Fuel Cell Research at the University of South Carolinamechanical properties& structural integrity ( Ductility, hardness, stress relaxation, stress-strain law, Overall seal performance;

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John W. Van ZeeUniversity of South Carolina

Columbia, SC

Fuel Cell Research at the

University of South Carolina

Project ID #FC47

2 FC47, DOE Program Review, June 2008

Overview

• Start - Feb 2007• Finish – Dec 2008• Percent complete - 65%

• Barriers addressed• A - Durability• B - Cost• C - Performance

• Total project funding -$2,068,750• DOE - $1,655,000• Contractor - $ 413,750

• Funding received in FY06 - $0• Funding for FY07 - $ 886,607• Funding for FY08 - $1,182,144

Budget

• Interactions/ collaborations • 14 Companies of NSF I/UCRC

Center for Fuel Cells• DOE H2 Quality Team • Plug Power

Partners

Timeline Barriers


Project 1- Non Carbon Supported Catalysts• Develop novel materials (e.g., Nb doped) for

• improved corrosion resistance• improved fuel cell components

Project 2 -Hydrogen Quality• Develop a fundamental understanding of

• performance loss induced by fuel contaminants• durability loss fuel induced by contaminants

Project 3 -Gaskets for PEMFCs • Develop a fundamental understanding of

• the degradation mechanisms of existing gaskets • the performance of improved materials

Project 4 -Acid Loss in PBI-type High Temperature Membranes• Develop a fundamental understanding of

• acid loss and acid transport mechanisms• Predict performance and lifetime as a function of load cycle

OBJECTIVES


Task 1. Development of Titania-based Non-carbon SupportsSubtask 1.1 Synthesis of high surface area Nb doped TiO2Subtask 1.2 Synthesis of high surface area Ti4O7 supportsSubtask 1.3 Deposit catalysts – Form electrodes

Task 2. Characterization of the Developed Supports & CatalystsSurface and Spectroscopy Methods:

(BET, Porosimetry, SEM, TEM, XRD, TGA, XPS, XAS)

Task 3. Electrochemical CharacterizationTask 4. Corrosion Studies on Developed Supports & CatalystsTask 5. Stability Analysis of the Loaded Catalysts with ADT

(ADT = accelerated durability test)

Task 6. Industrial Interaction and Presentations

Approach: Project 1: Non Carbon Supported Catalysts


Conductivity of Nb-Doped TiO2 Support

10 15 20 25 30 35 40

1E-5

1E-4

1E-3

0.01

0.1

Con

duct

ivity

(ohm

-1cm

-1)

Nb content (at.%)0 200 400 600 800 1000

1E-5

1E-4

1E-3

0.01

0.1

Con

duct

ivity

(ohm

-1cm

-1)

Heat treatment temperature (oC)

• The electrical conductivity shows a maximum for 25 at% Nb and 700 oC.

• Increase in conductivity is due to the presence of Ti3+ and Nb2+.

Project 1: Technical Accomplishments/Progress/Results


Pt Catalyst Supported on Nb-Doped TiO2

-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4-0.20

-0.15

-0.10

-0.05

0.00

0.05

0.10

Pt/C (E-Tek)

Pt/Nb-TiO2

Cur

rent

(mA

)

Potential (V) vs. NHE

The electrochemical active surface area (ECSA) of Pt/Nb-TiO2 is comparable to that of Pt/C.

Electrolyte: 0.5 M H2SO4Sweep rate: 5 mV/sCatalyst loading: 246 µg/cm2 (Pt/Nb-TiO2)

120 µg/cm2 (Pt/C)



0.0 0.2 0.4 0.6 0.8 1.0 1.2-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

Cur

rent

den

sity

(mA/

cm2 )

Potential (V) NHE

82 μg/cm2

164 μg/cm2

246 μg/cm2

328 μg/cm2

492 μg/cm2

Electrolyte: 0.5 M H2SO4Scan rate: 5 mV/s

0.2 0.4 0.6 0.80

1

2

3

4

5

% H

2O2

Potential (V) NHE

82 μg/cm2

164 μg/cm2

246 μg/cm2

328 μg/cm2

492 μg/cm2

• The catalytic activity of Pt/Nb-TiO2 is comparable to that of Pt/C.

• The catalyst produces less than 4% H2O2.

Project 1: Technical Accomplishments/Progress/ResultsPt/Nb-TiO2 : LSV - Effect of Loading


B. L. García, R. Fuentes, and J. W. Weidner, Electrochem. and Solid-State Letters, 10 (7) B108.

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 50 100 150 200 250 300 350 400

Current Density (mA/cm2)

Cel

l Vol

tage

(V)

Pt-Ru/Nb-TiO2

Pt-Ru/C (Commercial E-Tek Electrode)Flow A/C = 20 sccm / 20 stoichLoadings A/C = 3 / 2 mg/cm2

Project 1: Technical Accomplishments/Progress/ResultsOpportunities for DMFC


A Nb-doped TiO2 support with high surface area and electrical

conductivity was developed by using a hydrothermal process.

