Electrocatalysts intermetallic compounds

In alkaline electrolyzers, Ni is the only elemental cathode that can be used. It is generally considered as a fairly good electrocatalyst, but in facts it exhibits two shortcomings (i) its activity decreases with time [cf. the AVtterm in Equation (7.16)] especially under conditions of intermittent electrolysis and (ii) shutdown of industrial cells (for maintenance) leads to Ni dissolution at the cathode since this electrode is driven to more positive potentials by short-circuit with the anode. These shortcomings can be alleviated if Ni cathodes are activated, that is, if they are coated with a thin layer of more active and more stable materials. Activation has been attempted with a variety of materials from sulfides to oxides, from alloys to intermetallic compounds. 

For example, the addition of a small content of Au to Pd, e.g., a Pd9Auj alloy core achieves remarkable enhancement of the stability while retaining the ORR activity as high as that on PtMu/Pd/C [16]. MEA fuel-cell tests showed that PtML/Pd9Au/C remains active even after 200,000 potential cycles. In addition to alloys, highly stable, inexpensive intermetallic compounds can also be attractive candidates as the supports for PtMu- PtniL electrocatalyst with intermetallic Pd-Pb core exhibits an ORR activity superior to Pt/C [17]. 

The reduction of molecular oxygen that is supplied either directly from containers or in a diluted form as air constitutes the reaction at the cathode in fuel cells. The use of air is preferable for economic reasons. Platinum metals and alloys of platinum metals are electrocatalysts for acid and alkaline electrolytes. Silver, silver alloys, nickel, carbon, and intermetallic compounds represent less expensive electrocatalysts for the oxygen electrode in alkaline solutions. In contrast to the hydrogen electrode, the overvoltage of the oxygen electrode is large at temperatures below 100 °C when a reasonable current is drawn. 

Lux, K.W., Cairns, E.J. (2006) Lanthanide-platinum intermetallic compounds as anode electrocatalysts for direct ethanol PEM fuel cells I. Synthesis and characterization of Ln Pt 2 (Ln = Ce, Pr) nanopowders. Journal of the Electrochemical Society, 153, A1132-A1138. 

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