Electroreduction of peroxodisulfate anion at a Cd(0001) single-crystal plane electrode

Abstract

Electroreduction of peroxodisulfate anion on electrochemically polished face Bi(111) in aqueous NaF solution with different additions of Na2S2O8 is studied by rotating-disc voltammetry. The S2O82- electroreduction rate depends on the electrode potential and base-electrolyte concentration, i.e. on the diffuse layer thickness. The kinetic current densities atE = const are obtained by the Koutecky-Levich method and used for the determination of the apparent rate constants of electroreduction of S2O82-. The charge number of the reacting S2O82- species is obtained; it depends on the surface-inactive electrolyte concentration and the electrode potential. The ψ0 potential values at the outer Helmholtz plane, obtained for various NaF + H2O systems according to Gouy-Chapman-Stern-Grahame (GCSG) model, are used for constructing corrected Tafel plots (CTP), which are linear atE- ψ0 < -0.9 V (SCE). The charge transfer coefficient oc for electrochemically polished Bi(111) somewhat decreases with the concentration of the base electrolyte (0.22 ≤α ≤0.27), but the value of α is practically independent of the S2O82- concentration in solution if cNaF = const. However, CTP noticeably depend oncNaF.