Anode catalyses loadings

There is considerable interest in the use of non-noble metals for fuel-cell catalysis, which is not surprising when one considers the cost of the noble metal Pt (at well over 900 US per troy ounce) and its noble metal alloying additions. In a PEM fuel cell using pure hydrogen at the anode, Pt loading requirements down to 0.05 mg Pt cm" are manageable. On the other hand, the eathode eomponent of the MEA still requires a loading of 1 mg Pt em in the best ease seenario, due to the slow kinetics of the ORR. 

Improving bioanodes performances and efficiencies will be the most important task in future studies of enzymatic anodic catalysis. Based on research carried out in the past few years, trends for improving performance rely on better electron transport methods and higher enzyme loading. Electron transport could be improved, for example, by developing novel mediators and redox polymers for MET or by controlling orientation of enzymes to improve DET. Enzyme loading techniques could be improved to increase active enzyme concentration per unit of electrode area or volume. 

With respect to fuel cell catalysis, most research has been focused on cathode ORR catalysts development, because the ORR kinetics are much slower than flic anodic HOR kinetics in other words, the fuel cell voltage drop polarized by load is due mainly to the cathode ORR overpotential [7, 8]. However, in some cases the overpotential of the anodic HOR can also contribute a non-negligible portion of the overall fuel cell voltage drop [8]. Therefore, the catalytic HOR on the fuel cell anode catalyst is also worth examining. 

Figure 4.45. Cyclic voltammogram of 1 M formate (A) and lactate (B) on WC/graphite foil electrode at pH 5 in 0.1 M KCl at 293 K. Catalyst load 20 mg cm. The electrode potential is given vs. Ag/AgCl (SSCE.) Inset figures show the eurrent density measured at 0.2 V vs. SSCE as a function of anolyte concentration [217]. Dashed curve = blank electrolyte, solid curve = electrolyte with formate (A) or lactate (B). (Reproduced from Applied Catalysis B Environmental, 74(3-4), Rosenbaum M, Zhao F, Quaas M, WulffH, Schroder U, Scholz F, Evaluation of catalytic properties of tungsten carbide for the anode of microbial fuel cells, 261-9, 2007, with permission from Elsevier.)...

Figure 13.6. Durability of Pt/C and Pt Coi. /C-based MEAs tested iu a short stack (active area = 465 cm ) under H2-air at a ceU temperature of 80 °C and total reactant pressures of 150 kPUabs, with both anode and cathode humidities at 100% and anode and cathode reactant stoichiometries of s = 2/2. Data are shown with the stack under a constant load of 0.20 A/cm over 1000 h. Data were averaged over four cells of each type of MEA [1], (Reprinted from Applied Catalysis B Environmental, 56, Gasteiger HA, Kocha SS, Sompalh B, Wagner FT. Activity benchmarks and requirements for Pt, Pt-alloy, and non-Pt oxygen reduction catalysts for PEMFCs, 9-35, 2005, with permission from Elsevier.)...

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