Sep. 20, 2006 Ph.D., Seminar - II T. Maiyalagan CYD01006 Electro-catalytic supports for noble metals for exploitation as electrodes for fuel cells

Sep. 20, 2006

Ph.D., Seminar - II

T. MaiyalaganT. MaiyalaganCYD01006CYD01006

Electro-catalytic supports for noble metals Electro-catalytic supports for noble metals for exploitation as electrodes for fuel cellsfor exploitation as electrodes for fuel cells

http://www.iitm.ac.in/

IntroductionIntroduction

Principle of DMFCPrinciple of DMFC

Role of supports in electrocatalystRole of supports in electrocatalyst

Nitrogen containing carbon nanotubesNitrogen containing carbon nanotubes

Metal oxide nanomaterials (TiOMetal oxide nanomaterials (TiO2 2 nanotubesnanotubes & WO& WO33 nanorods) nanorods)

Conducting polymer nanotubules and polymer -metal oxide Conducting polymer nanotubules and polymer -metal oxide

nanocomposite (PEDOT–Vnanocomposite (PEDOT–V22OO5 5 ))

ConclusionConclusion

1OutlineOutline

Thermal energy-conversion Mechanical energy-conversion

Fuel cellElectrical energy-conversion

I.C.E

Chemical energy of the fuel

C. K. Dyer, J. Power. Sources, 106 (2002) 245

Direct Energy Conversion Vs Indirect Technology

What are fuel cells ?What are fuel cells ?

AFC (Alkaline)

SPFC (PEM) (Solid

Polymer)

DMFC (Direct

Methanol)

PAFC (Phosphoric

Acid)

MCFC (Molten

carbonate)

SOFC (Solid Ox-

ide)

Operation temp. [°C] 80 40-80 60-130 200 650 1000

Fuel (1) H2 H2 (CO2) Methanol H2 (CO2) H2, CO H2,CO,CH4

Electrolyte material KOH Polymer Polymer Phosferic Acid

Molten Car-bonate

Solid Oxide

Typical applications Space (transport)

Transport & CHP(2).

Mobile phones &

laptop PC’s.

CHP(2) CHP(2) CHP(2)

(1) Fuel cells accepting mixtures of H2 & CO2 can in combination with a reformer also use all gen-eral hydrocarbons.

(2) Combined Heat & Power production.

Research area

Methanol Fuel Cells

Indirect methanol fuel cell

Direct methanol fuel cell

Fuel : Methanol Fuel : Hydrogen

(Reformed from methanol)Fuel reformer makes the system bulky

Various types of fuel cellsVarious types of fuel cells

Direct Methanol Fuel Cell DMFC advantages More environmentally friendly

High efficiency

Low temperature (60-130 0 C)

Long membrane lifetime

Methanol is safe to store and

distribute than hydrogen

Low emission future power sources

Heinzel et al, J. Power Sources 105 (2002) 250

Catalyst poisoning

Pt-CO

Anode: CH3OH + H2O CO2 + 6H+ + 6e- E = 0.016 V (RHE)Cathode: 3/2O2 + 6H+ + 6e- 3 H2O

E = 1.229 V (RHE)

Overall : CH3OH + 3/2O2 CO2 + 2H2O E = 1.213 V (RHE)

Direct Methanol Fuel Cell (DMFC)Direct Methanol Fuel Cell (DMFC)

To reduce the amount of noble metal loading in the electrodes

Increase metal dispersion on suitable electronically conducting supports

Dispersion Utilization Stability

REDUCTION OF PLATINUM LOADINGS

ObjectiveObjective

High Temperature

Role of support ?

High Temperature

Unsupported catalystUnsupported catalyst

Supported catalystSupported catalyst

Why supported catalyst?Why supported catalyst?

