Particle size and structural effects in platinum electrocatalysis

Of the several factors which influence electrocatalytic activity, particle size and structural effects are of crucial importance, but their effects and mechanism of interaction, vis-a-vis overall performance, have been, at best, vaguely understood. The situation is further aggravated by the use of a wide range of experimental conditions resulting in non-comparable data. This paper attempts systematically to present the developments to date in the understanding of these structural interactions and to point out areas for future investigation. The entire content of this review has been examined from the context of the highly dispersed Pt electrocatalyst, primarily because it has been examined in the greatest detail. In the first two sections a general idea on the correlations between surface microstructure and geometric model is presented. Subsequently, indicators of a direct correlation between particle size and catalyst support synergism are considered. The structural and particle size effect on electrocatalysis is examined from the point of view of anodic hydrogen oxidation and cathodic oxygen reduction reactions. The hydrogen and oxygen chemisorption effects, presented with the discussion on the anodic and cathodic electrocatalytic reactions, provide important clues toward resolving some of the controversial findings, especially on the dependence of particle size on the anodic hydrogen oxidation reaction. Finally, the effect of alloy formation on the cathodic oxygen reduction reaction is discussed, providing insights into the structural aspect.