The synthesized support has a mesoporous structure and a surface area

of approximately 80 - 150 m2 g-1, which is much higher than that

reported in the literature.

Initial tests indicate low corrosion and comparable polarization for the

ORR

Initial tests indicate high turnover frequency for MeOH oxidation

Summary Project 1: Technical Accomplishments


Task 1. Group Contaminants by Probable Mechanism (Adsorption/Desorption, Reactive, Transport Through MEA)

Task 2. Study Effect of Temperature DistributionsSubtask 1.1 Predict temperatures in common cellsSubtask 1.2 Design new laboratory cellsSubtask 1.3 Measure temperature distributions

Task 3. Design & Perform Experiments by MechanismSub Task 3.1 Determine independent adsorption isotherms and rate constants (for CO, a marker compound, as agreed by H2 quality team) Sub Task 3.2 Extend the methodology to other species

Task 4. Predict Long-term Effects Task 5. Exploratory Study with ORNL: Intra-PEMFC Sensors (see Additional Slides)Task 6. Interact with H2 Quality Team Task 7. Presentations of Results

Approach: Project 2: Hydrogen Quality


Provide data on Gore 57 Series MEAsSuitable for comparison with other MEAs & loadingsOver an operating range that allows parameter estimationComplementary to other groups & modeling effortProvide fundamental parameters for ANL’s recirculation model

Contribute data & techniques to the H2 Quality Team ModelANL model (R. K. Ahluwalia, X. Wang, J. Power Sources, 162 (2006) 502, 171 (2007) 63, 180 (2008) 122)

Approach: Project 2: Hydrogen Quality- Task 3


Obtain Polarization & Anode Overpotential data:Operating conditions:

Tcell = 80 ◦C and 60 ◦CBack pressure = 0/0 psig and 25/25 psigRelative humidity = 75/25 % RH (A/C)Stoic ratio = 1.2/2.0

Pco = 10, 25, 50, 100 ppm - completePco = 0.2, 1.0, 2.5 ppm – in progressO2 crossover (internal air bleed) – in progress

Determine isotherms and rate constants from these data

Approach: Project 2: Hydrogen Quality- Task 3In-situ Experimental Data for CO Poisoning Characterization


Fig. 2.1 Hysteresis profiles for CO at 10, 25 and 50 ppm with 20 minutes of holding time.(Tcell = 80 C, back pressure = 0/0 psig)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 200 400 600 800 1000 1200 1400

i (mAcm-2)

Pote

ntia

l (V

)

50 ppm

25 ppm

10 ppm

Up

Down


Figure 2.2. Current density versus time for 25 ppm CO at potential = 0.30, 0.55 and 0.70, scanning up-down until reaching steady state.

0

200

400

600

800

1000

1200

0 1 2 3 4 5 6 7 8 9 10 11

Time (Hrs)

i (m

Acm

-2)

0.30 V

0.55 V

0.70 Vscan up

scan down

0.70 --> 0.55 Longer time for scan down


Fig. 2.3. Polarization with CO for Tcell = 80◦ C & 0 psig.

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 200 400 600 800 1000 1200 1400 1600 1800 2000

i (mAcm-2)

Pot

entia

l (V

)

Base line

10 ppm25 ppm

50 ppm100 ppm


0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 200 400 600 800 1000 1200 1400 1600

i (mAcm-2)

ηa (

V)

10 ppm

25 ppm

50 ppm100 ppm

Fig. 2.4. Anode overpotential for CO at 80◦ C & 0 psig.


0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 200 400 600 800 1000 1200 1400 1600 1800 2000

i (mAcm-2)

ηa (

V)

50 ppm

10 ppm

25 ppm

100 ppm10 ppm

80 C, 25 psig60 C, 25 psig

25 ppm

Fig. 2.5. Temperature dependence of anode overpotential at 25 psig.