High surface-to-volume ratios

High dispersion of noble metal particles to reduce

noble metal loadings

Avoid the agglomeration of the metal particles in

operation,

Good stability of electrocatalysts

Improved the activity of electro-catalysts through the

interaction between metal and support

Lower the resistance of mass transportation

Always superior to respective unsupported and

conventional supported systems

Shorten the time of DMFC commercialization

Role of electro-catalyst supportsRole of electro-catalyst supports

Interactions between the noble metal and the support may lead to increase catalyst performance

Metal catalysts

Electrocatalyst supportsUnsupported

Poor performance, not economical

Metal oxides Conducting polymers

StabilityIncrease in metal dispersion,

Economical

Carbon nanotubes

TiO2, WO3

nanomaterials

Conducting polymer nanotubes, Polymer- metal oxide nanocomposite

Nitrogen containingcarbon nanotubes

StrategyStrategy

Carbon nanotube as an Carbon nanotube as an electrode support in fuel electrode support in fuel cellscells

• Mesoporosity (2-50nm)• Improved mass transfer• Better dispersion• Surface bound groups• High accessible surface

area• High purity → avoids self-

poisoning• Good electronic

conductivity

Why carbon materials are used Why carbon materials are used as an electrocatalyst support ?as an electrocatalyst support ?

• Electrochemical properties - wide electrochemical potential window

• Chemical properties - Good corrosion resistance

• Electrical properties - Good conductivity

• Mechanical properties - Dimensional & mechanical stability - Light weight & adequate strength

Role of nitrogen on the carbon Role of nitrogen on the carbon nanotube nanotube supported anodes for methanol oxidationsupported anodes for methanol oxidation

Electrode Methanol oxidation

potential at +50 mA/cm2 (V)

Untreated (U) 604

Nitrogen functionalized (N)

554

Sulfur functionalized (S) 633

S.C. Roy et al., J. Electrochem. Soc., 144 (1997) 2323

Nitrogen functionalization in carbon Nitrogen functionalization in carbon supportsupport

Current – potential curve for sulfur functionalized (S), nitrogen functionalized (N) and un-functionalized (U) carbon supports

Pt bound strongly to nitrogen sites so higher dispersion, avoids sintering

Addition of nitrogen increases the conductivity of the material by raising the Fermi level towards the conduction band

The presence of nitrogen generates catalytic site and this catalytic site is responsible for increased activity of methanol oxidation

Pt Pt

carbon

oxygen

hydrogen

+

ê

+

ê

+

ê

+

ê

+

ê

+

ê

e-e- e-e-

Nitrogen induces catalytic activityNitrogen induces catalytic activity

PVPN=12.9%

PPYN=21.2%

PVIN=33.0%

PPP N= 0%

Present workPresent work

NITROGEN CONTAINING POLYMERS

Synthesis of Nitrogen containing carbon Synthesis of Nitrogen containing carbon nanotubesnanotubes

AlCl3(0.5M),CuCl2 Benzene (1M)

Polymerization, RT , 3h

Carbonization, Ar atm

48% HF, 24 h

Alumina membrane

PPP/alumina

CNT/alumina

CNTPPP

Synthesis of CNT from poly(paraphenylene)Synthesis of CNT from poly(paraphenylene)

Cyclic Voltammograms in 1 M H2SO4 aqueous solution at (a) Glassy carbon coated carbon nanotube electrode (b) Glassy carbon coated Vulcan electrode (c) Glassy carbon.

Electrochemical studiesElectrochemical studies

73mM H2PtCl6

12 h

H2 atm,

823 K, 3 h

48% HF,24 h

Loading of catalyst inside nanotubesLoading of catalyst inside nanotubes

Cyclic Voltammograms of (c) GC/CNTppp-Pt--Nafion Nafion in 1 M H2SO4/1 M CH3OH run at 50 mV/s

Electrocatalytic activity of the catalystElectrocatalytic activity of the catalyst


48% HF, 24 h

Poly(vinylpyrolidone) in dichloromethane

PVP/alumina

Alumina membrane

CNTPVP

Synthesis of N-CNTs from Poly(vinylpyrolidone)Synthesis of N-CNTs from Poly(vinylpyrolidone)

SEMSEM

TEMTEM

AFMAFM

T. Maiyalagan, B.Viswanathan, Mater.Chem.Phys , 93 (2005) 291

XPSXPS

Cyclic Voltammograms of (a) GC/CNTppp-Pt-Nafion Nafion in 1 M H2SO4/1 MCH3OH run at 50 mV/s

