A comprehensive study of parasitic gas evolution reactions in a vanadium redox flow battery

Abstract

The gas evolution reactions (GERs) in a vanadium redox flow battery (VRFB) are dangerous and can cause a series of issues such as an imbalance in the state of charge (SOC) and electrode degradation, among others. To gain a deeper understanding of parasitic GERs in VRFBs, a transient multidimensional multiphysics VRFB model was developed by coupling the transport of multiphase species and electrochemical reactions. First, it was predicted that the hydrogen evolution reaction (HER) occurs during the whole charge-discharge process due to the negative activation overpotential of the HER whereas the oxygen evolution reaction (OER) occurs only at the end of the charging process. Second, the charging current has a strong effect on the HER in the region near the bipolar plate. Third, it was found that the HER increases almost seven times (from 163.3 A m−3 to 1167.1 A m−3) when the operating temperature increases from 298.15 K to 313.15 K. The temperature has a more significant effect on the activation overpotential of OER than that of HER. Furthermore, the increasing HER with the increasing SOC results in an SOC imbalance of 0.54% after 10 charge-discharge cycles, which accounts for 11% of the overall capacity loss.