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
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