T. Maiyalagan, B. Viswanathan, U.V. Varadaraju, Electrochem. Commun. 7 (2005) 905

FeCl36H2O(0.2M)

PTSA (0.2 M)

Pyrrole (0.1M)

Alumina membrane

Polymerization, RT , 3h


48% HF, 24 h

PPY/alumina

CNTPPY

Synthesis of N-CNTs from Poly(pyrrole)Synthesis of N-CNTs from Poly(pyrrole)

(d)TEM: Pt/N-CNT

SEM: N-CNT

Vinyl imidazole (0.1m)

AIBN

Benzene

Alumina membrane

Polymerization , 68o C, 10 h


48% HF, 24 h

CNTPVI

PVI/alumina

CNT/alumina

Synthesis of N-CNTs from Poly(vinylimidazole)Synthesis of N-CNTs from Poly(vinylimidazole)

Calculated from polymer Calculated from

carbon nanotubes

SAMPLE % C % N % H % C % N % H

PPP-CNT 93.0 0.0 4.9 92.3 0.0 1.8

PVP-CNT 64.8 12.6 8.2 87.0 6.6 0.8

PPY-CNT 66.7 21.2 6.1 78.2 10.3 0.6

PVI-CNT 63.8 29.8 6.4 75.5 18.9 0.6

Elemental analysis (CHN)Elemental analysis (CHN)

Electrode Nitrogen content

Activity Ip (mA/cm2)

Pt - 0.076

GC/ETek 20% Pt/C Naf - 1.3

GC/CNT-Pt PPP-Naf 0.0 12.4

GC/CNT-Pt PVP -Naf 6.63 16.2

GC/CNT-Pt PPY -Naf 10.5 21.4

GC/CNT-Pt PVI-Naf 16.7 18.6

Electrocatalytic activityElectrocatalytic activity

Electrocatalytic activity of the N-CNTs electrodes in comparison with commercial catalysts for methanol oxidation

Specific activity for methanol oxidation versus nitrogen content of the catalysts

Stability of the electrodesStability of the electrodes

Higher surface area of the CNT - better utilization of the catalytic particles

Tubular morphology & nitrogen presence - better dispersion of Pt

E-TEK < Pt PPP-CNT < Pt PVP-CNT < Pt PVI-CNT < Pt PPY-CNT

Nitrogen presence – dispersion & also in increasing the hydrophilic nature of the catalyst

Correlation between the catalytic activity and the nitrogen concentration (at%)

Salient FeaturesSalient Features

Electro-oxidation of methanol on PtElectro-oxidation of methanol on Pt/TiO/TiO22

nanotube catalystsnanotube catalysts

Pt with metal oxides Promoted mechanism(hydrogen spill over andoxygen spill over)

TiO2, WO3

Methanol oxidation catalystsMethanol oxidation catalystsMethanol oxidation catalystsMethanol oxidation catalysts

Pt alloys Intrinsic mechanism (bifunctional mechanism)

Pt-Ru

O

C

Pt

H

O

Ru

TiO2 Anatase /Alumina

Calcined at 873 K, 2 h

Alumina Membrane

Titanium isopropoxide in isopropanolImpregnation

3 M NaOH

Pt-TiO2 Nanotube

823 K, H2 atm, 3hImmersion in 73mM H2PtCl6, 12 h

Synthesis of Pt /TiOSynthesis of Pt /TiO22 nanotube catalyst nanotube catalyst

Raman spectrumUV Spectrum

UV and Raman spectraUV and Raman spectra

TiO2 nanotube Pt/TiO2 nanotube

SEM & SEM & TEM images TEM images of TiOof TiO22 nanotubes nanotubes

A - AnataseA - AnataseR - RutileR - RutilePt- PlatinumPt- Platinum

(111)(111)

X- Ray diffraction patternX- Ray diffraction pattern

ELECTRODE

10 mg Pt/TiO2 nanotubes/ 100 l water

Ultrasonicated for 30 min

Dispersion (10 l) / Glassy Carbon (0.07 cm2)

