Bimetallic Catalysts for the Electro-oxidation of Hydrocarbon ......new catalysts and understanding...

Florida Universities Hydrogen Review 2005Florida Solar Energy Center November 1-4, 2005

Bimetallic Catalysts for the Electro-oxidation of Hydrocarbon Fuels – McElwee-White – University of Florida

Bimetallic Catalysts for the Electro-oxidation of Hydrocarbon Fuels

Lisa McElwee-WhiteUniversity of Florida

Start Date = 1 January 2004Planned Completion = 31 December 2007



Research Goals and Objectives

Objective: Synthesize heterobimetallic complexes and evaluate them as catalysts for methanol electrooxidation as a model for direct utilization of hydrocarbons in fuel cells

Crucial Questions:• Can the function of bulk Pt/Ru alloy be reproduced in a

simple complex using much less precious metal?• Can simple complexes immobilized on anodes serve as

electrocatalysts for fuel cells?• Can cheaper, more readily available, more active first row

transition metals be used in catalysts?



Relevance to Current State-of-the-Art

• For direct utilization of hydrocarbon fuels in fuel cells, state of the art is DMFC with Pt/Ru surface serving as anode catalyst

Relevance to NASA

• Future direct use of hydrocarbon fuels in fuel cells will require new catalysts and understanding of the reactions involved



Budget, Schedule and DeliverablesBudget • $ 40,000 for the grant period 10/1/05 to 3/31/07

Deliverables• 1st Quarter: oxidation data from previously prepared Fe/Pt, Fe/Pd and

Fe/Au catalysts and comparison to Ru/Pt, Ru/Pd, Ru/Au analogues

• 2nd Quarter: modified carbon paste electrodes with neutral catalysts• 3rd Quarter: bulk electrolysis data from modified carbon paste

electrodes• 4th Quarter: new Ru/Pt, Ru/Pd, Ru/Au, Fe/Pt, Fe/Pd and Fe/Au

catalysts with charged ligands• 5th Quarter: modified Nafion electrodes with charged catalysts• 6th Quarter: bulk electrolysis data from modified Nafion electrodes



Anticipated Technology End Use

• Results on single molecule catalysts and use of more active first row transition metals could be generally relevant to direct utilization of hydrocarbons in fuel cells



Accomplishments and ResultsMethanol as a model for more complex hydrocarbon fuels

– Complex oxidation mechanism

– Requires activation of C-H bonds

CH3OH - 2 e-

CH2O + 2 H+

CH2O- 2 e- CO + 2 H+

HCOOH - 2 e-

CO2 + 2 H+

CO + H2O - 2 e-

CO2 + 2 H+

CH2O + H2O- 2 e- HCOOH + 2 H+

CH2O + 2 CH3OH CH2(OCH3)2 + H2O

HCOOH + CH3OH HCO2CH3 + H2O



Accomplishments and ResultsSynthesis of Charged Catalysts for Modified Electrodes

Ru I

PPh2Ph2PPh3P

NHMe2I-

RuI

PPh2Ph2PPh3P

NHMe2I-

Pd

Cl

Cl

RuI

PPh2Ph2PPh3P

NHMe2I-

Pt

Cl

Cl

Pd(COD)Cl2

Pt(COD)Cl2

• Positive charge facilitates incorporation into Nafion for preparation of modified electrodes



Accomplishments and ResultsSynthesis of First and Second Row Metal Catalysts for Comparison

FeI

Ph2POC

PPh2

FeI

OCOC Pt

I

I

Pt(COD)I2Fe

I

Ph2POC

PPh2

RuI

Ph2POC

PPh2

RuI

OCOC Pt

I

I

Pt(COD)I2Ru

I

Ph2POC

PPh2

dppm

dppm

• Catalytic behavior of 1st row metal (Fe) can be compared to 2nd row (Ru)



