with high efficiency because the heat from the overpotentials can be recycled in the form of a heat source for the electrolysis reaction [1]. In addition, owing to the endothermic nature of the reaction, increases in the temperature of the SOEC will be prevented. Moreover, co-electrolysis, which is simultaneously electrolyzing CO2 and H2O in SOEC can produce H2 and CO at the same time. It is reported that system efficiency of this technology will be higher than it of steam electrolysis due to the fast overall electrochemical kinetics [2]. Furthermore, tubular type SOECs are easy to seal, so they are suitable for electrolysis. However, there are many problems that need to be solved to improve the reliability, durability and electrochemical performance. In particular, understanding of temperature distributions is very important in order to design structure. Therefore, in order to understand complicated phenomena in the cell, both experimental and numerical analysis are effective. Hence, in this study, the temperature distributions were measured by a thermal imaging camera and K-type thermocouples during co-electrolysis. In addition, we measured outlet gas composition and evaluated theoretical value in order to elucidate co-electrolysis reaction process in micro-tubular SOEC.

EXPERIMENTAL APPARATUS For micro-tubular SOEC uses porous Ni-YSZ (the mixture of nickel and YSZ (yttrium stabilized zirconium) as cathode, and dense YSZ as electrolyte, porous LSM-YSZ (the mixture of LSM (lanthanum strontium manganite) and YSZ) as anode. Figure 1 shows a composition of thermocouples, current collectors and sealants. H2 at 5 ml/min, H2O at 10 ml/min, CO2 at 35 ml/min, and Ar at 20 ml/min was supplied as inlet gas. As a method of measuring the temperature, we measured temperatures at three points (upstream, midstream, and downstream) with thermocouples and the entire cell temperature by thermal imaging camera. Operating temperature is 1123K.

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Figure 1. Components for electric and temperature measurements.

RESULT AND DISCASSIONS Figure 2 shows a measured i-V curve. The figure shows that current density increased with voltage increase. The maximum current density was 0.52 A/cm2 at 1.4 V. Figure 3 shows the temperature change from OCV at 1.4 V measured by the thermal imaging camera and the thermocouples at three points during co-electrolysis. The temperature changes measured by the thermal imaging camera were consistent with that measured by thermocouples illustrated in Figure 2. The temperature change is lower than 0 K in the range of z = 0 to 10 mm, increases between z = 10 to 45 mm, and decreases in the range of z = 45 to 50 mm. From this result, the temperature change was found to be caused by endothermic reaction at entrance active area and by exothermic reaction at exit active area. Also, that in the range of z = 40 to 45 mm was found to be caused by electric resistance heat of Pt wire and combustion due to leakage of hydrogen.

Figure 2. Measured i-V curve Figure 3. Temperature change at 1.4 V.

REFERENCES [1] M.A. Laguna-Bercero，Recent advances in high temperature electrolysis using solid oxide fuel cells:A review，Journal of Power Sources，Vol. 203，pp. 4–16，2012. [2]Y. Wang, T. Liu, L. Lei, F. Chen, Fuel Processing Technology, 161(15), 248-228 (2017).

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CONJUGATE ANALYSIS OF HEAT-SPECIES-CHARGE TRANSPORT AND CATALYST OXIDATION IN PEMFC

Satoshi NISHIMURA1, Shoki INOUE2, and Takuto ARAKI3

1Graduate School of Engineering, Yokohama National University, Japan, nishimura-satoshi-vw@ynu.jp 2College of Engineering Science, Yokohama National University, Japan, Inoue-shoki-js@ynu.jp 3Faculty of Engineering, Yokohama National University, Japan, taraki@ynu.ac.jp

Keywords: PEMFC, Catalyst Layer, Oxygen Reduction Reaction, Catalytic Activity

INTRODUCTION Fuel cells can convert chemical energy of hydrogen into electricity directly. They have been expected as power generation systems for automobiles or household power supplies because they have high efficiency and low environmental impact. In particular, polymer electrolyte fuel cells (PEMFCs) can be operated at lower temperature than other types of fuel cells and they can start quickly. However, PEMFCs have many issues such as achieving higher efficiency, reducing their costs. In specific, management of water in the cell is much important to improve its performance. For example, drying of the membrane results in in not only depression of the cell performance but also the degradation of the membrane. On the other hands, excess liquid water in the cell causes inhibition of gas transport [1]. Nevertheless, the water transport mechanism in the cell is complicated and difficult to understand by only experimental methods because the components of the cell are thin and there is interaction among electrochemical reaction, gas transport, heat transport, and phase change of water. Thus, conjugate analysis incorporating all of the phenomena is required. In previous studies, various numerical analyses are proposed and yet few papers have discussed the unsteady cell performance considering two phase flow, non-isothermal condition, and distributions. In addition, few works have incorporated the catalyst oxidation at a high electric potential which inhibits the oxygen reduction reaction (ORR) in the catalyst layer (CL).

