Complementary Actions of Tungsten Oxides and Carbon to Catalyze the Redox Reaction of VO2+/VO2+ in Vanadium Redox Flow Batteries

Abstract Redox flow batteries (RFBs), which are based on the redox reaction of vanadium ions, are expected to be a promising energy buffer for renewable energy because of their large‐scale potential. However, the reaction overvoltage associated with the redox of vanadium ions is large, and highly active electrocatalysts are urgently needed. In this study, we prepared thin‐film model electrodes to evaluate the catalytic activities of tungsten oxide, which is known to be an electrocatalyst for accelerating the redox of vanadium ions and investigated the reaction mechanism. The results showed that tungsten oxide only catalyzed the reduction of VO 2 + , while carbon only catalyzed the oxidation of VO 2+ , but not both redox reactions. Our results revealed for the first time that the catalytic sites active in the charging and discharging of RFB are different, which is an important finding for the construction of highly active electrocatalysts.