Dried in air

5 l Nafion (binder)

Solvent evaporated

• Counter electrode-platinum foil• Reference electrode-Ag/AgCl/KCl(saturated)

Electrode fabricationElectrode fabrication

Cyclic voltammograms in 0.5 M H2SO4 and 1 M CH3OH Scan rate : 50mV/s


Electrocatalyst

Anodic scan peak

potential (V) vs Ag/AgCl

Anodic peak current density

(mA cm-2)

Bulk Pt Bulk Pt 0.16

20 % Pt/C 0.762 1.3

Pt/TiO2

nanotube0.680 13.2

Model presentation of M-OH transfer and spillover upon metallic part of electrocatalyst.

Strong metal support interaction (SMSI) OH adsorption on TiO2 facilitates CO oxidation

Pt-CO + OH(ads) → Pt∙∙∙CO2 + H+ + e-

OH(ads) forms on TiO2 surface and oxidizes Pt-CO

T. Maiyalagan, B. Viswanathan and U. V. Varadaruju J. Nanosci. Nanotech 6 (2006) 2067

Promoting effect of TiOPromoting effect of TiO22 nanotubenanotube support support

TiO2 nanotubes have been explored as support for Pt

High platinum dispersion was obtained on these TiO2 nanotube supports by the reduction of the Pt ions with H2 at 873 K

The resulting electrodes were tested for methanol oxidation reaction and shows higher catalytic activity than the commercial catalyst

Strong metal support interaction (SMSI)

COads on the Pt sites reacts with surface hydroxyl species (OHads), at the adjacent TiO2 sites facilitates CO oxidation

TiO2 nanotube morphology was also assumed to be responsible for the higher specific activity of methanol oxidation


M.S. Antelman, Encyclopedia of chemical electrode potentials, Plenum, New York, 1982

Metal oxides - promising CO toleranceMetal oxides - promising CO tolerance

Pt + H2O PtO + 2 H+ + 2 e- Eo = 0.99V

Mo + 3H2O MoO3 +6 H+ + 6 e- Eo = 0.25V

W + 2H2O WO2 + 4H+ + 4 e- Eo = -0.05V

W + 3H2O WO3 + 6H+ + 6 e- Eo = 0.09V

Lower values of Eo for the Mo/MoOx, and W/WOx than that for Pt /PtO enhance the ability of OH adsorption Metal oxides forms hydrogen bronzes provides H2 spill over and oxygen spill over mechanism Ability to act as redox centers Ionic and Electronic conductivity

Metal oxides supports to Pt must fulfill the requirement of forming O-containing surface species at

low potentials

Electro-oxidation of methanol on Electro-oxidation of methanol on PtPt/WO/WO33 nanorods catalysts nanorods catalysts

P. K. Shen et al., Catalysis Today 38 (1997) 439

Electro-oxidation of methanol on Pt/WOElectro-oxidation of methanol on Pt/WO33 catalysts catalysts

10 gm Phosphotungstic acid + 30 ml methanol

WO3/Alumina membrane

WO3 nanorods(light blue powder)

H3PW12O40/Alumina membrane

Calcined at 873 K 3h

HF

ImpregnationImpregnation

Template Synthesis of WOTemplate Synthesis of WO33 nanorods nanorods

73 mM H2PtCl6

Evaporated to drynessH2 atm, 623 K, 4h

Pt/WO3 nanorods (dark powder)

500 1000 1500 2000 2500 3000

WO3 nanorods

Bulk WO3

HPW calcined

% T

ran

sm

itta

nce

Wave number (cm-1)

990 cm-1 is for as(W-Od)

1080 cm-1 is for as (X-Oa)

894 cm-1 is for as(W-Ob-W)

817 cm-1 is for as(W-Oc-W)

The strong absorption between 500 and 1000 cmThe strong absorption between 500 and 1000 cm-1-1 can be associated with the W-O-W can be associated with the W-O-W

stretching modes ( characteristic peak of tungsten oxide )stretching modes ( characteristic peak of tungsten oxide )

FTIR spectraFTIR spectra

UV spectrum

600 700 800 900

717.632

808.284 WO3 nanorods

In

tens

ity (a

.u)

Raman shift (cm-1)

717.6 and 808 cm717.6 and 808 cm-1-1 : O-W-O stretching modes : O-W-O stretching modes

Raman spectrum

UV and Raman spectrumUV and Raman spectrum

10 20 30 40 50 60 70 80

(001

)

(221

)

(220

)

(120

)

(011

)

Inte

nsi

ty (

a.u

.)

