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Core – Shell anodic catalysts for Direct Methanol and Direct Ethylene Glycol Fuel Cells

Core – Shell anodic catalysts for Direct Methanol and Direct Ethylene Glycol Fuel Cells. Dima Kaplan. 26.1.11. OUTLINE. DMFC and DEGFC DMFC and DEGFC problems Why Core-Shell catalysts? Home made Core-Shell catalysts and their performance Summary. MeOH in. CO 2 out. Anode reaction.

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Core – Shell anodic catalysts for Direct Methanol and Direct Ethylene Glycol Fuel Cells

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  1. Core – Shell anodic catalysts for Direct MethanolandDirect Ethylene Glycol Fuel Cells Dima Kaplan 26.1.11

  2. OUTLINE • DMFC and DEGFC • DMFC and DEGFCproblems • Why Core-Shell catalysts? • Home made Core-Shell catalysts and their performance • Summary

  3. MeOH in CO2 out Anode reaction E˚a = 0.04 Volt vs. SHE Cathode reaction E˚c = 1.23 Volt vs. SHE E˚cell = E˚c – E˚a = 1.19 Volt Overall reaction What is DMFC?

  4. EG in CO2 out Anode reaction E˚a = 0.01 Volt vs. SHE Cathode reaction E˚c = 1.23 Volt vs. SHE E˚cell = E˚c – E˚a = 1.22 Volt Overall reaction What is DEGFC?

  5. DMFC: current and possible applications Civilian 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. Military applications 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

  6. 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 EGdehydrogenation, while Ru is responsible for H2O breakup, thus enabling the formation of CO2 at an acceptable potentials

  7. 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

  8. 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

  9. So what about the catalyst’s cost…..?

  10. Proposed solution Core – 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 core PtRu shell

  11. MA1 catalyst Pt on Ru on XC72 • MA1 catalyst was prepared in a two stage synthesis: • Electroless deposition of Ru on XC72, using EG as reducing agent • Electroless deposition of Pt on Ru/XC72, using NaBH4 as reducing agent ComparisontoJM HiSPEC 7000: Pt:Ru (1:1) alloy catalyst with carbon support, 45% TM

  12. MA1 catalyst – MeOH oxidation activity

  13. MA1 catalyst – EG oxidation activity

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

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

  16. MeOH oxidation activitysummary JM HiSPEC 12100: PtRu (1:1) alloy catalyst with carbon support, 75% TM

  17. EG oxidation activitysummary

  18. 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.

  19. Acknowledgments • Prof. Emanuel Peled • Dr. Larisa Burstein • Dr. Yuri Rosenberg • Dr. Jack Penciner • All the electrochemistry group of TAU Ahead of the pack with a fuel cell stack!!

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