Core – Shell anodic catalysts for

Direct Methanoland

Direct Ethylene Glycol Fuel

Cells

Dima Kaplan 26.1.11

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OUTLINE

DMFC and DEGFC DMFC and DEGFC problems Why Core-Shell catalysts? Home made Core-Shell catalysts and their

performance Summary

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What is DMFC?

MeOH in

CO2 out

eHCOOHOHCH 66223 Anode reaction E˚a = 0.04 Volt vs. SHE

OHeHO 22 3665.1 Cathode reaction E˚c = 1.23 Volt vs. SHE

OHCOOOHCH 2223 25.1 Overall reaction E˚cell = E˚c – E˚a = 1.19 Volt

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What is DEGFC?

EG in

CO2 out

eHCOOHOHCH 101022 2222 Anode reaction E˚a = 0.01 Volt vs. SHE

OHeHO 22 510105.2 Cathode reaction E˚c = 1.23 Volt vs. SHE

OHCOOOHCH 22222 325.2 Overall reaction E˚cell = E˚c – E˚a = 1.22 Volt

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DMFC: current and possible applicationsCivilian applications

SFC EFOY – works like a mobile charger for the car’s battery.

Toshiba Dynario – Allows charging of Mobile Electronic Devices via a USB cable.

SFC Emily – recharges batteries that power the electrical devices on board the vehicle (radios, GPS, onboard computers) while the engine isn’t running.

SFC JENNY 600S – man portable FC, can power a number of electrical devices such as digital communications and navigation systems, computer and laser tracking devices, remote sensors, cameras and metering devices

Military applications

Catalysts for DAFC

• Currently, PtRu alloys are the most apropriate catalysts for DMFC.

• For operational temperature of 60°C – 80°C an alloy with atomic ratio of 1:1 was found to be most suitable for DMFC.

• Pt is responsible for MeOH and EG dehydrogenation, while Ru is responsible for H2O breakup, thus enabling the formation of CO2 at an acceptable potentials

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Problems preventing wide spread usage of DMFC

• Platinum is used as catalyst on both electrodes. Currently, fuel

cells use high Pt loadings, which leads to high catalyst cost.

• Nafion is used as the PEM. However, nafion is also expensive.

• Methanol crossover trough the PEM leads to reduction of

efficiency

• Long term durability is questionable due to:

– Anode catalyst poisoning by oxidation intermediates and loss of

structure integrity

– Cathode catalyst poisoning by methanol crossover, surface oxide

formation and loss of hydrophobic properties

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EG as potential fuel for DAFC

Pros:• Higher boiling point (1980C vs. 64.70C )• Lower toxicity than methanol• Greater volumetric capacity (4.8Ah/ml vs. 4.0Ah/ml) • Larger molecule, fuel crossover to the cathode can be much

lower Cons• Lower gravimetric capacity (4.32Ah/g vs. 5Ah/gr) • Complicated oxidation mechanism, high number of

intermediates• Current anode catalysts are optimized for methanol oxidation

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So what about the catalyst’s cost…..?

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Proposed solutionCore – Shell catalysts: Pt only in the shell

Because the catalysis occurs only on the surface of the electrode it’s logical to use Pt only in the shell of the nano-particals

Since exposed Ru sites are needed to break down H2O molecules, a partial monolayer of Pt on top of Ru core should be used

It’s likely, that the best surface PtRu composition for methanol oxidation will be atomic ~1-3:1 depending on the electro-oxidation mechanism EG oxidation might require a different surface composition

Ru corePtRu shell

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MA1 catalyst Pt on Ru on XC72

MA1 catalyst was prepared in a two stage synthesis:1. Electroless deposition of Ru on XC72, using EG as reducing agent2. Electroless deposition of Pt on Ru/XC72, using NaBH4 as reducing agent

Comparison to JM HiSPEC 7000: Pt:Ru (1:1) alloy catalyst with carbon support, 45% TM