2 (degrees)

H3PW

12O

40

WO3 nanorods

XRD pattern of tungsten oxide nanorods


Mag:3000K

SEM/EDX imagesSEM/EDX images

0 500 1000 1500

0

200

400

600

800

1000

1200

W

WCu

CuPt

Pt

Cu

(b)

O

W

W

Co

un

ts

Energy (KeV)

200 nm 100 nm

TEM/EDX imagesTEM/EDX images

xH+ + xe- + WO3 ---------------> HxWO3

Bulk WO3 WO3 nanorods

(formation of hydrogen tungsten bronze)(formation of hydrogen tungsten bronze)


overlap between reoxidation of hydrogen tungstenoverlap between reoxidation of hydrogen tungsten bronze and desorption of hydrogen on Pt, difficult tobronze and desorption of hydrogen on Pt, difficult to estimate the active surface area of Ptestimate the active surface area of Pt

WO3 + xPt-H ---------- >HxWO3 + xPt-

H HxWO3 --------------->xH+ + xe- +

WO3

Pt + H+ + e- ---------- > xPt

Hydrogen spill-over effect on Pt/WOHydrogen spill-over effect on Pt/WO33 nanorods nanorods


Catalyst Pt loading g/cm2 Specific activity mA/cm2

Pt/Vulcan 20 23

Pt/WO3 nanorods

20 60

Metal oxide nanorods as supports for Pt electrodes in the electrooxidation of methanol in acid electrolyte has been investigated

WO3 was demonstrated to promote electrocatalytic oxidation of methanol by interacting with Pt via hydrogen spillover or through the formation of highly conductive tungsten bronzes

Improvement of performance may be due to the presence of OHads groups on the oxide surface, that should facilitate oxidation of poisoning CO intermediates

The promotional activity of WO3 nanorod is related to the W(VI)/W(IV) redox couple acting as a surface mediator for the oxidation of surface methanolic residues

The nanorods morphology of the base-metal oxide is promoting the activity for platinum


Why Conducting polymers ?Why Conducting polymers ? Easy Fabrication

Better stability

Good electronic /ionic conductivity

Three-dimensional structures and high porosity of the polymeric matrices leads to high dispersion

Minimum transport limitations

High dispersion of metallic particles inside these polymers gives electrodes with higher surface areas and enhanced electrocatalytic activity

Electro-oxidation of methanol on electrodeposited Electro-oxidation of methanol on electrodeposited platinum in platinum in

Poly(Poly(oo-phenylenediamine) nanotubule electrodes-phenylenediamine) nanotubule electrodes

Polyaniline,

Polypyrrole

Polythiophene

Poly (3,4, ethylenedioxythiophene)

Poly (2 hydroxy 3-amino phenazine)

Poly (o-aminophenol)

Poly (o-phenylenediamine) - high aromaticity and high thermal stability

- catalyst for electrochemical reduction of dioxygen

- sensor for many chemical species, ladder polymer

NH

HN

NH

HN *

*

n

Polymers matrices usedPolymers matrices used

Alumina membrane

Electrochemical

polymerization

Conducting composite

Matrix = Alumina membrane

Graphite electrode(Nafion coating)

Dissolution

Polymernanostructure

Nanotubes

0.6 µm-thickness 200 nm pore diameter

Template assisted electrochemical synthesis of Template assisted electrochemical synthesis of conducting polymer nanotubesconducting polymer nanotubes

Schematic view of an electrochemical cell for the formation of nanostructured materials. RE, reference electrode; AE, auxiliary electrode; WE, working electrode (template membrane with a deposited Nafion contact layer).

