Investigation of interfacial reaction kinetics of I −(aq) with Ag 2O(s) on Ag substrate: Determining mass transport and surface reaction rates

Abstract

The reaction kinetics of AgI formation by reaction of Ag 2O films with aqueous iodide were followed by monitoring the open-circuit potential ( E OC). Previous studies have shown that complete conversion of Ag 2O to AgI is indicated by an abrupt transition in the E OC from a value close to the equilibrium potential for the Ag|Ag 2O|H 2O system to one close to that for Ag|AgI|I −, allowing an easy determination of the total reaction time, τ f . The solid–solution interfacial kinetic parameters can then be determined by measuring τ f as a function of the initial amount of Ag 2O and the I − concentration. In this study, the application of the technique was extended to examine the effect of I −(aq) transport to an Ag 2O surface by measuring τ f as a function of electrode rotation rate. By studying the chemical conversion as a function of electrode rotation rate we are able to separate mass transport effects from the reaction kinetics. The interfacial reaction follows kinetics typical of a sequential binary-reaction system consisting of mass transport to, followed by reaction at, the surface. The mass transport rate was proportional to the square root of the electrode rotation rate, consistent with the well-established diffusion-boundary layer model for a rotating disc. Varying the rotation rate allows a quantitative extrapolation of the data to the infinite rotation rate to determine the chemical reaction rate at the surface.