ANALYTICAL MODEL To investigate the effect of catalyst oxidation on the cell performance, we used a model based on the agglomerate model developed by Araki et al. [2]. A model of the effect of platinum catalyst oxidation developed by Sugawara et al. was used [3]. We compared conditions with and without catalyst oxidation. Fig. 1 shows the schematic of our model. Table 1 shows the analytical conditions in this study. Fig. 1 Schematic of the analytical model

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RESULT AND DISCUSSION Table 1. Analytical conditions

Fig. 2 and Fig. 3 show current density distributions with and without catalyst oxidation. Current density was lower at the condition with oxidation because platinum oxide inhibited the ORR. The difference between two results appeared under the channel, so that catalyst oxidation seems to have occurred mainly there. Fig. 4 and Fig. 5 show oxygen concentration distributions at two conditions. Oxygen concentration was higher at the condition with catalyst oxidation. It was attributed to lower reaction rate. In other words, more oxygen was left in the CL and its diffusion was less inhibited by liquid water produced by the ORR.

Fig. 2 Current density distribution Fig.3 Current density distribution

(without oxidation) (with oxidation)

Fig.4 Oxygen concentration distribution Fig.5 Oxygen concentration distribution (with oxidation) (without oxidation)

REFERENCES [1] Y. Wang, K. S. Chen, J. Mishler, S. C. Cho and X. C. Adroher, A review of polymer

electrolyte fuel cells: Technology, applications, and needs on fundamental research, Applied Energy, 88(4), pp.981-1007 (2011)

[2] Y. Minegishi, K. Miyagawa and T. Araki, 51st Thermal Engineering Conference 2013

[3] S. Sugawara, Y. Suzuki, S. S. Kocha, and K. Shinohara, Electrocatalytic Activity Analysis of PEFC Cathode by 1-D Macrohomogeneous Model of Catalyst Layer, Electrochemistry, 79(5), pp.404-413 (2011)

Separator Temperature [K] Tcell 343 Gas Pressure [atm] Ptotal 1.0 Gas Humidity [%] RH 100

Channel Width [mm] lch 1.0 Rib Width [mm] lrib 1.0

Overpotential [V] η 0.6

0.4mm

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0 µm

IN-SITU MEASUREMENTS OF HUMIDITY IN A PEMFC CHANNEL USING MEMS SENSORS

Noriyoshi HASEGAWA1,Ryotaro MINAMI2,Yota OTSUKI3 , and Takuto ARAKI4

1 Graduate School of Engineering, Yokohama National University, Japan, hasegawa-noriyoshi-yp@ynu.jp, 2 Graduate School of Engineering, Yokohama National University, Japan, minami-ryotaro-hm@ynu.jp, 3 Graduate School of Engineering, Yokohama National University, Japan, otsuki-yota-xj@ynu.jp, 4 Faculty of Engineering, Yokohama National University, Japan, taraki@ynu.ac.jp

Keywords: PEMFC, cathode channel, humidity distribution, humidity sensor

INTRODUCTION

The proton exchange membrane fuel cell (PEMFC) is a clean and high efficiency power generation system. It has been attracted attention as a hopeful technology, however, there are still several issues to be solved commonly used. One of the most serious issues is water management inside the cell. At high current density operation, liquid water accumulated in a channel, a catalyst layer (CL) and a gas diffusion layer (GDL) lead to PEMFC performance degradation because too much liquid water disturbs the reactant gas to the reaction site. In addition, the inside of PEMFC is complex system because of two-phase flow of liquid water and vapor. So, we need to focus on the vapor transport as well as liquid water to reveal water transport inside the cell. There are some approaches to comprehend the RH inside PEMFCs [1,2]. However, the methods of these reports could not quantitatively measure RH at a channel. So, we have developed thin film humidity sensor (TFHS) using micro-electro-mechanical-systems (MEMS) technology for measuring RH quantitatively at the cathode channel.

THE TFHS BASED ON MEMS TECHNOLOGIES Capacitive type TFHS was developed with MEMS technology. Fig. 1 shows a

schematic view of the TFHS. The sensors consisted of the Parylene® (SCS), Ni and Au. Parylene was selected as not only an electrical insulating material but also a sensing material to obtain a uniform and homogeneous film. The thinner sensing layer is suitable for sensitivity, then sensing layer thickness was set to 0.5 µm. Au and Ni were deposited as reinforcement and electrode. The thickness of Au and Ni was 200 nm and 20 nm, respectively. These were thin enough to obtain water vapor permeability.

Over view 60mm

0.35mm10

Cross section4.0 µm Parylene

200 nm Au0.5 µm Parylene

20 nm Ni 4.0 µm Parylene

9.0 µm

Electrode Au Insulating layer Parylene

Reinforcement Ni Sensing layer Parylene

Fig. 1 A schematic view of the TFHS

72

sensor

RESULT AND DISCUSSION Fig. 2 shows ex-situ calibration results of the TFHSs. We observed capacitance

with an LCR meter (HIOKI, 3590 LCR HiTESTER) changing RH of the air from 30% to 90%. These trends were agreed with L. S. Kuo et al. [3]. Fig. 3 shows inserted position of the sensors at a channel. Sensors were inserted a upstream and a downstream of the channel. Experimental conditions are given in Table 1. Fig. 4 shows the relative humidity change at a upstream obtained by the in situ measurement. It can be seen that the RH in a upstream was saturated at a low current density as the RH of the supply gas was higher. As the RH of the supply gas was high, the PEM was wetted and the local current density distribution becomes uniform. As a result, much moisture was generated upstream.

