Modification Based on MoO 3 as Electrocatalysts for High Power Density Vanadium Redox Flow Batteries

Molybdenum oxide MoO 3 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, MoO 3 in the form of micro‐flakes was introduced onto carbon paper as an electrocatalyst and MoO 4 2− as electrolyte additive for the vanadium redox couple reactions in the vanadium redox flow battery (VRFB). When the carbon paper was modified with MoO 3 or MoO 4 2− added to the electrolyte, the peak potential separations were measured as 171 and 203 mV for V 2+ /V 3+ and 130 and 111 mV VO 2+ /VO 2 + redox reactions, respectively, as compared with 306 and 144 mV for the bare pre‐treated carbon paper. A vanadium redox flow cell with MoO 3 ‐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 MoO 3 ‐based modification is a promising method for high power density VRFB applications.