Impedance spectroscopy of H and OH adsorption on stepped single-crystal platinum electrodes in alkaline and acidic media

The adsorption kinetics of hydrogen and hydroxyl on Pt(111) and stepped Pt[n(111) x (110)] electrodes with n = 29, 9, and 4 in acidic and alkaline electrolytes have been studied using impedance spectroscopy. We found a potential dependent charge transfer resistance, R-ct, (similar to 30 Omega cm(2) to similar to 1 k Omega cm(2)) for hydrogen underpotential deposition in alkaline media (0.05 M NaOH), whereas in acidic media (0.025 M HClO4) R-ct was too low to be determined accurately. Assuming simple (mean field) isotherms to fit our data, we obtain repulsive interactions between H-upd at the (111) terrace and effective attractive interactions at the steps. The adsorption of OH on (111) terraces is fast in both acidic and alkaline media.