Electrode Kinetics of Oxygen Evolution and Dissolution on Rh, Ir, and Pt-Rh Alloy Electrodes

Abstract

Cathodic and anodic Tafel parameters, stoichiometric numbers, and decay kinetics have been determined on rhodium, iridium, and platinum‐rhodium alloy electrodes. Two regions of constant for a given substrate were observed. The catalytic activity of the substrates in acid solution above about 1.4v (vs. N.H.E.) was On the anodic side, the alloy substrate tends to behave as Rh, on the cathodic side as Pt. Time decay behavior was conventional except for the alloy surface, where the decay from the anodic side behavior resembled that on Pt. The stoichiometric number on Rh, Ir, and Pt‐Rh was about 2. Rate‐determining steps have been determined unambiguously by the criteria mentioned because of the existence and helpful diagnostic nature of two distinct values for on the anodic side, and because of the availability of stoichiometric numbers. After anodic polarization, Pt‐Rh electrodes behave as if the substrate were an individual area of Pt and Rh oxides. A model which rationalizes this deduction is suggested.