Oxygen Reduction on Silver Low-Index Single-Crystal Surfaces in Alkaline Solution:  Rotating Ring DiskAg(hkl) Studies

The rotating ring disk method is applied to investigate the oxygen reduction reaction on Ag single-crystal surfaces in alkaline solution over the temperature range 293-333 K. At all temperatures, the oxygen reduction reaction proceeds through the 4e- reaction pathway with a very small (approximately 0.5-2%) peroxide formation. At the same temperature and overpotentials, the kinetics of the ORR always increases in the order (100) < or = (111) < (110), indicating that the reaction is structure-sensitive. We present an interpretation of the structure sensitivity based on the supposition that it arises from (i) a potential-dependent adsorption of spectator hydroxyl ions and (ii) variations in activation energies, which are determined by the O2 adsorption on Ag single-crystal surfaces covered by adsorbed oxygenated species.