A highly active biomass-derived electrode for all vanadium redox flow batteries

In this work, we report an environmentally friendly and low-cost approach to synthesize an all biomass-derived electrode from cotton through a pyrolysis process and apply this novel electrode to a VRFB for the first time. It is demonstrated that this carbonized cotton (CC) electrode presents a higher BET surface area, a larger number of oxygen-containing functional groups, a better wettability and higher catalytic activity for vanadium reactions than commercial carbon papers (CPs) do. As a result, the CC electrode improves the reversibility toward VO²⁺/VO₂⁺ by 100 mV lower peak separation as compared with commercial CPs. Moreover, the VRFB assembled with the prepared electrodes delivers a high voltage efficiency of 75.4% at a current density of 100 mA cm⁻², outperforming the oxidized CPs (68.3%), and a better rate performance during the charge-discharge test at various current densities. These results suggest that the carbonized cotton electrode offers a great promise for the large-scale application in VRFBs.