Fig. 2 Calibration results of the TFHSs Fig. 3 Inserted position of the TFHS at a channel

Table. 1 Experimental condition

Fig. 4 RH change from OCV

REFERENCES [1] C. Y. Lee, W. J. Hsieh and G. W. Wu: J. Power Sources, Vol. 181 (2008), pp. 237-

243[2] K. Nishida, .M. Ishida, S. Tsushima and S. Hirai: J. Power Sources, Vol. 199

(2012), pp. 155-160[3] L. S. Kuo, H. H. Huang, C. H. Yang and P. H. Chen: Sensors, Vol. 11 (2011),

p. 8674

Flow design Parallel-flow Active area [cm2] 10

Channel design Single surpentain

Channel depth [mm] 1.0 Channel width [mm] 1.0

Rib width [mm] 1.0 Gas relative humidity

[%RH] 30, 60

Gas flow rate [Nml/min]

Anode (H2)

100

Cathode (O2)

100

× ×

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ANALYSIS OF VISUALIZATION ABOUT EFFECT OF GDL CONFIGURATION ON WATER DISTRIBUTION INSIDE PEFC

Yusuke TAMADA1, Sota HASHIMURA2, Kaito SHIGEMASA3, and Takuto ARAKI4

1Graduate School of Engineering, Yokohama National University, Japan, tamada-yusuke-nt@ynu.jp

2Graduate School of Engineering, Yokohama National University, Japan, hashimura-souta-bv@ynu.jp

3Department of Mechanical Engineering and Materials Science, Yokohama National University, Japan, shigemasa-kaito-mp@ynu.jp

4Faculty of Engineering, Yokohama National University, Japan, taraki@ynu.jp

Keywords:.PEFC, Water distribution, X-ray CT, GDL, MPL.

INTRODUCTION The polymer electrolyte fuel cell (PEFC) is attracted attention as a clean and high

efficiency power generation system, however it is still facing several problems. One of the crucial problems is water management inside the PEFC. In the gas diffusion layer (GDL), gas transport is interfered by excess liquid water. Hence, proper water management in the PEFC is important for achieving high and stable performance. In addition, generally, GDL is coated with micro porous layer (MPL). The MPL composed of carbon black and hydrophobic material. The MPL is well known to affect water distribution. In this paper, X-ray CT was employed to visualize the liquid water distribution inside PEFC. Four type conditions were prepared for visualizing water distribution. The difference of the condition was porosity and with/without the MPL.

EXPERIMENTAL X-ray CT was used for visualization image of liquid water distribution inside the

PEFC. During the visualization, the tube voltage and the tube current was set at 30 kV and 200 μA, respectively. The number of shots per sample 1 revolution 1800 times, the exposure time was 0.1 s, total visualization time was about 30 minutes. Voxel size of visuarization image obtained by X-ray CT was 2.7 µm. The visualization cell is made of carbon resin, and the active area is 1 cm2. Flow path shape was a parallel flow. The rib width, the channel width, and the channel depth were 1 mm. The cell is fixed to the acrylic cylinder, and it was applied a load of 1 MPa by using springs. Separator temperature of both electrodes was 40 °C. In addition, hydrogen and air were supplied at 1000 ml/min rate in anode and cathode, respectively. And their relative humidity was 80%. In our study, we used four types of GDL. Tabel 1 shows the experimental conditions. Table 2 shows physical properties of GDLs used in experiment.

Table. 1 Experimental condition Table. 2 Physical properties of GDLs

with MPL without MPL

TGP Condition 1 Condition 2 SGL Condition 3 Condition 4

Condition Unit TGP SGL H-060 29BA 29BC

MPL - Thickness µm 190 - 190 235 Porosity % 78 - 88 40-41

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RESULT AND DISCUSSION Fig. 1 shows the images of through-plane water distribution in each conditions. In

these visualization images, degree of saturation is expressed as a brightness value. Location of liquid water remain in existence was described more warm color. These images indicated that liquid water was accumulated under the rib area rather than channel area in all condition. However, in condition 2, most highly saturation area was CL/GDL interface. This result indicated that MPL discharged water in CL/GDL interface. Fig. 2 shows the one dimensional brightness value distribution in cathode GDL rib area. In condition 2, the brightness value at CL/GDL interface was increased, but it couldn’t observed in condition 4. The reason why we got this result is considered to be effect of porosity. In condition 4, liquid water was transported rib and channel side. Fig. 3 shows the i-V curves in each of conditions. Comparing the condition 1 and 2 that is used GDL of TGP, condition 2 rather than lower cell voltage condition 1 that using with MPL. By the same way, in case of SGL indicate lower cell voltage rather than using GDL that is coated MPL. This result suggested that MPL contribute to improve performance of PEFC.

