Boron-functionalized carbon felt electrode for enhancing the electrochemical performance of vanadium redox flow batteries

• The boron-doped carbon felt manufactured a facile thermal treatment with NH 4 BF 4 . • The nature of hydrophobic felt was transferred to super-hydrophilicity. • The boron-doped carbon felt enhanced electrochemical performances of VRFBs. Herein, boron-doped carbon felt (B-CF) was proposed as a promising electrode for ensuring the outstanding electrochemical performance of vanadium redox flow batteries (VRFBs). Boron-functional groups can be successfully introduced onto carbon felt (CF) via NH 4 BF 4 treatment. The hydrophobic nature of CF is changed to hydrophilicity via the incorporation of boron-functional groups, resulting in excellent affinity with the electrolytes of VRFBs. A VRFB cell containing B-CF exhibits higher energy efficiency (80.56%) than that of CF (63.40%) at 100 mA cm −2 current density. This improvement is attributed to the enhanced electrocatalytic properties of B-CF toward VO 2 + /VO 2+ and V 2+ /V 3+ redox reactions.