Figure 11

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 200 400 600 800 1000 1200 1400 1600 1800 2000

i (mAcm-2)

ηa (

V)

50 ppm

10 ppm

25 ppm

100 ppm

10 ppm

50 ppm

0 psig, 80 C

25 psig, 80 C

25 ppm

100 ppm

Fig. 2.6. Pressure dependence of anode overpotential at 80 C



• Provided data on Gore 57 Series MEAs• Suitable for comparison with other MEAs & loadings• Over an operating range that allows parameter estimation• Complementary to other groups & modeling effort• Data for lower concentrations - in progress• Consistent set of parameters for this MEA – in progress

• Future Work • Develop techniques to understand the effect of loading • Extend methodology to other contaminants (NH3 & H2S)• Develop consistent methodology for obtaining parameters• Continue to interact with H2 Quality team


Task 1. Selection of Commercially Available Seal Materials. (95 % complete)

Task 2. Aging of Seal Materials In simulated and accelerated FC environmentWith and without stress/deformation

Task 3. Characterization of Chemical StabilityPerform both constant stress & constant displacement tests Assess the effect of applied stress/deformation on the rate of degradation Measure chemical/thermal stability will be assessed by various

Task 4. Characterization of Mechanical Stability

Task 5. Development of Accelerated Life Testing Procedures

Task 6. Industrial Interaction and Presentations

Approach: Project 3- Gaskets for PEMFCs


Pressure

Temperature

Chemicals

Gasket or Seal

Characteristics of gasket/seal :

Under compression, exposed to chemicals, high temperature, pressure, cyclic conditions, etc.

Loss of functionality : by cracking and /or stress relaxation

Cracking : due to corrosion under compression (Chemical stability)

Stress Relaxation : material degradation… loss its sealing ability (mechanical stability)

Leachants: detrimental sometimes (chemical stability)

Ambient

Approach: Project #3: Gasket/Seal as a structural member in Fuel Cells

Interior


Aging in simulated/acceleratedfuel cell environment(temperature, solutions, stress/deformation)

Characterization of chemical stability:

(SEM, XPS, ATR/FTIR, AtomicAdsorption S pectrometer

Characterization of mechanical properties & structural integrity

( Ductility, hardness, stress relaxation, stress-strain law,

Overall seal performance;

Solvent swelling )

TGA/MS

Microindentation,DMA)

Service life prediction

Accelerated life test methodology;

Failure model;Material selection /

development products

Approach: Project #3: Flow Chart of Studies


From Company 1 From Company 2

Materials studied

liquid silicone elastomer(DLS),

Fluorosilicone rubber(DFS),

copolymeric resin(DC)

EPDM,

Fluoroelastomer(FKM)

ADT, Regular solution ADT, Regular solution

Test temperature:80°C Test temperature:80°C



Labels for samples from Company # 1

• In ADT solution(accelerated durability test)

• A-DLSA-DFSA-DC

• In regular solution

• R-DLS• R-DFS• R-DC


Weight loss and chemical leaching

• A-DLS, A-DC and R-DLS→ more weight Loss and more Si leaching →Lost Si is the cause of weight loss

• No detectable Mg in all silicone elastomer• The amount of Ca is in the range of 0-5mg/l• The amount of Si is in the range of 5-300 mg/l

Si

0.0

50.0

100.0

150.0

200.0

250.0

300.0

0 10 20 30

Time (Weeks)

Leac

hant

s (m

g/l) A-DLS

A-DC

R-DLS

A-DFS

R-DFS

R-DC

A-DLS

A-DC

R-DLS

-30-25

-20-15-10

-50

0 10 20 30

Time (weeks)

Wei

ght L

oss

(%) A-DFS

R-DFSR-DCR-DLSA-DLSA-DC

A-DC

A-DLS



Optical image of DLS and DC before and after exposure to ADT solution for 10 weeks

10 μm

10 μm

10 μm 10 μm

DLS-after

DC-after

Crystal-likeaccumulation

DLS-before

DC-before


Project # 3: ATR-FTIR for DLS

ADT

Regular

Chemical changes in backbone and crosslinkeddomain after 3week exposure

No significant Chemical Changes after 15 week exposure


Elastic modulus E’ and Tan δ for DC exposed to ADT solution (by DMA)

1.E-04

1.E-02

2.E-02

3.E-02

4.E-02

5.E-02

6.E-02

7.E-02

8.E-02

9.E-02

-80 -30 20 70 120

Temperature (°C)

Tan

δ

DC-A-0WDC-A-4WDC-A-10WDC-A-15WDC-A-25W

1.E+05

1.E+06

1.E+07

1.E+08

1.E+09

-80 -30 20 70 120

Temperature (°C)

E' (P

a)

DC-A-0WDC-A-4WDC-A-10WDC-A-15WDC-A-25W

1. E’ gradually decrease over time, especially at 25W (weeks) exposure2. Tg remains at -47°C ± 1 °C3. Constant oscillation after glass transition temperature for the loss modulus

curves and Tan δ curves.


