Pt single crystal surfaces in electrochemistry and electrocatalysis

In this review, recent advances in the use of platinum single-crystal surfaces in electrochemistry are addressed. The starting point is the voltammetric characterization in a supporting electrolyte because the profile can be used as a fingerprint of the surface, allowing the surface quality and solution cleanliness to be established. The signals appearing in these voltammograms have been assigned to the adsorption of H, OH, and the anions in the supporting electrolyte. Then, the distinctive behavior of the Pt(111) electrode regarding the adsorption of species and the electrocatalysis in comparison with the other single-crystal surfaces is discussed. For the H/OH adsorption, the (111) ordered domain is the only one in which both processes appear in different potential windows. For the remaining ordered domains, steps, and kinks, both processes overlap, giving rise to signals that correspond to the competitive adsorption/desorption of OH and H. This fact implies that OH may be adsorbed on the surface at potentials as low as 0.15 V, which is a paradigm shift in the up-to-now prevailing understanding of the electrochemical behavior of platinum electrodes and has important implications for the elucidation of the mechanism of electrocatalytic reactions. The effects of this new knowledge on the proposed reaction mechanisms for the oxidation of CO and small organic molecules and the reduction of oxygen and hydrogen peroxide are discussed in detail. Since the elucidation of the reaction mechanisms requires in many cases the use of computational modeling, the conditions that the models should fulfill to reach valid conclusions are discussed. Relevant examples, which highlight the importance of the local structure of the interphase in the electrochemical behavior are given.