Fig. 1 Images of through-plane water distribution

Fig. 2 Brightness value distribution in cathode GDL rib area Fig. 3 i-V curves each of condition

REFERENCES [1] J. Lee, J. Hinebaugh and A. Bazylak: J. Power Sources, Vol. 227 (2013), pp. 123-130 [2] Paul R. Shearing et al: Electrochimica Acta, Vol. 211 (2016), pp. 478-487

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EXTENSION OF SPECIFIC SURFACE AREA OF IrO2-Ta2O5/Ti ANODE CATALYST

Kohei Maniwa1, Kenji Matsumae1, Kensaku Nagasawa1, 2, Koichi Matsuzawa1, Yoshiyuki Kuroda1, Shigenori Mitsushima1, 2 1Green Hydrogen Research Center, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan 2Institute of Advanced Sciences, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan 79-5, Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan cel@ml.ynu.ac.jp

Keywords: DSA, thermal decomposition, IrO2, Oxygen evolution reaction

INTRODUCTION The DSA®-type electrode, which is precious metal-based catalyst coated titanium, has

been used as an industrial electrolytic oxygen evolution anode with iridium oxide-based coating [1, 2]. This DSA®-type electrode has high oxygen evolution reaction (OER) activity and durability. However, the oxygen evolution overpotential significantly causes the voltage loss in the electrolyzers [1, 3]. The extension of specific surface area in catalyst layer is one of the improvement ways of the performance. However, the reports to increase surface area by eluting material in catalyst layer are few as far as we know [4, 5]. In this study, we have investigated the effect of the addition of silica and the etching it in alkali solution on to electrode property.

EXPERIMENTAL IrO2-Ta2O5-SiO2 (Ir: Ta: Si = 47.5: 47.5: 5 or 50: 50: 0 wt%) catalyst was coated on a Ti

substrate as a working electrode. It was fabricated using the precursor solution of H2IrCl6 ・ nH2O, Ta(OC4H9)5, Si(OC2H5)4 and n-butanol. Calcination condition was following; i. Thermal treatment for 10 min at 520oC in the air, ii. Dipping in the precursor solution, iii. Drying for 10 min at 100oC in the air, iv. Thermal decomposition for 10 min at 500oC in the air and v. Calcination for 1 h at 500oC in the air. From ii to iv was repeated for 20 cycles. The prepared IrO2-Ta2O5-SiO2/Ti electrode was etched in 0.25 to1.0 M (= mol dm-3) NaOH solution or Ta saturated 1.0 M NaOH solution at 60oC. The polarization property and the electrochemical impedance spectroscopy were determined by 3-electrode electrochemical cell with 1 M H2SO4, and the catalyst loading amount was measured by X-ray fluorescence thickness meter.

RESULTS AND DISCUSSION Figure 1 shows the standardized double layer capacitance and surface film resistance

after etched in 0.25 to 1.0 M NaOH solution or 1.0 M NaOH solution with saturated tantalum (ST) for 5 h and 45 h. Double layer capacitance is proportional to the specific surface area [6]. Therefore, higher NaOH concentration and longer etched time led the higher double layer capacitance and lower surface film resistance. Figure 2 shows the Tafel slope before and after etched by 1.0 M NaOH solution for 0 and

45 h. The etching by the high NaOH concentration indicated the improvement of OER activity. Before etching, the OER activity of 5 wt% SiO2 anode was lower than that of 0 wt.%.

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On the other hand, after etching, that of the 5 wt.%-SiO2 anode was same for the 0 wt.%-SiO2 anode. The double layer capacitance of the 5 wt.%-SiO2 anode after etching showed as 1.6 times value as before etching, however, the 0 wt.% SiO2 anode after etching was as same as before etching. For the 0 wt.%-SiO2, decreases of polarization by 45 h etching which was estimated by the surface film resistance were 2.7×10-3 and 0.11 V at 0.01 and 0.4 A cm-2, respectively. Those of 5 wt.%-SiO2 were 4.4×10-3 and 0.17 V at 0.01 and 0.4 A cm-2, respectively. The decreases of polarization by 45 h etching

Fig. 1 Standardized double layer which was estimated by Tafel plot for 0 wt.%-capacitance at 1.5 V vs. RHE and SiO2 were 7.0×10-3 and 0.067 V at 0.01 and 0.4 surface film resistance for the anode A cm-2, respectively. And, those of 5 wt.%-SiO2 prepared with Ir: Ta: Si = 47.5: 47.5: 5 were 0.015 and 0.096 V at 0.01 and 0.4 A cm-2, wt.% precursor etched by various respectively. Therefore, the decrease in surface concentration NaOH(aq) with and

film resistance greatly contributed to the without saturated tantalum (ST) for 5 improvement of electrode property. and 45 h.

These results indicated that the catalyst amount and surface film resistance decreased and the double layer capacitance increased by the NaOH etching. Hence, it need to extend the specific surface area without the consumption of catalyst by the optimizing of etching condition.

ACKNOWLEDGMENTS This research has been supported by Cross-

ministerial Strategic Innovation Promotion Program (SIP) “energy carrier” (Funding agency: JST). The Institute of Advanced Sciences (IAS) in YNU is supported by the Program for Promoting

Fig. 2 Tafel plot for the anodes Reform of National Universities. This research prepared with Ir: Ta: Si = 47.5: 47.5: 5 has been contributed titanium plate treated with or 50: 50: 0 wt.% precursor etched by internal layer by De Nora Permelec Ltd©. We 1.0 M NaOH(aq) for 0 and 45 h.

appreciated person concerned.

