A study of the Ce(III)/Ce(IV) redox couple for redox flow battery application

In this study, the electrochemical behavior of the Ce(III)/Ce(IV) redox couple in sulfuric acid medium with various concentrations and the influence of the operating temperature were investigated. A change of the concentration of sulfuric acid mainly produced the following two results. (1) With an increase of the concentration of sulfuric acid the redox peak currents decreased. (2) The peak potential separation for the redox reactions increased with rising concentration of sulfuric acid from 0.1 to 2 M and then decreased with further increase of the concentration. Elevated temperature was electrochemically favorable for Ce(III)/Ce(IV) couple, which caused an increase of the peak currents for the redox reactions and a decrease of the peak potentials separation. Constant-current electrolysis shows that the current efficiency was 73% for the oxidation process of Ce(III) and 78% for the reduction process at 298 K, and could be improved by elevating the temperature. The open-circuit voltage of the Ce-V cell, after full charging, remained constant at 1.870±0.005 V for more than 48 h, and is about 29% higher than that of the all-vanadium batteries. The coulombic efficiency was approximately 87%, showing that self-discharge of the Ce-V battery was small. The preliminary exploration shows that the Ce(III)/Ce(IV) couple is electrochemically promising for redox flow battery (RFB) application.