MA1a catalyst - composition

MetalXPS results

Surface atomic ratio

EDS resultsWeight ratio

XRD particle size

Ru1555.4 nm for Ru2.7 nm for Pt Pt4.2845

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MA1 catalyst – MeOH oxidation activity Catalytic activity - MeOH oxidation

MetalECSAI0.45V

[m2/gr PtRu][A/gr Pt][A/gr PtRu][A/m2 PtRu]

MA1294712147.37

JM HiSPEC 7000

273462308.52

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MA1 catalyst – EG oxidation activity

Catalytic activity - EG oxidation

MetalECSAI0.45V

[m2/gr PtRu][A/gr Pt][A/gr PtRu][A/m2 PtRu]

MA1292411093.75

JM HiSPEC 7000

272631756.50

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DK6a catalystPt on Ru on XC72

DK6a catalyst was prepared in a two stage successive deposition synthesis:1. Electroless deposition of Ru on XC72, using NaBH4 as reducing agent2. Electroless deposition of Pt on Ru/XC72, using NaBH4 as reducing agent

DK6a catalyst - composition

MetalXPS results

Surface atomic ratio

EDS resultsWeight ratio

XRD particle size

Ru1801.3 nm

Pt0.4720

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DK4a catalystPtRu on IrNi on XC72

DK4a catalyst was prepared in a two stage successive deposition synthesis:1. Electroless deposition of IrNi on XC72, using NaBH4 as reducing agent2. Electroless deposition of PtRu on IrNi/XC72, using NaBH4 as reducing agent

DK4a catalyst - composition

MetalXPS results

Surface atomic ratio

EDS resultsWeight ratio

XRD particle size

Ru111

2 nm Pt0.3319

Ir0.2869

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MeOH oxidation activitysummary

CatalystSurface

composition (XPS)

Ma]amp/gr

Pt]

Ma]amp/gr

TM]

ECSA]m2/gr TM[

Sa]amp/m2

TM[

MA120%Pt/24%Ru/XC72

Ru:Pt1:4.28

471214297.37

DK6a15%Pt/59%Ru/XC72

Ru:Pt1:0.47

20441291.40

DK4a22%PtRu/54%IrNi/XC72

Ru:Pt:Ir1:0.33:028

920101254.04

JM HiSPEC 700045%PtRu/carbon

Ru:Pt 1:1.67

346230278.52

JM HiSPEC 1210075%PtRu/carbon

Ru:Pt 1:1.9

620416508.32

JM HiSPEC 12100: PtRu (1:1) alloy catalyst with carbon support, 75% TM

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EG oxidation activitysummary

Catalystsurface

composition (XPS)

Ma[amp/gr

Pt]

Ma]amp/gr

TM]

ECSA]m2/gr

TM]

Sa]amp/m2

TM]

MA120%Pt/24%Ru/XC72

Ru:Pt1:4.28

241109293.75

DK6a15%Pt/59%Ru/XC72

Ru:Pt1:0.47

526105293.62

DK4a22%PtRu/54%IrNi/XC72

Ru:Pt:Ir1:0.33:028

34137251.48

JM HiSPEC 700045%PtRu/carbon

Ru:Pt 1:1.67

263175276.50

JM HiSPEC 1210075%PtRu/carbon

Ru:Pt 1:1.9

316212504.24

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Summary

Several core – shell catalysts were synthesized. One of

them (DK4a) showed a superior performance in methanol

oxidation over commercial HiSPEC 12100 catalyst. The

other catalyst (DK6a) showed a superior performance in

EG oxidation over commercial HiSPEC 12100 catalyst.

Core shell catalysts have a potential to drastically reduce

the Pt loadings currently needed in DMFC and DEGFC.

Efforts to find a durable and cheaper (than Ru) core metal

should be made.

The results show that EG and methanol might require

different surface compositions of Pt:Ru.

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Acknowledgments

• Prof. Emanuel PeledProf. Emanuel Peled

• Dr. Larisa Burstein

• Dr. Yuri Rosenberg

• Dr. Jack Penciner

• All the electrochemistry group of TAU