REFERENCES [1] K. Nagai, K. Nagasawa, S. Mitsushima, Electrocatalysis, 7, 441, (2016). [2] J.J. Zhang, J.M. Hua, J.Q. Zhang, C.N. Cao, Journal of Hydrogen energy, 36,

5218, (2011). [3] K. Nagasawa, Y. Sawaguchi, A. Kato, Y. Nishiki, S. Mitsushima, Electrocatalysis,

8, 164, (2017). [4] W. Hu, H. Zhong, W. Liang, and S. Chen, ACS Applied Materials & Interfaces, 6,

12729, (2014). [5] S. Xu, S. Chen, L. Tian, Q. Xia, W. Hu, J Solid State Electrochem, 20, 1961,

(2016). [6] L.A. da Silva, V.A. Alves, M.A.P. da Silva, S. Trasatti and J.F.C. Boodtst,

Electrochem. Acta, 42, 272, (1997).

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RELATIONSHIP BETWEEN AMOUNT OF LITHIUM DOPED AND OER OF LIXNI2-XO2/NI FOR ALKALINE WATER ELECTROLYSIS

Xu Yao1, Yoshiyuki Kuroda1, Koichi Matsuzawa1, and Shigenori Mitsushima1,2

1Green Hydrogen Research Center, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan 2Institute of Advanced Sciences, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan E-mail: cel@ml.ynu.ac.jp

Keywords: AWE, OER, Li doped Ni, Thermal decomposition

INTRODUCTION Alkaline water electrolysis (AWE) is a suitable commercial production method for“Green

hydrogen” that is made from water and renewable energy with a simple and less expensive configuration. A conventional AWE anode is a Ni based material which is stable under steady electrolysis[1]; however, Ni is prone to be deteriorated under cycling potential which simulates fluctuating electricity from renewable energies. The durability of a Ni based anode needs improvement. In previous study, we developed a LixNi2-xO2/Ni prepared by thermal decomposition, using several kinds of precursor. The electrode prepared from nickel acetate showed not only high activity but also durability, because a thin layer of dense oxide was formed on the electrode by thermal decomposition and it would suppress the growth of hydrous oxide layer which is less active for OER. Thus far the relationship between anode performance (i.e., activity and durability) and the characteristics of the electrodes (i.e. doped amount of lithium and thickness) is still ambiguous. In this study, the effect of the thickness of LixNi2-xO2 coating on the durability of LixNi2-xO2/Ni anode was investigated.

EXPERIMENTAL A Ni plate (The Nilaco Co., 99+%) was etched in boiling 17.5 % hydrochloric acid for 6 min.

Then, a precursor was painted, dried at 80 oC for 15 min, and thermally decomposed at 550 oC for 15min. The precursor is an aqueous solution of LiNO3 (Wako Pure Chemical Ind. Ltd., 99+%) and Ni(CH3COO)2·4H2O (Junsei Chemical Co. Ltd., 98.0%) with nominal composition of Li : Ni = 0.12 : 1.88 or 0.10 : 1.90 in mole ratio. In order to deposit certain amount of the coating product, painting, drying, and thermal decomposition cycle was repeated for 15 times. Finally, the electrode was calcined at 550 oC for 1h. A Ni coil and a reversible hydrogen electrode (RHE) were used as counter and reference electrodes, respectively. All measurements were performed with three-electrode electrochemical cell at 30oC, using 7.0M (=mol dm-3) of KOH as an electrolyte.

The durability of the anodes was examined by a 20000-cycle potential cycling between 0.5and 1.8 V vs. RHE with the scan rate of 1V s-1. The nickel redox reactions and the OER activity were measured by slow scan voltammetry (SSV) between 0.5 and 1.8 V vs. RHE with the scan rate of 5 mV s-1.

RESULTS AND DISCUSSION Figure 1 shows the IR-free Tafel plots of three LixNi2–xO2/Ni anodes before and after the

20000 cycles durability test. The x value and the coated amount were varied as follows: Li0.1Ni1.9O2 (coated amount: 2.01 mg/cm2), Li0.12Ni1.88O2(A) (2.65 mg/cm2), and Li0.12Ni1.88O2(B) (1.06 mg/cm2). Oxidation peaks between 1.3 and 1.4 V vs. RHE correspond to the Ni(II)/Ni(III) redox reaction (i.e., Ni(OH)2 = NiOOH + H+ + e–) and those around 1.58 V vs. RHE would be due to Ni(III)/Ni(IV) redox reactions. The conversion of Ni(III) to Ni(IV) cause enhancement of

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the electronic resistance and deactivation of the OER[2]. An OER current was observed above these potential regions, and the OER activity was in the order of Li0.1Ni1.9O2 > Li0.12Ni1.88O2(A) ≥ Li0.12Ni1.88O2(B). The order was unchanged before and after the durability test, though the differences in the activity were increased after the durability test. The activity of the Li0.12Ni1.88O2(A) and (B) decreased with the appearance of the oxidation peaks around 1.55 V vs. RHE, it was found after 10,000 cycles. The Li0.1Ni1.9O2 had significantly higher OER activity than the Li0.12Ni1.88O2(A) and (B), and was more durable than others.

Figure 2 illustrates variation of the OER activity at 1.7 V vs. RHE during durability test. Thecurrent density for Li0.1Ni1.9O2 was almost constant during durability test, while current density of the Li0.12Ni1.88O2(A) and (B) represented a peak shape. The electrode was activated up to 1000 cycles, and the OER activity decrease after 1000 cycles. The redox peak of Ni(III)/Ni(IV) appeared after 10000 cycles, and the OER activity is almost the lowest level at this cycle. Formation of Ni(IV) is probably related to the deterioration of the OER activity, even though the difference between Li0.1Ni1.9O2 and Li0.12Ni1.88O2 was not significant. The effect of the Li amount, relative density of the oxide layer or some other factors on the OER activity should be considered to clarify these differences.

