Carbon and metal-based catalysts for vanadium redox flow batteries: a perspective and review of recent progress

As one of the most promising electrochemical energy storage systems, vanadium redox flow batteries (VRFBs) have received increasing attention owing to their attractive features for large-scale storage applications. However, their high production cost and relatively low energy efficiency still limit their feasibility. One of the critical components of VRFBs that can significantly influence the effectiveness and final cost is the electrode. Therefore, the development of an ideal electrocatalyst with low cost, high electrical conductivity, large active surface area, good chemical stability, and excellent electrochemical reaction activity toward the VO2+/VO2+ and V2+/V3+ redox reactions is essential for the design of VRFBs. Extensive research has been carried out on electrode modification routes for VRFBs to improve the energy density and overall performance for large-scale applications. This review article focuses on numerous state-of-the-art modification methods for VRFB electrodes, including those based on carbon materials, metal and metal oxide-based materials, and metal oxide/carbon composite materials. The challenges in the development of electrode materials and future research directions are also proposed.