Direct electrocatalysts

Several activities, if successful, would strongly boost the prospects for fuel ceU technology. These include the development of (/) an active electrocatalyst for the direct electrochemical oxidation of methanol (2) improved electrocatalysts for oxygen reduction and (2) a more CO-tolerant electrocatalyst for hydrogen. A comprehensive assessment of the research needs for advancing fuel ceU technologies, conducted in the 1980s, is available (22). 

A viable electrocatalyst operating with minimal polarization for the direct electrochemical oxidation of methanol at low temperature would strongly enhance the competitive position of fuel ceU systems for transportation appHcations. Fuel ceUs that directiy oxidize CH OH would eliminate the need for an external reformer in fuel ceU systems resulting in a less complex, more lightweight system occupying less volume and having lower cost. Improvement in the performance of PFFCs for transportation appHcations, which operate close to ambient temperatures and utilize steam-reformed CH OH, would be a more CO-tolerant anode electrocatalyst. Such an electrocatalyst would reduce the need to pretreat the steam-reformed CH OH to lower the CO content in the anode fuel gas. Platinum—mthenium alloys show encouraging performance for the direct oxidation of methanol. 

A fuel cell is simply a device with two electrodes and an electrolyte for extracting power from the oxidation of a fuel without combustion, converting the power released directly into electricity. The fuel is usually hydrogen. The principle of a fuel cell was first demonstrated by Sir William Grove in London in 1839 with sulphuric acid and platinum gauze as an electrocatalyst, and thereafter there were very occasional attempts to develop the principle, not all of which were based on sound scientific principles , as one commentator put it. 

We have already referred to the Mo/Ru/S Chevrel phases and related catalysts which have long been under investigation for their oxygen reduction properties. Reeve et al. [19] evaluated the methanol tolerance, along with oxygen reduction activity, of a range of transition metal sulfide electrocatalysts, in a liquid-feed solid-polymer-electrolyte DMFC. The catalysts were prepared in high surface area by direct synthesis onto various surface-functionalized carbon blacks. The intrinsic... 

Predictive abihties regarding future promising directions in pursuit of more active ORR electrocatalysts ... 

Lee K, Savadogo O, Ishihara A, Mitsushima S, Kamiya N, Ota K-I. 2006. Methanol-tolerant oxygen reduction electrocatalysts based on Pd-3D transition metal alloys for direct methanol fuel cells. J Electrochem Soc 153 A20-A24. 

Mustain WE, Kepler K, Prakash J. 2007. CoPd, oxygen reduction electrocatalysts for polymer electrolyte membrane and direct methanol fuel cells. Electrochim Acta 52 2102-2108. Nagy Z, You H. 2002. Applications of surface X-ray scattering to electrochemistry problems. Electrochim Acta 47 3037-3055. 

Lamy C, Rousseau S, Belgsir EM, Coutanceau C, Leger JM. 2004. Recent progress in the direct ethanol fuel cell Development of new platinum-tin electrocatalysts. Electrochim Acta 49 3901-3908. 

Roth C, Martz N, Buhrmester T, Scherer J, Fuess H. 2002. In-situ XAFS fuel cell measurements of a carbon-supported Pt-Ru anode electrocatalyst in hydrogen and direct methanol operation. Phys Chem Chem Phys 4 3555-3557. 

Bianchini, C. and Shen, P.K. (2009) Palladium-based electrocatalysts for alcohol oxidation in half cells and in direct alcohol fuel cells. Chemical Reviews,... 

A] Qiu, J.-D., et al., Controllable deposition of platinum nanoparticles on graphene as an electrocatalyst for direct methanol fuel cells. The Journal of Physical Chemistry C, 2011. 115(31) p. 15639-15645. 

D. Chu, and R. Jiang, Novel electrocatalysts for direct methanol fuel cells. Solid State Ion. 148, 591-599 (2002). 

Q. Xin, Preparation of supported RRu/C electrocatalyst for direct methanol fuel cells, Electrochim. Acta 50, 2371-2376 (2005). 

Improvements in solid polymer electrolyte materials have extended the operating temperatures of direct methanol PEFCs from 60 C to almost 100 C. Electrocatalyst developments have focused on materials that have higher intrinsic activity. Researchers at the University of Newcastle upon Tyne have reported over 200 mA/cm at 0.3 V at 80 C with platinum/ruthenium electrodes having platinum loading of 3.0 mg/cm. The Jet Propulsion Laboratory in the U.S. has reported over 100 mA/cm at 0.4 V at 60 C with platinum loading of 0.5 mg/cm. Recent work at Johnson Matthey has clearly shown that platinum/ruthenium materials possess substantially higher intrinsic activity than platinum alone (45). 

Direct metal deposition from metallic sources has been extensively used for model catalyst deposition for high-throughput and combinatorial studies. However, these methods are also increasingly used to deposit practical electrocatalyst materials. The best known approach is the one developed by 3M researchers have used physical vapor deposition to deposit Pt and Ft alloys onto nanostructured (NS) films composed of perylene red whiskers. The approach has been recently been reviewed by Debe. ... 

Collins, J.A. 2001. Development of electrocatalyst materials for direct methanol fuel cells. Energy Marie Curie fellowship Conference, Profactor GmbH, Steyr, Austria, 16-19 May 2001. 

Investigations of enzyme-catalyzed direct electron transfer introduce the basis for a future generation of electrocatalysts based on enzyme mimics. This avenue could offer new methods of synthesis for nonprecious metal electrocatalysts, based on nano-structured (for example, sol—gel-derived) molecular imprints from a biological catalyst (enzyme) with pronounced and, in some cases, unique electrocatalytic properties. Computational approaches to the study of transition state stabilization by biocatalysts has led to the concept of theozymes . " ... 

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