Effect of electrode porosity on the charge transfer in vanadium redox flow battery

Vanadium redox flow battery (VRB) has attracted enormous attention as a large-scale energy storage system owing to its long life, stable capacity and high safety. The electrode porosity plays a crucial role in the performance of VRB. This work reports the effect of electrode porosity on the electrocatalytic activity and charge transfer in VRB using spent tea derived porous carbon as electrode material. The electrode porous microstructure is systematically modified and specific surface area is enhanced from ~10 to ~2085 m² g⁻¹, with microporosity up to ~1930 m² g⁻¹. The electrochemical performance of modified electrodes is comprehensively investigated by cyclic voltammetry, impedance spectroscopy and galvanostatic charge/discharge studies. The modified electrode with high degree of porosity improves the charge transfer process and exhibits lower charge transfer resistance with higher electrocatalytic activity for vanadium redox reactions. Moreover, the VRB static cell performance demonstrates superior energy, voltage and coulombic efficiencies for modified electrodes than the pristine graphite electrode at all tested current densities. The results suggest that the tailored porosity substantially influences the charge migration and significantly improves the VRB performance.