Electrochemical Performance of VO2+/VO2+Redox Couple in the H2SO4-CH3SO3H Solutions

The mixed acids with different ratio of H2SO4 to CH3SO3H were prepared, and their application in the vanadium redox flow battery (VRFB) as supporting electrolytes had been examined. It was found the solubility and stability of vanadium ions can be significantly enhanced by the increasing of CH3SO3H content in the mixed acid system. The electrochemical behaviors of VO2+/VO2+ couple in different mixed acids were further studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results showed that the electrochemical activities, including the reversibility of electrode reaction, the reaction resistance for VO2+/VO2+ couple were closely related to the CH3SO3H content in the mixed acid system, and reached the best value in the solution using 2.75 mol/L H2SO4+0.25 mol/L CH3SO3H mixed acid as supporting electrolyte. The VRFB with the optimized mixed acid electrolyte exhibits higher energy efficiency and the similar current efficiency compared with those of H2SO4 system.