Electroreduction of S2O82- anions on chemically etched and electrochemically polished Bi(1 1 1) electrode

Electroreduction kinetics of S2O82- to SO42- anions at chemically etched (CHE) and electrochemically polished (EP) Bi(1 1 1) electrodes has been studied using rotating disc electrode method. The surface nanostructure of CHE Bi(1 1 1) and EP Bi(1 1 1) electrodes has been studied by in situ STM and the very different values of root mean squared roughness (Rms) have been obtained (∼1000 times higher for CHE Bi(1 1 1) (Rms ⩾ 143 nm) than for EP Bi(1 1 1) (Rms ⩾ 0.145 nm)). The influence of the nanoroughness of CHE Bi(1 1 1) on the current density, heterogeneous reaction rate constant and corrected Tafel plots (cTp) has been demonstrated. For CHE Bi(1 1 1) the more pronounced inhibition of electroreduction reaction at moderate negative surface charge density has been observed in comparison with EP Bi(1 1 1), caused by the differences in surface charge density and also in diffuse layer ψ0 potential drop values at crystallographically different homogeneous regions (planes) exposed at the surface of the macroheterogeneous polycrystalline CHE Bi(1 1 1) surface. The very low apparent transfer coefficient αapp obtained indicates the nearly activationless charge transfer mechanism for S2O82- electroreduction at the CHE Bi(1 1 1) electrode similarly to EP Bi(1 1 1). However, αapp only very weakly depends on Rms for the Bi electrodes at high negative surface charge densities where the values of ψ0 potential are nearly equal for different planes at fixed electrode potential. At very high negative surface charge densities the cationic catalysis through the adsorbed ion pairs Na+S2O82-) is possible.