Identification of the Reduction Reaction Mechanism of V3+ on a Graphite Electrode in Acidic Solutions

The oxidation and reduction reaction mechanisms of the VO2 +/VO2+ redox couple have been studied to better understand the electrode reaction processes and further optimize the battery performance of vanadium flow battery (VFB) in our previous work. However, it is found that the negative electrode process of VFB plays a more important role in the improvement of the overall battery performance as research continues. Hence, the reduction reaction mechanism of V3+ in acidic solutions has been investigated systematacially in this work. Potentiodynamic polarization combined with rotating disk electrode have been applied to calculate the reaction orders (m) and the electron transfer number (n) of the reduction reaction of V3+. The results of this work demonstrated that the reduction reaction of V3+ is a single electron transfer step and H+ keeps out of the electrochemical reaction. Furthermore, the kinetic equation for the reduction reaction of V3+ has been established, and the theoretic polarization curve based on the established kinetic equation is well consistent with the experimental result, indicating an accurate prediction of the polarization behavior in V3+ acidic solutions.