Phosphorus-doped carbon nitride as powerful electrocatalyst for high-power vanadium flow battery

Highlights: • Phosphorus-doped carbon nitride electrocatalysts are decorated on graphite felt (P-C₃N₄@GF). • P-C₃N₄@GF manifests improved electrolyte wettability and enhanced electrochemical activity. • P-C₃N₄@GF exhibits excellent rate performance at current density ranging from 50 to 300 mA cm⁻². • P-C₃N₄@GF demonstrates a maximum power density of 616.2 mW cm⁻². • The probable catalysis mechanisms of P-C₃N₄@GF towards positive/negative reactions are discussed. The poor hydrophilicity and weak activity of graphite felt (GF) electrodes hinder the efficient application of vanadium flow batteries (VFB). Therefore, enhancing the electrolyte wettability and electrochemical activity of GF is an effective way to improve the energy efficiency (EE) and power density of VFB. In this work, we report a simple and environmental friendly method to prepare phosphorus-doped carbon nitride modified GF (P-C₃N₄@GF) electrode, in which the P-C₃N₄ electrocatalysts are homogeneously distributed on the surface of GF. Owing to the excellent electrolyte wettability and notable electrocatalytic activity, the as-prepared P-C₃N₄@GF electrode exhibits significantly enhanced electrochemical activity towards VO²⁺/VO₂⁺ and V²⁺/V³⁺ redox couples. As a result, the VFB single cell with P-C₃N₄@GF electrode demonstrates outstanding rate performance at current densities of 50–300 mA cm⁻². Specifically, a maximum power density of 616.2 mW cm⁻² is achieved. Moreover, the P-C₃N₄@GF electrode exhibits superior stability and durability at a high current density of 150 mA cm⁻². Based on the above results, the possible catalysis mechanisms of P-C₃N₄@GF towards positive and negative reactions of VFB are discussed.