WE

RE

AE

Experimental setupExperimental setup

Graphite 1 cm2

Coating of 5 wt% Nafion,Al2O3 Membrane hot pressed on

Graphite at 393 K, 3 min.

Graphite /Naf/Al2O3

GR/Naf/Al2O3/PoPD

GR/Naf/PoPDtemp-Pt

Dissolution of Al2O3 in 0.2M NaOH, Followed

by immersion in 1% HBF4 (10 min)

0.5 M OPD / 0.5 M H2SO4

Scanned between -0.2 V to 1.2 V vs Ag/AgCl at 50 mV/s

GR/Naf/Al2O3-PoPD-Pt

Electro reduction in 0.01 M H2PtCl60.8 V to -0.2 V

Template assisted electrochemical synthesis of Template assisted electrochemical synthesis of Pt/PPt/PooPD nanotubulesPD nanotubules

Cyclic voltammograms during the electropolymerization of o-phenylenediamine in 0.5M oPD + 0.5M H2SO4 solution (v = 50mVs−1)

500 1000 1500 2000 2500 3000 3500

PoPD nanotubule

3112.982158.3

2493.9

1469.9

Inte

nsity

(a.u

)

Raman shift (cm-1)These bands are assigned to stretching of Aminobenzene units of azo groups

N-H stretching C=Stretching

812 cm−1 1,4-disubstitude ring

FT-IR and Raman spectrumFT-IR and Raman spectrum

200 400 600 800

transition

364.3

Wavelength (nm)

A

bso

rban

ce

PoPD nanotubule

UV spectrumUV spectrum

Graphite/PoPD nanotube AFMAFM

TEM image of Pt/PoPDGraphite/Pt-PoPD nanotube

Electron microscopic images of Pt/PoPD nanotubulesElectron microscopic images of Pt/PoPD nanotubules

Cyclic Voltammograms of GR/Naf/PoPD Temp in 0.5 M H2SO4 ( after the dissolution of the template)

-0.2 0.0 0.2 0.4 0.6 0.8 1.0

-80

-60

-40

-20

0

20

40

60

80

100

Cu

rren

t d

en

sit

y (

mA

/cm

2 )

(b) Nanotubule electrode (with methanol)

E/V vs Ag/Agcl

-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2-15

-10

-5

0

5

10

15

20

25

(c) Film electrode (with methanol)

Cu

rren

t d

en

sit

y (

mA

/cm2 )

E/V vs Ag/Agcl

-0.2 0.0 0.2 0.4 0.6 0.8 1.0-12

-10

-8

-6

-4

-2

0

2

4

6

8

10

C

urr

en

t d

en

sit

y (

mA

/cm2 )

(a) Nanotubule electrode (without methanol)

E/V vs Ag/Agcl


100 200 300 400 500 600

10

20

30

40

50

60

70

80

90

Film electrode

Tubule electrode

An

od

ic p

eak c

urr

en

t d

en

sit

y (m

A/c

m2 )

Pt Loading ( µg/cm2)

Plot of anodic peak current density as a function of Platinum loading on Nanotubule and conventional electrodes. (Current densities were evaluated from CV run in 0.5 M H2SO4 / 1M CH3OH at 50 mV/s )

S.No

Electrode Onset

Potential

(V)

Activity*

Forward sweep Reverse sweep

I( mA cm-

2)

E( mA cm-

2)

I( mA cm-

2)

E( mA cm-

2)

1

2

GR/Naf/PoPD Temp –Pt

GR/Naf/PoPD Conv –Pt

+0.1

+0.2

84

13.3a

0.82

0.70

--

6. a

---

0.45

* Activity evaluated from cyclic voltammogram run in 0.5 M H2SO4 / 1M CH3OH scanned between -0.2 and 1 V vs Ag/AgCl a peak current density (mA cm-2)


0

50

100

150

200

250

300

350

0 20 40 60 80 100 120

Time (min)

Cu

rre

nt

de

nsi

ty (

mA

/cm

2) GR/Naf/PoPD Temp –Pt

GR/Naf/PoPD Conv –Pt

GC/ 20 % Pt/C (E-TEK)

Stability of the electrodesStability of the electrodes

Template synthesis of conducting poly (o-phenylenediamine) yielded cylindrical nanotubules with outer diameter matches with pore diameter of the template used

Polymer nanotubules have adequate conductivity and allows both the incorporation of metal particles and an easy accessibility of the methanol to the catalytic sites.

