The role of surface defects in CO oxidation, methanol oxidation, and oxygen reduction on Pt(111)

Some surface reactions of interest to electrocatalysis in alkaline media are promoted by crystalline defects, while others occur preferentially on defect-free terraces. Different forms of structure sensitivity, and the underlying causes of this structure sensitivity, have been examined using several fuel-cell-relevant surface reactions in alkaline media as model reactions. Oxidation of CO serves as a model for defect favored reactions, while reduction of oxygen serves as a model for terrace favored reactions. More complicated reactions, such as methanol oxidation, can be interpreted as containing multiple steps that are either defect favored or terrace favored. The role of defects in each of these reactions was interpreted in terms of geometric and electronic effects, with different types of defects (kink type and step type) showing different effects for the different electrocatalytic processes. CO oxidation is promoted by both step-type and kink-type defects, as a result of electronic structure, but methanol dehydrogenation is promoted only by step-type defects, as a result of geometric structure.