Fuel cell anode materials

This is the most common test method employed to qualify the leak characteristics of a new seal material. The test method involves applying the seal between two ceramic discs or between a ceramic and a metal disc, pressurizing the cavity formed by the seal and monitoring the pressure decay as a function of time.22 Alternatively, a metal tube and a ceramic disc can also be used [34], Typically, the cavity is pressurized to about 2 psi and the leak rate is determined by the pressure decay as a function of time. These tests can be done at room temperature or elevated temperatures. Similar test arrangement has also been used to test a plastically deformable brazed metal seal between fuel cell anode material and Haynes 214 washer [35], The cavity is pressurized to measure the rupture strength of the seal material. 

Liu Y, Lowe MA, DiSalvo FJ, Abruna HD (2010) Kinetic stabilization of ordered intermetallic phases as fuel cell anode materials. J Phys Chem C 114 14929-14938... 

Tao SW, Irvine JTS (2004) Catalytic properties of the perovskite oxide Lao.75Sro.25Cro.5Feo.503 in relation to its potential as a solid oxide fuel cell anode material. Chem Mater 16 4116-4121... 

Poisoning of platinum fuel cell catalysts by CO is undoubtedly one of the most severe problems in fuel cell anode catalysis. As shown in Fig. 6.1, CO is a strongly bonded intermediate in methanol (and ethanol) oxidation. It is also a side product in the reformation of hydrocarbons to hydrogen and carbon dioxide, and as such blocks platinum sites for hydrogen oxidation. Not surprisingly, CO electrooxidation is one of the most intensively smdied electrocatalytic reactions, and there is a continued search for CO-tolerant anode materials that are able to either bind CO weakly but still oxidize hydrogen, or that oxidize CO at significantly reduced overpotential. 

The Pt/Ru catalyst is the material of choice for the direct methanol fuel cell (DMFC) (and hydrogen reformate) fuel cell anodes, and its catalytic function needs to be completely understood. In the hrst approximation, as is now widely acknowledged, methanol decomposes on Pt sites of the Pt/Ru surface, producing chemisorbed CO that is transferred via surface motions to the active Pt/Ru sites to become oxidized to CO2... 

Tao, S. and Irvine, J. T. S. A Redox-Stable Efficient Anode for Solid-oxide Fuel Cells, Nature Materials, 2, 320 (2003). 

Gorte R J etal, 2000, Anodes for Direct Oxidation of Dry Hydrocarbons in a Solid Oxide Fuel Cell. Advanced Materials, doi.wiley.com. 

Strasser, P. et al.. High throughput experimental and theoretical predictive screening of materials a comparative study of search strategies for new fuel cell anode catalysts, J. Phys. Chem. B, 107, 11013, 2003. 

The high-cost of materials and efficiency limitations that chemical fuel cells currently have is a topic of primaiy concern. For a fuel cell to be effective, strong acidic or alkaline solutions, high temperatures and pressures are needed. Most fuel cells use platinum as catalyst, which is expensive, limited in availability, and easily poisoned by carbon monoxide (CO), a by-product of many hydrogen production reactions in the fuel cell anode chamber. In proton exchange membrane (PEM) fuel cells, the type of fuel used dictates the appropriate type of catalyst needed. Within this context, tolerance to CO is an important issue. It has been shown that the PEM fuel cell performance drops significantly with a CO con-... 

Porous metallic structures have been used for electrocatalysis (Chen and Lasia, 1991 Kallenberg et al., 2007). Porous electrodes are made with conductive materials that can degrade under high temperatures at high anodic potential conditions. This last problem is of less importance for fuel cell anodes, which operate at relatively low potentials, but it can be of importance for electrochemical reactors. Porous column electrodes prepared by packing a conductive material (carbon fiber, metal shot) forming a bar are frequently used. Continuous-flow column electrolytic procedures can provide high efficiencies for electrosynthesis or removal of pollutants in industrial situations. Theoretical analysis for the electrodeposition of metals on porous solids has been provided by Masliy et al. (2008). 

Finally, it should be noted that numerous perovskite-related materials with relatively low oxygen ionic conductivity at 700-1200 K have been excluded from consideration in this brief survey, but may have potential electrochemical applications in fuel cell anodes, current collectors, sensors, and catalytic reactors. Further information on these applications is available elsewhere 1-4, 11, 159, 217-219]. 

Wilson, J. R. et al. Three-dimensional reconstruction of a solid-oxide fuel-cell anode. Nature Materials 5, 541-544, doi 10.1038/nmatl668 (2006). 

J. R. Wilson, W. Kobsiriphat, R. Mendoza, H. Y. Chen, J. M. Hiller, D. J. Miller, K. Thornton, P. W. Voorhees, S. B. Adler, and S. A. Barnett. Three-dimensional reconstruction of a solid-oxide fuel-cell anode. Nature materials 5, (2006) 541-544. 

S. Tao and J. T. Irvine. A redox-stable efficient anode for solid-oxide fuel cells. Nature materials 2, (2003) 320-323. 

Platinum has been the most widely used catalyst, since it (and its alloys) is the only sufficiently efficient catalyst material for oxygen reduction in low temperature (< 120 °C) fuel cells. For fuel cell anodes, Pt-Ru alloys provide better tolerance to CO in the fuel stream (hydrogen from reformed methane or methanol) and have been found to be most effective for methanol oxidation. 

In conventional fuel cell designs, the electrolyte not only mediates the electrochemical reactions taking place at the anode and cathode, but also separates the fuel from the oxidant to prevent direct combustion. It was already recognized by Gool [235] that (i) many fuels do not directly react with oxygen at typical fuel cell temperatures and (ii) the catalytic activity of anode and cathode materials are quite selective to certain type of reactions. This renders possible single chamber fuel cells, that is, fuel cells without separation of anode and cathode compartment (sometimes called mixed gas fuel cells). Anode and cathode may then be placed either on the two sides of the electrolyte like in... 

By considering Eqs. 3.1 and 3.2, three clear requirements for SOFC anode materials can be derived. First, oxygen anion cOTiductivity is required to transport the reactant oxygen anions to the reaction site. Secmid, the anode must selectively facilitate the desired electrocatalytic oxidatimi of the fuel. Third, facile electrical conductivity is required to transport the product electrons from the reaction site to the current collector wire. These material requirements are in additirm to considerations of materials compatibility and stability during cell fabricatirm and operation, porosity in the electrode for fuel and product gas-phase diffusion, structural integrity, tolerance to impurities in the fuel and anode materials, and redox stability in case of accidental oxidation. 

Since the discovery of carbon nanotubes in the early 1990s [273] there has been emerging interest in their applicability as catalyst supports for low-temperature PEMFCs. Recently, Lee et al. reviewed the area of Pt electrocatalyst preparation techniques using carbon nanotubes and nanofibers as supports [274]. Here, the emphasis will be on the impact of novel nanostructured carbon supports (ordered mesoporous materials, nanotubes, and nanofibers) on the electrocatalytic activity with respect to direct fuel cell anodes. 

Chen J, Sarma LS, Chen C, Cheng M, Shih S, Wang G, et al. Multi-scale dispersion in fuel cell anode catalysts Role of Ti02 towards achieving nanostructured materials. J Power Sources 2006 159 29-33. 

There are clear differences between chemical and microbial fuel cell anodes. The most obvious difference is that anodes of MFCs must be able to support the growth of biological organisms. MFC anodes must also be highly conductive in order to efficiently collect electrons produced by bacteria as small increases in material resistance can have a significant impact on maximum power outputs. Other considerations when selecting an anode material include the expense of the material and the ability for it to be manufactured on a large scale. 

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