Potential-induced surface restructuring--the need for structural characterization in electrocatalysis research.

The necessity of the careful structural characterization of model electrodes before and after the electrochemical measurements for a proper mechanistic interpretation is demonstrated for a well-known electrocatalytic system, bulk CO oxidation on PtRu model electrodes. Bimetallic, Pt-monolayer-island-modified Ru(0001) electrodes, which were prepared and characterized by scanning tunneling microscopy under ultrahigh-vacuum conditions, were found to undergo a distinct restructuring when they were potential cycled to 1.05 VRHE , while up to 0.90 VRHE they are stable. The restructuring, which is not evident in base voltammograms, is accompanied by a significant increase in the CO oxidation activity at low potentials (0.5-0.8 V), indicating that it is caused by new active sites created by the restructuring, and not by the PtRu sites that existed in the original surface and that were previously held responsible for the high activity of these bimetallic surfaces in terms of a bifunctional mechanism.