Rotating-disc electrodes. ECE and DISP1 processes

Abstract

Theory is presented for the shape of current–voltage curves measured at a rotating-disc electrode for the cases where the substrate reacts via either an ECE or a DISP 1 process in which the kinetic step is sufficiently fast to allow the use of the reaction-layer concept in the theoretical treatment. When the electrode potential for the electrode reaction can be found under conditions where there are no complications of coupled kinetics, analysis of the shift in half-wave potential with disc rotation speed allows the deduction of the rate constant for the kinetics of the homogeneous chemical process involved in each mechanism. If an independent measurement of this rate constant is available (e.g. from spectroelectrochemistry) then discrimination between ECE and DISP1 pathways is possible. Experiments involving the reduction of fluorescein in aqueous carbonate/bicarbonate buffers were found to be in good agreement with theory. Furthermore, comparison of the kinetic data with transient electrochemical e.s.r. data revealed the reaction mechanism to be DISP1, in agreement with previous observations.