Electrochemical Oxidative Desorption of Adsorbed Sulfur Species on (111) Surfaces of Single Crystals of Pure Pt and Pt-Based Bimetallic Alloys

The adsorption/desorption behavior of sulfur species at the (111) surfaces of pure Pt and various Pt-based bimetallic alloys, denoted as Pt3M (M = Co, Cu, Fe, Pd), was investigated by electrochemical measurements and X-ray photoelectron spectroscopy (XPS). After the adsorption of elemental sulfur, the current responses characteristic of the adsorption/desorption of hydrogen and hydroxyl species at the sulfur-free bare (111) surfaces completely disappeared, and a doublet peak corresponding to the elemental sulfur appeared in the S 2p region of XPS spectra. The characteristic current responses gradually recovered, simultaneously with the decrease of the S 2p peak, by repeating the potential cycling between -0.2 and 0.8 V vs Ag/AgCl, indicating the oxidative desorption of S species. Except for the Pt3Pd(111) surface, in which Pd has a similar atomic radius to Pt and fully occupied 4d orbitals, the Pt3M(111) surfaces showed higher oxidative desorption capability than those of the pure Pt(111) surface; electrochemically active surface area recovered at the Pt3M(111) surfaces by fewer potential cycles than at the Pt(111) surface. Among the various factors, the downshift of the d-band center due to the ligand effect of foreign metal and the electronic interaction between adsorbed S and Pt are the dominant factors promoting the oxidative desorption of sulfur as well as the strain effect of foreign metal with an atomic radius smaller than Pt.