The kinetics process of a Pb(ii)/Pb(0) couple and selective fabrication of Li–Pb alloys in LiCl–KCl melts

Abstract

The electrode reaction of Pb(II) and co-reduction of Li(I) and Pb(II) were investigated on a tungsten electrode in LiCl–KCl eutectic melts by a range of electrochemical techniques. From cyclic voltammetry and square wave voltammetry measurements, the reduction of Pb(II) was found to be a one-step diffusion-controlled reversible process with the exchange of 2 electrons. The diffusion coefficients of Pb(II) were computed, and they obey the Arrhenius law. Using the linear polarization technique, the kinetic parameters, such as exchange current intensity (j₀), standard rate constant (k⁰) and charge transfer resistance (R_ct) for the Pb(II)/Pb(0) couple on a tungsten electrode were studied at different temperatures, and the activation energy is 27.32 kJ mol⁻¹, smaller than the one for diffusion of Pb(II), which further confirmed that the reduction of Pb(II) was controlled by diffusion. A depolarisation effect for Li(I) reduction was observed from the results of cyclic voltammetry, square wave voltammetry and chronopotentiometry due to the formation of Li–Pb alloys by co-reduction of Li(I) and Pb(II). Furthermore, five Li–Pb intermetallic compounds, LiPb, Li₈Pb₃, Li₃Pb, Li₁₀Pb₃ and Li₁₇Pb₄ characterized by scanning electronic microscopy and X-ray diffraction, were selectively prepared by potentiostatic electrolysis on a tungsten electrode and galvanostatic electrolysis on a liquid Pb electrode, respectively.