A critical review on the recent progress of vanadium redox flow battery materials for electrolytes, membranes and electrodes preparation

The transition to renewable energy sources necessitates efficient energy storage solutions, driving research into redox flow batteries (RFBs). This review examines recent advancements in improving vanadium-based RFBs, focusing primarily on the electrolytes, electrodes, and membrane modifications. Innovations in electrolytes such as incorporating nanofluids, ionic liquids, and additives, significantly enhanced the overall electrochemical characteristics of the battery. Nanofluids like reduced graphene oxide (rGO) and carbon nanotubes (CNTs) improved the electrode kinetics and energy density, while ionic liquids enhanced the solubility of vanadium salts. In addition to these, additives such as sodium phosphate and chloride ions enhanced the capacity retention of VRFBs and redox couples' reactivity. Additionally, the membrane modifications were primarily aimed to enhance the ion selectivity and resistance to vanadium ion transport, thereby reducing the self-discharge of the battery. A variety of novel membranes prepared by the incorporation of polymers or ionic liquids showcased a significant improvement in ion selectivity and battery performance compared to conventional Nafion membranes which are explored in detail. These modifications to the existing redox flow battery technology offer a promising alternative to the traditional ones, paving the path for improved performance and widespread adoption of RFB's technology in large-scale grid-based energy storage solutions.