Fig. 1 IR-free Tafel plots of the three Fig. 2 initial activities of the three electrodes before and after the 20000-cycle electrodes at 1.7V during the durability potential cycling. test.

ACKNOWLEDGEMENT

THE INSTITUTE OF ADVANCED SCIENCES (IAS) IN YNU IS SUPPORTED BY THEMEXT PROGRAM FOR PROMOTING THE REFORM OF NATIONAL UNIVERSITIES. WE APPRECIATE TO ALL WHO CONCERNED WITH.

REFERENCES [1] Lu, P. W. T., and S. Srinivasan. J. Electrochem. Soc. 125. (1978) 1416–1422 [2] S. Fujita, I. Nagashima, Y. Sunada, Y. Nishiki, and S. Mitsushima, Electrocatalysis

(2017) doi10.1007/s12678-017-0390-x.

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ELECTRODE POTENTIAL MEASUREMENT IN POLYMER ELECTROLYTE MEMBRANE WATER ELECTROLYZER

Naoto Morita1, Kensaku Nagasawa2, Yoshiyuki Kuroda1, Koichi Matsuzawa1 and Shigenori Mitsushima1, 2 1Green Hydrogen Research Center, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan 2Institute of Advanced Sciences, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan E-mail: mitsushima-shigenori-hp@ynu.ac.jp

Keywords: Electrode potential, Liquid junction

INTRODUCTION Polymer electrolyte membrane water electrolysis (PEMWE) has been expected as a

hydrogen production technology combined with renewable energy because of wide operation power range with pure hydrogen production [1]. In order to improve PEMWEs, polarizations of catalyst layers, current correctors, and electrolyte must be identified under high current operation. To evaluate the polarizations, the electrode potential measurement with a reference electrode is essential. To measure an electrode potential, followings are needed for the reference electrode; i. Ionic contact with the same electrolyte as an electrode in interest, ii. The evaluation of iR drop between reference and the electrode [2]. Here, the iR drop evaluation is difficult for membrane electrolysis because of current distribution of edges of electrodes. In this study, a polymer electrolyte membrane (PEM) that had ribs to connect with the

outside was used as ionic conduction between electrolyzer and reference electrode. And the edge effect on the iR drop has been discussed with the structure around the electrode edges to improve evaluation method of the PEMWEs.

EXPERIMENTAL The mixture of IrOx powder (TKK) and

Nafion® 5 wt% solution (DuPont, Nafion: Catalyst = 22: 78 mass) was applied on 5×5 cm-2 of PEM (Nafion®117) as anode catalyst layer at loading of 0.76 mg cm-2 by the decal method [3]. The mixture of Pt-Ru/C (TEC61E54, TKK), Nafion® 5 wt% solution (Nafion: Carbon = 0.8: 1 mass),

Fig. 1 Schematic of electrolyzer structure pure water and 1-propernol was for electrode potential measurements applied on 5×5 cm-2 of a carbon paper at the PtRu loading of 0.5 mg cm-2. Then, the PtRu/C loaded carbon paper and the IrOx loaded PEM were hot-pressed at 0.4 MPa and 120oC for 5 min to fabricate the membrane electrode assembly (MEA). In this process, as shown in Figure 1, the cathode and anode overhung 3 mm against each other at the opposite edge. The ribs of the PEM were connected to a reference electrode (RHE) through 1 M H2SO4 electrolyte. Reference point: k was defined as thickness ratio of the membrane from the overhung side. Therefore, the

k/ -

k/

-

E/

V v

s. R

HE

∆E

/ V

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measured cathode potential contained resistance polarization of k i R, and the measured anode potential contained (1 - k) i R. Here, the rib from the cathode and anode overhanging side are called as cathode and anode liquid junction, respectively. The electrochemical measurements were conducted by linear sweep voltammetry (LSV),

chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). Electrode potential was measured by using each liquid junction.

RESULTS AND DISCUSSION Calculated by ∆EAn.0.15If the cathode and anode junction give

symmetrical polarization of i R each other, ∆ECa.the k is described as following equations.

0 40k = (iR – ΔEAn.)/2iR (1) 30k = (iR – ΔECa.)/2iR (2) 20Here, ΔEAn and ΔECa are difference 10-0.15between the measured anode potentials 0

and cathode potentials using each liquid -100 200 400 600junction, respectively. R was internal i / mA cm-2

resistance between anode and cathode -0.300 200 400 600measured by EIS. i / mA cm-2Figure 2 shows the k as a function of

current density. The k converged to a Fig. 2 Reference point: k as a constant with current increase, and the function of currnt density. average above 200 mA cm-2 was 0.076,

while in the low current density region, 2.4the k is hard to determine because of the small i R as shown in inset.

