Surface oxidation and reduction of platinum electrodes: Coverage, kinetic and hysteresis studies

Studies on the electrochemical formation and reduction of surface oxide at platinum electrodes have been carried out with particular reference to polarization and hysteresis effects in these processes. Comparisons between the results of galvanostatic and potential sweep techniques have been made for three types of surfaces of platinum electrodes prepared by: (a) heating in hydrogen; (b) heating in a flame; and (c) electrolytically forming platinum black surfaces. The dependence of the quantity of reducible oxide formed under prior steady-state potentiostatic conditions has been related to potential and time of anodic polarization. Polarization effects in the reduction of the surface oxide have been evaluated in terms of the potential dependence of the pseudocapacitance maximum for the oxide reduction process, and a mechanism for the reduction is suggested. The relative slowness of the reduction process is important in regard to the question of the role of oxide in the kinetics of electrocatalytic oxidations at platinum anodes. Hysteresis effects in anodic formation and cathodic reduction of the oxide are discussed in terms of a totally irreversible phase transition involving the ad-layer.