Investigation of the positive electrode and bipolar plate degradation in vanadium redox flow batteries

This study investigates the degradation of the positive electrode and bipolar plate in vanadium redox flow batteries (VRFBs), focusing on the influence of state-of-charge (SoC) and temperature. CO 2 evolution was used as the indicator to assess the corrosion of SIGRACELL GFD 4.65 EA graphite felt electrode and four different carbon-polymer composite bipolar plates. These components were immersed in vanadium catholyte at varying SoCs and exposed to different temperatures. Our results reveal that the graphite felt corrosion increases exponentially with both SoC and temperature, with a carbon degradation rate estimated at ~0.5 wt% per year under typical VRFB operating conditions. The bipolar plates exhibited, in general, lower degradation, with temperature having a more pronounced effect than SoC. However, the findings highlight the importance of selecting the appropriate material, as corrosion resistance varied significantly between the different compositions tested. Additionally, CO 2 evolution was monitored during single-cell cycling tests under various conditions. All the different performed analyses suggest that VRFBs can operate safely up to 90 % SoC at temperatures below 35 °C without exceeding corrosion rates observed at the current operational thresholds of 80 % SoC and 40 °C. • Novel methodology to quantify corrosion in VRFBs. • Corrosion mapped for electrodes and BPPs across various SoCs and temperatures. • ~0.5% of the electrode felt corrodes annually in VRFBs. • Results suggest potential for extending the operational window of VRFBs. • Dynamic SoC limits based on temperature to protect stack health and boost capacity.