Figure 3 shows the measured and 1.6120corrected potentials with 0.076 of the k. Difference of EAn.80

The corrected polarization determined 0.8 40 ECa.with the anode and the cathode junction 00 200 400 600showed almost same curves. The inset

i / mA cm-2shows the difference of the corrected 0potentials with anode and cathode junctions. The differences decreased with -0.8the increase of current density. Above 0 200 400 600400 mA cm-2, the difference was smaller i / mA cm-2than 50 mV. In practical use, Circle: Anode liquid junctionimprovement of water electrolyzer

Triangle: Cathode liquid junctionperformance in high current density is Experimental datasignificantly essential, so this electrode

potential measurement should be useful iR freein development.

Fig. 3 Polarization curves and difference of corrected anode and cathode potential curves.

REFERENCES [1] M. Carmo, D. L. Fritz, J. Mergel and D. Stolten, Int. J. Hydrogen Energy, 38,

4901-4934 (2013) [2] P. Piela, T. E. Springer, J. Davey, and P. Zelenay, J. Phys. Chem. C, 111, 6512-

6523 (2007) [3] M. S. Wilson and S. Gottesfeld, J. Appl Electrochem., 22, 1-7 (1992)

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PREPARATION OF POROUS NB-DOPED TITANIUM OXIDE USING A COLLOIDAL CRYSTAL TEMPLATE FOR CATALYST SUPPORTS

Hirotaka Kajima1, Hikaru Igarashi1, Yoshiyuki Kuroda1, Koichi Matsuzawa1, Akimitsu Ishihara2 and Shigenori Mitsushima1,2

1Green Hydrogen Research Center, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan 2Institute of Advanced Sciences, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan cel@ml.ynu.ac.jp

Keywords: conducting oxides, Nb-doped titanium oxide, mesoporous materials

38BINTRODUCTION One of the most important demands on electrodes used for fuel cells and industrial

electrolysis is high durability under operation conditions. For example, a carbon black is degraded under high anodic potential and high temperature. Recently, conductive metal oxides, such as Nb-doped TiO2 and Ti4O7, have attracted much attention because of their high durability.[1] Ordered porous materials have large specific surface area and uniform diffusion path. If porous materials are synthesized by using conductive oxides, they are promising as catalyst supports. We have reported the synthesis of mesoporous Ti4O7 by replicating a mesoporous silica template (SBA-15); however, a reduction treatment at high temperature (typically at more than 700°C) tends to cause collapse of nanostructures. Therefore, it is important to synthesize conductive oxides under mild conditions. Here, we focus on the synthesis of Nb-doped TiO2 by using the hydrothermal process, using a silica colloidal crystal as a template. Kitahara et al. reported the synthesis of mesoporous Nb-doped TiO2 by replicating a silica colloidal crystal.[2] A seed of titanium oxide was preliminary introduced in the template, which is an important point for both highly ordered structure and single-crystalline framework. It is important to increase pore sizes to facilitate diffusion of electrolytes and gases for their use as electrochemical devices; therefore, silica nanoparticles with larger size than those in the previous report[2] were used in this study as templates.

EXPERIMENTAL A silica colloidal crystal, consisting of silica nanoparticles 60 nm in diameter, according

to the literature by Yokoi et al.[3] Ti species, which acts as a seed of single-crystalline TiO2 framework, were added into the silica colloidal crystal prior to the hydrothermal deposition of Nb-doped TiO2. The silica colloidal crystal was immersed in a 15 mmol dm-3 TiCl4 solution containing 0.54 mmol dm-3 HCl at 70°C for 1 h. The Ti-containing silica colloidal crystal was filtrated and calcined at 550°C for 30 min. Then, Nb-doped TiO2 was deposited within the Ti-containing silica colloidal crystal by the hydrothermal method in a solution of tetrabutoxytitanium (TBOT, 37 mmol dm-3), NbCl5 (0.84 μmol dm-3), and HCl (16 mol dm-3) at 150°C for 12 h. The amount of Nb was 2mol% with respect to that of Ti. The silica tremplate was removed in 2 mol dm-3 NaOH solution at 80°C for 2 h.

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RESULT AND DISCUSSION A silica colloidal crystal, consisting of silica

nanoparticles ca. 60 nm in diameter was prepared by stepwise growth of silica nanoparticles. Silica nanoparticles ca. 15 nm in diameter were synthesized by the hydrolysis and condensation of tetraethoxysilane (TEOS) in water, using L-lysine as a catalyst. The nanoparticles were then grown to ca. 30 nm in another

Fig. 1. SEM image of silica colloidal solution containing TEOS and L-lysine, and this process crystals (particle size 60 nm). was repeated to obtain silica nanoparticles ca. 60 nm in

size. The concentration of TEOS was controlled below 0.336 mol dm–3 to avoid the nucleation of additional silica nanoparticles. The dispersion of the silica nanoparticles ca. 60 nm in diameter was evaporated, and then a colloidal crystal was obtained by self-assembly of the nanoparticles (Fig. 1). From the N2 adsorption–desorption measurement of the colloidal crystal, the BET specific surface area was 63 m2 g-1 and the total pore volume was

Fig. 2. SEM image of Synthesis 0.192 cm3 g-1 at relative pressure of 0.95. Assuming spherical silica nanoparticle with the density of 2.2 g cm–3, the calculated BET surface area is 45 m2 g-1 which is somewhat smaller than the result. The difference may be due to surface roughness. The calculated total pore volume is 30% which is similar to the theoretical interstices (26%) of the fcc structure.

