The kinetics of electroreduction of europium(III) cations at bismuth single-crystal electrode

Electroreduction of Eu(ClO4)(3) and Eu-2(SO4)(3) has been studied at electrochemically polished Bi(01 (1) over bar) single-crystal electrode in an acidic HClO4 or H2SO4 (pH similar to 3) aqueous solution with LiClO4 or Na2SO4 additions as a surface inactive electrolyte. The Eu3+ cations electroreduction rate depends on the electrode potential applied and the concentration of the supporting electrolyte as well as the concentration of the Eu3+ ions. At the more negative electrode potentials than the zero charge potential (zcp), the diffusion current plateaus were observed. The values of the rate constant for the heterogeneous reaction calculated at zcp are independent of the base electrolyte concentration studied. Analysis of the kinetic data corrected for the electrical double-layer effect shows that the coincidence of the corrected Tafel plots can be achieved, assuming that the effective charge of a reactant (+1.6) is significantly lower than it would be expected (z(A)=+3).