Investigation on electrochemical behaviors of MnCl2 impurity in LiCl-KCl melts

Abstract

In this work, electrochemical behaviors of Mn(II) in LiCl-KCl melts were investigated at 723 K using cyclic voltammetry (CV), chronopotentiometry (CP) chronoamperometry (CA), and square wave voltammetry (SWV) techniques. Results from CV and SWV measurements show that the redox reaction of Mn(II) on a tungsten working electrode is a diffusion controlled quasi-reversible reaction with two electrons transferred, and the diffusion coefficient is determined as 1.01 × 10−5 cm2/s by using semi-integral method. The standard reaction rate constant of the order ≈ 10−3 cm s−1, determined by Nicholson method, placed the redox reaction of Mn in the quasi-reversible range per Matsuda-Ayabe criteria. CA results exhibit that the deposition of metal manganese on the tungsten cathode is an instantaneous nucleation process. Besides, the apparent standard potential of Mn(II)/Mn(0) couple and activity coefficient of Mn(II) are determined by EMF measurements. Additionally, the diffusion coefficients calculated by semi-integral method revealed that the temperature dependence obeyed the Arrhenius law. Finally, the exchange current density of Mn(II)/Mn(0) on tungsten electrode at various temperatures was analyzed by Tafel polarization technique.