The kinetics of electroreduction of peroxodisulfate ions on single crystal cadmium and bismuth electrodes

The electroreduction of the peroxodisulfate anions on the electrochemically polished (EP) Cd(0 0 0 1), Bi(1 1 1) and Bi ( 0 1 1 ¯ ) planes has been studied by cyclic voltammetry, rotating disc electrode and impedance methods. The rate constant values of the heterogeneous electroreduction reaction of the S 2 O 8 2 - anion on the EP Cd(0 0 0 1) and Bi(h k l) planes dependent on electrode polarisation and base electrolyte concentration have been calculated. The values of apparent transfer coefficient αapp corrected for the double layer effect (αapp ⩽ 0.15) only very weakly depend on the electrode potential and base electrolyte concentration. The very low values of the apparent charge transfer coefficient for S 2 O 8 2 - electroreduction show that the activationless charge transfer mechanism is valid for EP Cd(0 0 0 1) and EP Bi(h k l) electrodes in various surface inactive base electrolyte solutions. This conclusion is in a good agreement with the theoretical models for the high hydrogen overvoltage metals based on the diabatic charge transfer mechanism from the metal to an ion [R.R. Nazmutdinov, D.V. Gluhov, O.A. Petrii, G.A. Tsirlina, G.N. Botikova, J. Electroanal. Chem. 552 (2003) 261].