Polymer nanotubules electrode have higher electrocatalytic activity than the conventional polymer film electrode.


Nanocomposites Organic-inorganic hybrid materials: “Compounds which contain both inorganic and organic moieties within the same micro structure”

Organic moiety - flexibility

Inorganic moiety - thermal stability and structural rigidity

Active moiety- catalysisNanocomposites with catalytic activity

• PPY-SiO2 and PANI-SiO2 hybrid nanocomposites offer large surface area - Exploited as host for entrapping large amount of metal particles with desirable catalytic activity

Electro-oxidation of methanol on Electro-oxidation of methanol on Pt supported Pt supported PEDOT/ VPEDOT/ V22OO55 nanocomposites nanocomposites electrodeselectrodes

Poly (3,4, ethylenedioxythiophene) (PEDOT)• Has wide potential range • Low band gap• Electroactive • Enhanced stability compared to polyaniline & polypyrrole• Excellent environmental stability • High electrical conductivity • Transparency in thin oxidized film • and is always in the p-doped state, i.e. conductive • Applications

– solid electrolytic capacitors,– antielectrostatic agents,– transparent electrodes in light emitting diodes, – and underlayers for the metallization of printed circuit boards

Vanadium(V) oxide xerogel (VXG)

Exhibiting high proton conductivity, as well as electronic conductivity arising from the presence of V(IV) ions

B. FolKesson et al., J. Electroanal. Chem., 267 (1989) 149

Comparison of the potentials at which methanol is usually oxidized electrochemically and the normal redox couples. The normal potentials of the probable intermediates in the methanol oxidation are also included

VOVO2+2+/V/V3+3+

VV3+3+/V/V2+2+

CHCH33OH/COOH/CO22HCHO/HCOOHHCHO/HCOOHCHCH33OH/HCHOOH/HCHO

HCOOH/COHCOOH/CO22

-0.5-0.5

EE00/V/V

00

+0.5+0.5

Van

adiu

m p

oten

tial

s an

d st

eps

of m

etha

nol o

xida

tion

Van

adiu

m p

oten

tial

s an

d st

eps

of m

etha

nol o

xida

tion

V2O5 catalysts for methanol oxidation

This PEDOT-V2O5 based organic inorganic nanocomposites could be a good Catalyst support for methanol oxidation

PEDOT is meant to substitute the carbon usually mixed with the inorganic oxide-based electrodes to improve their electronic conductivity; the PEDOT thus functions as electronic conductor

+13.4 A0

V2O5.nH2O gels

100 ml aqueous solution of hydrogen peroxide (10%)

0.75ml EDOT

Ammonium persulphate

PEDOT/V2O5 nanocomposite

Dried at 60 0 C

V2O5 Powder(1 g, or 5.5 10-3 mol)

Synthesis of poly(3,4-ethylenedioxythiophene)/ Synthesis of poly(3,4-ethylenedioxythiophene)/ VV22OO5 5 nanocomposites nanocomposites

PEDOT/V2O5 nanocomposite

20% Pt-PEDOT/V2O5nanocomposite

5 %H2Pt Cl6 (35ml) Stirring at 800C for 30 min to allow dispersion

CooledFiltered and washed with distilled waterDried in air oven at 125 C for 4h

0.1 N NaOH added to bring the pH 10-11

20% Formaldehyde

Stirred at 70C for 1 hour

Preparation of Pt /PEDOT/ VPreparation of Pt /PEDOT/ V22OO55 nanocomposite nanocomposite

FT-IR spectra of (a) V2O5 (b) V2O5 Xerogel and (C) PEDOT/V2 O5 nanocomposites

2000 1800 1600 1400 1200 1000 800 600 400

(V=O)

(V=O)

asym

(V-O-V)

asym

(V-O-V)(c)

(b)

(a)