Mesoporous Nb-doped TiO2 was prepared by the hydrothermal deposition and subsequent removal of the template. The XRD pattern of the product shows that the formation of both rutile and anatase phases. The lattice constants of the rutile phase were calculated to be a=4.59 Å and c=2.95 Å. These values were comparable to those from the JCPDS card (#084-1283, a=4.593 Å, b=2.959 Å). On the other hand, the lattice constants of the anatase phase were calculated to be a=3.80 Å and c=9.56 Å. These values were larger than those from the JCPDS card (#021-1272, a=3.785 Å, b=9.5139 Å), which suggests the substitution of Ti4+ with Nb5+.[2] The SEM image (Fig. 2) of the product shows that some oxide particles possessed uniform spherical pores on the surface. Such pores should be formed by replicating the colloidal crystal template, though the oxide was suggested to be deposited on the outer surface of the template. In conclusions, porous TiO2 which may incorporate Nb atoms was partially obtained by using a colloidal crystal template consisting of silica nanoparticles ca. 60 nm in size as a template.

ACKNOWLEDGEMENTS We are grateful to Prof. Kazuyuki Kuroda and Mr. Yuta Shimasaki for their advice on

the synthetic methods. This work was supported by Grant-in-Aid for Scientific Research (17K06803).

REFERENCES [1] T. Ioroi, Z. Siroma, N. Fujiwara, S.Yamazaki, K. Yasuda, Electrochem. Commun., Vol. 7 (2005), p. 183-188. [2] M. Kitahara, Y. Shimasaki, T. Mastuno, Y. Kuroda, A. Shimojima, H. Wada, K. Kuroda, Chem. Eur. J., 21, 13073 (2015) [3] T. Yokoi, Y. Sakamoto, O. Terasaki, Y. Kubota, T. Okubo, T. Tasumi, J. Am. Chem. Soc., 128, 13664-13665 (2006)

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Oral Presenters

Prof. Yoshiyuki Kuroda, Yokohama National University

Dr. Cordellia Sita, University of the Western Cape

Registered Participants

Sebastian Bock, Graz University of Technology, Austria

Kurt Mayer, Graz University of Technology, Austria

Verena Martschitsch, Graz University of Technology, Austria

Johanna Ranninger, Graz University of Technology, Austria

Katharina Kocher, Graz University of Technology, Austria

Turgay Koroglu, Graz University of Technology, Austria

Rachinger Michael, Graz University of Technology, Austria

Gasteoger Marika Natalie, Graz University of Technology, Austria

Zhao Yun, Graz University of Technology, Austria

Poimer Florian, Graz University of Technology, Austria

Rauh Julius Frederik, Graz University of Technology, Austria

Fruehwirt Philipp, Graz University of Technology, Austria

Hofstetter Martin, Graz University of Technology, Austria

Domijanic Marko, Graz University of Technology, Austria

Brunner Helmut, Graz University of Technology, Austria

Ladreiter Walter, Graz University of Technology, Austria

Schranger Horst, Graz University of Technology, Austria

Penga Zeljko, University of Split, Croatia

Pivac Ivan, University of Split, Croatia

Pivac Nikolina, University of Split, Croatia

Wasif Danish Muhammad, Forman Christian College University, Pakistan

Suthida Authayanun, Srinakharinwirot University, Thailand

Wang Lida, Yokohama National University, Japan

Hikaru Igarashi, Yokohama National University, Japan

Keisuke Tanimoto, Yokohama National University, Japan

Masayuki Nagai, Yokohama National University, Japan

Yongbin Ma, Yokohama National University, Japan

Yudai Tsukada, Yokohama National University, Japan

Tsubasa Tokai, Yokohama National University, Japan

Kaoru Nagano, Yokohama National University, Japan

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Konosuke Watanabe, Yokohama National University, Japan

Atsushi Maeda, Yokohama National University, Japan

Satoshi Nishimura, Yokohama National University, Japan

Noriyoshi Hasegawa, Yokohama National University, Japan

Yusuke Tamada, Yokohama National University, Japan

Kohei Maniwa, Yokohama National University, Japan

Xu Yao, Yokohama National University, Japan

Naoto Morita, Yokohama National University, Japan

Hirotaka Kajima, Yokohama National University, Japan

Bao Yun, Yokohama National University, Japan

Misu Takehiro, Yokohama National University, Japan

Koike Junpei, Yokohama National University, Japan

Shimabukuro Wataru, Yokohama National University, Japan

Sumi Kyogo, Yokohama National University, Japan

Hino Soki, Yokohama National University, Japan

Hirata Junji, Yokohama National University, Japan

Masumura Haruki, Yokohama National University, Japan

Thibault Rafaideen, Yokohama National University, Japan

Inoue Shoki, Yokohama National University, Japan

Shimosawa Kohei, Yokohama National University, Japan

Hamada Koshi, Yokohama National University, Japan

Minami Ryotaro, Yokohama National University, Japan

Kitagawa Yuya, Yokohama National University, Japan

Shigemasa Kaito, Yokohama National University, Japan

Hashimura Sota, Yokohama National University, Japan

Otsuki Yota, Yokohama National University, Japan

Kawamura Toshiki, Yokohama National University, Japan

Akiyama Mio, Yokohama National University, Japan

Hoque Mahfuzul, Yokohama National University, Japan