OXYGEN REDUCTION ON PLATINUM LOW-INDEX SINGLE-CRYSTAL SURFACES IN ALKALINE-SOLUTION - ROTATING-RING DISK(PT(HKL)) STUDIES

The first results of a study of the oxygen reduction reaction on a rot ating ring-disk electrode using single-crystal Pt disk electrodes in a lkaline solution are presented. The order of activity of Pt(hkl) in 0. 1M KOH increased in the sequence (100) < (110) < (111) for both oxygen and peroxide reduction. These differences are attributed to the struc ture sensitivity of hydroxyl anion (OH.) adsorption on Pt(hkl) and its inhibiting (site blocking) effect on oxygen kinetics. Two different t ypes of OHads occur on Pt(100) and Pt(110), a reversible OHIV, and an irreversible OHir, while only the reversible form is formed on Pt(111) . Very small fluxes (I-R/N << 0.011(D)) of peroxide were detected at t he ring at potentials where the surfaces have only the reversible form of OHads. More peroxide (I-R/N < 0.03I(D)) was found with the Pt(100) and Pt(110)surfaces in the potential region where irreversible adsorp tion occurs. The mechanism of O-2 reduction was also affected by adsor bed hydrogen with increased formation of peroxide ions in this potenti al region; correspondingly, adsorbed hydrogen was found to have an inh ibiting effect on peroxide reduction, the effect decreasing in the ord er (111) > (100) >> (110).