EVALUATION OF RATE CONSTANTS AND REVERSIBILITY PARAMETERS FOR SURFACE-REACTIONS BY THE POTENTIAL-SWEEP METHOD

It is shown how the potentiodynamic sweep method, often used for qualitative evaluations of the behaviour of electrochemical processes, can provide a quantitative kinetic basis for evaluation of reversibility of electrochemical processes in a monolayer at an electrode surface. A characteristic quantity, s0, analogous to the exchange current density and related to the rate constant, k is defined. A method for evaluation of s0 for simple surface reactions involving chemisorbed species obeying two kinds of isotherms is proposed. Applications of the treatment are made to evaluation of s0 for two surface reactions of current interest: the adsorption of H and the formation of OH and O species on Pt, which were studied in aqueous HClO4, H2SO4 and KOH solutions. Problems which arise in the evaluation of s0, i0 and standard rate constants, k0, for a surface process involving multiple states of adsorption of the deposited species are discussed. It is shown that s0 is a useful parameter for characterizing the kinetics of electrode surface processes since, unlike i0, it does not depend on real area of the electrode. Hence, electrochemical characterization of suitable electrocatalyst surfaces can be made without recourse to real area determinations. © 1979 Elsevier Sequoia S.A.