Study of the impedance of a platinum electrode in the system Br2/Br (HClO4, aq.)—II. Mechanism of the electrode reaction

The Randles circuit well represents impedance measurements carried out with activated Pt electrodes. This enables us to study the variation of j_o for redox reactions with concentration of the reactants, at constant potential, and also the variation of j_o with potential, keeping constant the concentration of one of the reactants. The results thus obtained indicate that the step Br₂ + e Br₂⁻ is rate-determining; it is followed or preceded by the rapid equilibria Br₂⁻ Br⁻ + Br 2Br Br₂. The mechanisms proposed hitherto for the electrochemical behaviour of the halogen/halide systems at inert electrodes are discussed, and it is reasoned that the ‘reversibility’ of these systems increases in the order Cl₂/Cl⁻ < Br₂/Br⁻ < I₂/I.