Investigation on electrochemical behaviors of Ni(II) impurity in LiCl-KCl melt

Abstract

This work concerned the electrochemical behaviors of Ni(II) in LiCl-KCl melt at the temperature of 673 K. The methods of Cyclic voltammetry (CV), square wave voltammetry (SWV) and open circuit chronopotentiometry (OCP) were used during the investigation. The semi-integral curve derived from CV measurements showed that the reduction of Ni(II) was a quasi-reversible process. And the standard reaction rate constant of the order ≈ 10−3 cm s−1, determined by Nicholson method, placed the redox reaction of Ni in the quasi-reversible range per Matsuda-Ayabe criteria. The apparent standard potential and activity coefficient of Ni(II) were studied by EMF measurements. According to the standard apparent potentials at different temperatures, the values of enthalpy and entropy changes were −269.293 kJ mol−1 and 0.0965 kJ mol−1 K−1, respectively. CA results showed that deposition of metal Ni on the tungsten cathode was an instantaneous nucleation process. Additionally, the diffusion coefficients calculated by semi-integral technique showed that the temperature dependence was consistent with Arrhenius’ law. And the activation energy for diffusion of Ni(II) is 57.87 kJ mol−1. Finally, the exchange current density of Ni on tungsten electrode was explored by linear polarization method.