Catalysts materials, anode

Operating pressure 1.2 bar Catalyst material formation 3oTi7oOx Si02 suspension + impregnation finally anodic oxidation... 

Fuel cell technology continues to advance with materials research. The catalyst material has been one of the major expenses in fuel cell design. An anode with about 40% less catalyst has been developed at Forsc-hungszentrum Julich GmbH in Julich, Germany. It has a bipolar plate with areas of different catalytic activity levels. The anode substrate has one phase that does not act as catalyst to methane-vapor reforming reactions, and another phase where it acts as a catalyst. 

The structure of a SPE cell is shown in Fig. 2.3. The basic unit of a SPE electrolyzer is an electrode membrane electrode (EME) structure that consists of the polymer membrane coated on either side with layers (typically several microns thick) of suitable catalyst materials acting as electrodes [43,49,50], with an electrolyzer module consisting of several such cells connected in series. The polymer membrane is highly acidic and hence acid resistant materials must be used in the structure fabrication noble metals like Pt, Ir, Rh, Ru or their oxides or alloys are generally used as electrode materials. Generally Pt and other noble metal alloys are used as cathodes, and Ir, Ir02, Rh, Pt, Rh-Pt, Pt-Ru etc. are used as anodes [43,46]. The EME is pressed from either side by porous, gas permeable plates that provide support to the EME and ensure... 

Rasten, E., Hagen, G., and Tunold, R., Anode catalyst materials for PEM-electrolysis, in New Materials for Electrochemical Systems IV. Extended Abstracts of the Fourth International Symposium on New Materials for Electrochemical Systems, Montreal, Quebec, Canada, July 9-13, 2001, pp. 278-280. 

The anode and cathode electrodes currently consist of Pt or Pt alloys on a carbon support. Two low-cost, nonprecious metal alternative materials for anode catalysts are WC and WO. Pt alloyed with W, Sn, or Mo has also been evaluated for anode catalyst materials. Some non-Pt cathode catalysts that are being evaluated include TaOo.92> Nj osZrO, pyrolyzed metal porphyrins such as Ee- or Co-NJC and... 

Since Pt dissolution is favored by high electrode potential, relative humidity, and temperature, the possibility to limit the risk of electrocatalyst aging is based on the use of Pt-alloy catalyst instead of pure platinum, at least for the cathode, which is characterized by higher potential with respect to anode, and by adoption of operative conditions not too severe in terms of humidity and temperature. While this last point requires interventions on the membrane structure, the study of catalyst materials has evidenced that a minor tendency to sintering can be obtained by the addition of non-noble metals, such as Ni, Cr, or Co, to the Pt cathode catalyst [59, 60], suggesting a possible pathway for future work. On the other hand also the potential application of non-platinum catalysts is under study, in particular transition metal complexes with structures based on porphyrines and related derivatives have been proposed to substitute noble metals [61], but their activity performance is still far from those of Pt-based catalysts. 

Investigate alternative catalyst materials for use in reconfigured anodes. 

Conventional potassium hydroxide electrolytic cells are made from carbon steel. Areas with high corrosion potential are frequently clad with nickel, plastic, or ceramic material. The cathode is constructed of steel coated with a catalyst. The anodes and cathodes of bipolar cells are usually made from nickel or nickel-coated steel. Diaphragms were originally made from asbestos reinforced with nickel nets. Because of the health hazards associated with the use of asbestos, ceramics and polymers are being considered as substitute materials. 

Currently used electrode-catalysts (anode and cathode) consist of an assembly of metallic nanoparticles usually deposited on an electronic conducting substrate and embedded in a hydrated membrane [10, 11], which is the polymer electrolyte proton-conductive material (Figure 17.1). What differs between cathode and anode is the catalyst material, and also the significantly slow kinetics of the cathode oxygen reduction reaction compared to that of the anode hydrogen oxidation reaction. For this reason, several... 

Studies of the clean and Pt-modified carburized W single crystals provided a fundamental understanding of how methanol decomposition proceeds under UHV conditions. These studies suggest that tungsten carbide-based electrocatalysts, especially metal-modified tungsten carbides, are promising anode catalyst materials to replace Pt in the DMFC. These conclusions are further examined on more applicable polycrystalUne foils. These foils are better representations of the complex morphology... 

Considering the high cost and the limited availability of platinum, the development of Pt-free fuel cells is necessary. Very recently, tests were carried out on Pt-free ADAFCs [134-139], in particular on cells with Pd-based catalysts as anode materials and ethanol as the fuel, being Pd the best catalyst for ethanol oxidation. These ADAFCs presented high performance, and particularly, Bianchini et al. [ 134] reported exceptionally high values of power density (55 mW cm at 20 °C and 170 mW cm at 80 °C) for the ADEFC formed by a Tokuyama A-006 anion-exchange membrane, Pd-(Ni-Zn)/C as anode catalyst and Fe-Co as cathode... 

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. 

The best catalyst material for both anode and cathode PEM fuel cell is platinum. Since the catalytic activity occurs on the surface of the platinum particles, it is desirable to maximize the surface area of the platinum particles. A common procedure for surface maximization is to deposit the platinum particles on larger carbon black particles [21]. 

Platinum has been considered to be the best catalyst for both the anode and the cathode though there is a large difference between the ORR and the hydrogen oxidation reaction (HOR) using the same catalyst. A great deal of effort has been made by many researchers toward developing appropriate catalyst materials, especially for the ORR, and platinum is so far still the best option. Therefore, in many PEMFCs, the anode and the cathodes use an identical catalyst platinum. 

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