Modification Based on MoO3 as Electrocatalysts for High Power Density Vanadium Redox Flow Batteries

Abstract Molybdenum oxide MoO3 has been widely used in catalysts and electrochemical energy devices, but, to date, has not been investigated as an electrocatalyst in redox flow cells. In this study, MoO3 in the form of micro‐flakes was introduced onto carbon paper as an electrocatalyst and MoO42− as electrolyte additive for the vanadium redox couple reactions in the vanadium redox flow battery (VRFB). When the carbon paper was modified with MoO3 or MoO42− added to the electrolyte, the peak potential separations were measured as 171 and 203 mV for V2+/V3+ and 130 and 111 mV VO2+/VO2+ redox reactions, respectively, as compared with 306 and 144 mV for the bare pre‐treated carbon paper. A vanadium redox flow cell with MoO3‐CP electrodes exhibited a voltage efficiency of 85.4 % at 100 mA cm−2. The power density reached 200 mW cm−2 at a current density of 150 mA cm−2 when cycled within the voltage range of 0.6–1.7 V. These results indicate that MoO3‐based modification is a promising method for high power density VRFB applications.