High electrocatalytic activities of electrochemically exfoliated graphene-oxide deposited carbon paper electrodes for vanadium redox flow batteries

The effective and efficient preparation of highly electrocatalytic porous carbon electrodes is essential to enhance the competitiveness of vanadium redox flow batteries (VRFBs). In this work, electrochemically exfoliated graphene oxides (Exf–GOs) are prepared from graphite foil at large scale by a continuous Exf–GOs production system equipped with multi-electrodes and subsequent separation process. The Exf–GOs are deposited on the activated carbon paper (A−CP) substrate by a direct and simple infiltration–deposition approach. Collective electro-kinetics analysis applying cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) revealed that the resulting Exf–GO/A−CP electrodes exhibit two orders magnitude greater intrinsic electrocatalytic activities than the A−CP electrode for the VO2+/VO2+ redox reactions. A trade-off between the Exf–GO deposition amount and the open pore volume through the Exf–GO/A−CP electrodes exist that has critical impacts on the overall electro-kinetic performance of these composite electrodes. Compared to the A−CP electrode, the Exf–GO/A−CP electrode provided the VRFB with more than two-fold enhancements in the energy storage capacity, and at least (10–15) % higher the voltage and energy efficiencies. The results collectively demonstrate the high catalytic activities of the Exf–GO/A−CP composite electrodes for VRFBs prepared in the effective, highly scalable, and process-efficient approach.