MoO₃-Deposited Graphite Felt for High-Performance Vanadium Redox Flow Batteries

To overcome the challenge of the low power density of all-vanadium flow batteries, electrodes with enhanced electrochemical activity are necessary. A facile and scalable impregnation process was employed to deposit MoO3 particles on the surface of a graphite felt (GF) (MoGF) electrode. In the cyclic voltammetry profiles, the as-prepared electrode exhibits superior electrocatalytic activity toward the redox couple of VO2+/VO2+, significantly enhancing the reversibility, as indicated by the substantially reduced peak separation from 490 mV (pristine GF) to 245 mV (MoGF). The full-cell performance was also studied, where MoGF exhibited an extraordinary voltage efficiency (VE) of 71.42% at a high current density of 250 mA cm–2. The highest current density of most works is limited to ≤200 mA cm–2 with very few reporting the cell performance at 250 mA cm–2, which has generally achieved a VE of 66%. With regard to electrolyte utilization, the cell employing MoGF demonstrated a 139.69% improvement over the cell employing pristine GF at 150 mA cm–2. Furthermore, the cell employing GF underwent 50 charge–discharge cycles at 100 mA cm–2, delivering a stable VE of 87.1%. Physicochemical and electrochemical characterizations were carried out to unveil the catalytic effect of the deposited layer, which confirmed that not only orthorhombic MoO3 with high electrochemical activity and electrical conductivity was deposited but also a larger surface area and adequate oxygen functional groups were obtained through this facile fabrication process.