Influence of the Second Coordination Sphere on the Electrochemical Behavior of Chromium Complexes in Chloride Melts: Experimental and Calculation Methods

The cyclic voltammetry method was used to determine the standard rate constants of charge transfer (k(s)) on a glassy carbon electrode for the Cr(III)/Cr(II) redox couple in the systems of NaCl-KCl-CrCl3, KCl-CrCl3, and CsCl-CrCl3 in the temperature range of 973-1173 K. It was shown that k(s) increase with increasing temperature and decreases as sodium cations are replaced by potassium and cesium cations in the second coordination sphere of chromium complexes. The calculations carried out using the Firefly quantum-chemical software by means of the DFT method showed that the values of the charge transfer activation energy change monotonously in the series of Na-K-Cs in accordance with the ratio of reorganization energies. In its turn, this leads to monotonous variation of the charge transfer rate constants.