Structural effects in electrocatalysis

Abstract

Studies of chemical reactions on well-defined surfaces provide fundamental data on surface reactivity and guidelines for the understanding and design of catalytic materials but few such studies have been done in electrocatalysis. We report here a study of the oxidation kinetics of HCOOH, CH3OH and CH2O on single crystal platinum electrodes with (100), (110) and (111) orientations. Pronounced dependence of the kinetics of these reactions on the crystallographic orientation of the surface has been found. The potential regions where reactions take place, the peaks of voltammetry curves, and the magnitude of currents at the peaks are different for each plane. These differences are explained on the basis of adsorption of a strongly bound intermediate, which shows a pronounced dependence on the symmetry of the single crystal planes. This intermediate completely blocks the Pt (100) surface; the smallest adsorption is at the (111) plane. On activation, the (100) surface shows the highest activity. These results suggest that electrocatalytic reactions exhibit structural sensitivity. They also provide guidelines for designing catalysts for the oxidation of small organic molecules to be used in electrochemical energy conversion.