Accomplishments and ResultsRu and Fe heterobimetallic complexes

RuI

Ph2POC

PPh2

Pt

I

I

RuI

Ph2POC

PPh2

Pd

I

I

FeI

Ph2POC

PPh2

Pt

I

I

FeI

Ph2POC

PPh2

Pd

I

I

RuI

Ph2POC

PPh2

Au

I

FeI

Ph2POC

PPh2

Au

I

FeI

Ph2POC

PPh2

RuI

Ph2POC

PPh2

υco= 1958 cm-1

υco= 1947 cm-1

υco= 1980 cm-1

υco= 1992 cm-1

υco= 1939 cm-1

υco= 1949 cm-1

υco= 1972 cm-1

υco= 1984 cm-1



Accomplishments and Results

Cyclic Voltammetry

RuI

Ph2POC

PPh2

Pt

I

I

E vs. NHE (V)

0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4

I (µA

)

-100

0

100

200

300

400

500

600

5 mM catalyst50 µL MeOH5 µL H2O 1.160 V

1.962 V1.843 V

RuI

Ph2POC

PPh2

Pd

I

I

E vs. NHE (V)

0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4

I (µA

)

-50

0

50

100

150

200

250

300

350

5 mM catalyst50 µL MeOH5 µL H2O

1.134 V

1.582 V

2.036 V

1.432 V

FeI

Ph2POC

PPh2

Pd

I

I

Pd(II/IV)Fe(II/III)

Fe(III/IV)

Ru(II/III)

Ru(III/IV)

Pd(II/IV)



Charge (C)

0 20 40 60 80 100 120 140

Pro

duct

evo

lutio

n (µ

mol

)0

10

20

30

40

DMM from Ru/Pd DMM from Ru/Pd-PPh3

Charge (C)

0 20 40 60 80 100 120 140

Pro

duct

evo

lutio

n (µ

mol

)

0

20

40

60

80

100

DMM from Ru/PtMF from Ru/PtDMM from (Ru/Pt + PPh3)MF from (Ru/Pt + PPh3)

Accomplishments and ResultsBulk Electrolysis: Product Evolution for Electrooxidation of Methanol by

Ru/Pt and Ru/Pd Heterobimetallic Complexes

RuI

Ph2POC

PPh2

Pt

I

IRu

I

Ph2POC

PPh2

Pd

I

I

DMM = CH2(OCH3)22 e- oxidation

MF = HCO2CH34 e- oxidation



Charge (C)

0 20 40 60 80 100 120 140

Pro

duct

evo

lutio

n (µ

mol

)

0

10

20

30

40

DMM from Ru/Pd DMM from Ru/Pd-PPh3

Accomplishments and ResultsBulk Electrolysis: Product Evolution for Electrooxidation of Methanol by

Ru/Pd and Fe/Pd Heterobimetallic Complexes

Charge (C)

0 20 40 60 80 100 120

Pro

duct

evo

lutio

n (µ

mol

)

20

30

40

50

60

70

80

DMM from Fe/PdDMM from Fe/Pd-PPh3

RuI

Ph2POC

PPh2

Pd

I

I

DMM = CH2(OCH3)22 e- oxidation

MF = HCO2CH34 e- oxidation

FeI

Ph2POC

PPh2

Pd

I

I



Accomplishments and ResultsSummary

• Heterobimetallic Ru/Pt, Ru/Pd, Ru/Au, Fe/Pt, Fe/Pd and Fe/Au complexes have been synthesized

• Cationic Ru/Pt and Ru/Pd complexes have been prepared for incorporation into Nafion films for fabrication of modified electrodes

• These heterobimetallic complexes have been demonstrated to be catalysts for the electrochemical oxidation of methanol

• Fe/Pt and Fe/Pd binuclear complexes are more active catalysts than their Ru/Pt and Ru/Pd analogues



Future Plans

• Fabricate carbon paste electrodes modified with neutral catalysts

• Fabricate modified electrodes using Nafion films impregnated with cationic catalysts

• Test modified electrodes for electrooxidation of methanol

• Continue synthesis of catalysts bearing first row metals– additional Fe/Pt, Fe/Pd, Ru/Ni, Fe/Ni complexes designed

• Evaluate performance of new catalysts for electrooxidation of methanol as a model for hydrocarbon systems

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Bimetallic Catalysts for the Electro-oxidation of Hydrocarbon ......new catalysts and understanding...

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