Compression Stress Relaxation curves of DLS at different temperature and different medium

•A combination of DI water and high temperature results in dramatic reduction of the retained seal force

•Acidic solution has minimal effect compared to water

Water,70Regular,70

Water,100



1. Optical microscope and ESEM analysis to examine the degradation of surface. 2. ATR-FTIR test to elucidate the material surface chemical degradation.3. Atomic adsorption spectrometry analysis to identify leachants from seals

into the soaking solutions.4. Microindentation test for assessing the mechanical properties of the gasket

materials. 5. New equipment purchased:

a. DMA for assessing the dynamical mechanical properties of the gasketmaterials.

b. Compression Stress relaxation test system to monitor the retained seal force under fuel cell condition

6. Developing life prediction methodologies.7. Publications in Journal and Conferences and discussions with members in the

Center for Fuel Cells.


Approach: Project 4 - Acid Loss in PBI-type High Temp. Membranes (interaction with Plug Power)

Task 1. Exercise Existing Computer Code(a) over a range of operating conditions (b) to determine model limitations(c) to compare predictions/behavior with existing data. (d) propose experiments required to improve the model

Task 2. Additional Experiments and Model Modification(a) obtain data for water content as f ( T, Dew point)(b) obtain data for water & acid balance as f ( T) under load

Task 3. Presentations and Publication


0

10

20

30

40

50

60

70

80

0 1000 2000 3000 4000 5000 6000 7000 8000

time (hr)

Wei

ght %

H3P

O4

I = 0.02 A/cm2I = 0.1 A/cm2I = 0.2 A/cm2I = 0.4 A/cm2I = 0.8 A/cm2

Project 4: Technical Accomplishments/Progress/Results:Change of wt % depends on water/membrane equilibrium

(Predictions below assume all water remains in MEA-unlikely but how much?)


1. Obtained where .

2. Measured acid loss to gas stream at open circuit.

3. Report and analyze weight change data relative to dry membrane mass.

( )TPf OH ,2

=λ43__

__POHofmoles

waterofmoles=λ


Experimental ConditionsTemperatures: 160 ºC to 90 ºC

Sample size (nominal): 1 inch² (6.4516 cm²)Total nitrogen flow: 500 sccm,Water partial pressure scanning rate: 0.01 to 0.002 (kPa/101kPa/min)


Figure 4.2. Schematic experimental setup to measure water euilibrium.

MEA

UHP N2

UHP N2

Mass Flow Controller

Mass Flow Controller

Heater

Heater

Humidifier

Load Cell

Wire

Stream #1

Stream #2

Stream #1+#2

Heated Tubing

T/CT/C

T/C

PH Sensor

Water Collector


Container Temperature: 160 oC; Switching time: @20th minute Initial humidity: 0.020,17.5 oC dew pointFinal humidity: 0.156,55 oC dew point

0.54

0.542

0.544

0.546

0.548

0.55

0 20 40 60 80 100

Time (min)

Wei

ght (

G)

Project 4: Technical Accomplishments/Progress/ResultsResponse of water absorption into the MEA with step change in inlet humidity.


Figure 4.4A. Change of lambda (mol fraction of water/phosphoric acid) with dimensionless water vapor pressure.

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 0.2 0.4 0.6 0.8 1

Water Vapor Pressure/101.3 KPa

λ m

ole

H2O

/mol

e H

3PO

4

125 ºC 0.01/min

160 ºC 0.01/min

90 ºC 0.002 bar/min

100 ºC 0.002 bar/min

Suspected acid leach0.69Psat

CO,90H2=°



Figure 4.4B. Change of λ (mole of water/mole of phosphoric acid) with temperature.

0

1

2

3

4

60 80 100 120 140 160 180

Temperature ºC

Lam

da

5.02

=OHP

4.03.0

2.0

1.0


38 DOE Program Review, June 2008 FC47 University of South Carolina


Task 1. Exercise of Computer Code showed that (a) data obtained for water content as f ( T, Dew point) (b) data need for water balance as f ( T) under load (c) data needed for cathode carbon corrosion (d) data needed for transient experiments

Task 2. Experiments and Model ModificationSubtask 2.1 – water content data obtainedSubtask 2.2 – water balance experiments underwaySubtask 2.3 - transient experiments underway

39 DOE Program Review, June 2008 FC47 University of South Carolina

Project 1: B. N. Popov, J. W. Weidner

Project 2: J. St-Pierre, T. GuSpaci-MS: ORNL: T. J. Toops, W. P. Partridge

Project 3: Y. J. Chao, C. T. Williams, Company Reps. NSF- Center for Fuel Cells

Project 4: S. Shimpalee, T. GuPlug Power: B. Du, R. Pollard

Acknowledgements (Senior Collaborators)

Documents

Fuel Cell Research at the University of South Carolinamechanical properties& structural integrity ( Ductility, hardness, stress relaxation, stress-strain law, Overall seal performance;