(V=O)

asym

(V-O-V)

(a) V2O

5

(b) V2O

5 Xerogel

(c) PEDOT-V2O

5

Wavenumbers (cm-1)

% T

rans

mitt

ance

OH

After intercalation

Extra peaks --C-O-C stretching vibrations

FTIR spectraFTIR spectra

X-Ray diffraction patterns of (a) V2O5 and (b) PEDOT-V2O5 nanocomposite

5 10 15 20 25 30 35 40

d=1

3.4

d=3

.44

d=7

.01

(110

)

(002

)

(001

)

(310

)(0

11)(4

00)

(110

)

(101

)(0

01)

(200

)

(b)

(a)

(a) V2O

5

(b) PEDOT-V2O

5

Inte

nsi

ty

2 theta

After intercalationIncorporation of PEDOT in V2O5 increases the interlayer spacing to 13.4 A0


Thermogravimetric curves of (a) V2O5 (b) V2O5 xerogel and (c) PEDOT-V2O5 nanocomposite

first one step 8 % weight loss below 120 C----- due to water

second one step16.2 % weight loss up to 420 C ----combustion of organic polymer

mass gain 2.6 % up to 650 C ---- formation of orthorhombic V2O5

Thermal studiesThermal studies

SEM images of PEDOT/ VSEM images of PEDOT/ V22OO55 nanocomposite nanocomposite

Layered structure

SEM images of PEDOT/ VSEM images of PEDOT/ V22OO55 nanocomposite nanocomposite

SEM/EDX images of Pt-PEDOT/ VSEM/EDX images of Pt-PEDOT/ V22OO55 nanocomposite nanocomposite

EDX mapping of Pt on nanocomposite

Average particle size of 4.52 nm

XRD and TEM images of Pt-PEDOT/ VXRD and TEM images of Pt-PEDOT/ V22OO55

nanocompositenanocomposite

-0.2 0.0 0.2 0.4 0.6 0.8 1.0-0.10

-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04

VO2+/V3+

Cu

rrem

t (m

A)

Potential (mV)

PEDOT-V2O

5

V5+/VO2+

V5+

Cyclic voltammograms in 0.5 M H2SO4 Scan rate : 50mV/s


-200 0 200 400 600 800 1000 1200

-20

-10

0

10

20

30

20% Pt/C

20% Pt-PEDOT/V20

5

Potential (mV)

Cu

rren

t m

A/c

m2

Cyclic voltammograms in 0.5 M H2SO4 and 1 M CH3OH Scan rate : 50mV/s


Catalyst

Pt loadin

g g/cm

2

Methanol

oxidation

activity mA/cm2

Pt/(C6H4O2

S)0.4V2O5.0.5H2O10 28.4

Pt/Vulcan 10 15

Nearly two times higher activity for the same Pt loading

Methanol oxidation activity of Pt/ PEDOT-V2O5 catalyst prepared by formaldehyde reduction method

Electrocatalytic activity of the catalyst Electrocatalytic activity of the catalyst Stability of Stability of the electrodesthe electrodes

The Pt loaded on PEDOT-V2O5 nanocomposite has been evaluated as the electrode for methanol oxidation in acid medium

EDX mapping and TEM images shows fine dispersion of Pt particles in the nanocomposite leading to a better utilisation of the noble metal catalyst

Electrocatalytic activity of methanol oxidation reaction for Pt/PEDOT-V2O5 was higher than Pt/C


The salient points of the present investigation are:

The supports for noble metal electro-catalyst have a definite role in the development of electrodes for fuel cells

The functionalization of the support carbon materials is a mean to increase dispersion and also intrinsic activity of the noble metal sites

Oxide supports, though may lead to net loss of energy, can favour the removal of otherwise poisons for the noble metal electro-catalytic sites

Conducting polymers and their composites can be conceived as alternate supports for noble metal electrodes for effective dispersion and intrinsic activity

ConclusionsConclusions

Documents

Sep. 20, 2006 Ph.D., Seminar - II T. Maiyalagan CYD01006 Electro-catalytic supports for noble metals for exploitation as electrodes for fuel cells