Functional nano-carbon layer decorated carbon felt electrode for vanadium redox flow batteries

Vanadium redox flow batteries (VRFBs) hold significant promise for large-scale energy storage applications. However, the sluggish reaction kinetics on the electrode surface considerably limit their performance. Implementation of efficient surface modification on carbon electrodes through an economically viable production method is crucial for the practical application of VRFBs. Herein, a nano-carbon layer with morphology of fine nanoparticles (<90 nm) and rich oxygen functional groups was constructed on carbon felts by unbalanced magnetron sputtering coupled with thermal treatment. This modified carbon felt served as both anode and cathode in cell, enabling an improved wettability of electrolyte and high reversibility of the active mass, and promoted kinetics of redox reactions. The optimized carbon felt, achieved through one hour of deposition (1C-CF), demonstrated outstanding electrochemical performance in a single cell. The cell exhibited a high energy efficiency of 82.4% at a current density of 100 mA cm⁻² and maintained 71.8% at a high current density of 250 mA cm⁻². Furthermore, the energy efficiency remained at 77.2% during long-term cycling (450 cycles) at a current density of 150 mA cm⁻², indicating good electrode stability. Our results shed light on the surface design of carbon felt electrodes for the broad application interest of VRFB energy storage systems.