Precision pore engineering of graphite felt via ultrafast non-equilibrium Joule heating for vanadium redox flow batteries

Vanadium redox flow batteries (VRFBs) are ideal candidates for grid-scale energy storage. However, commercial graphite felt (GF) electrodes suffer from inherent hydrophobicity, insufficient active sites, and sluggish mass transport, leading to severe electrochemical polarization and limited high-rate performance. Conventional methods are typically time-consuming and often cause irreversible structural damage to the bulk framework, accompanied by residual impurities. These drawbacks collectively impede their scalable application. Herein, an ultrafast non-equilibrium Joule heating strategy was developed. Utilizing the second-scale heating and cooling characteristics of this technique, oxidative etching was selectively confined to the surface layer of carbon fibers while the highly conductive bulk graphite framework was fully preserved, fabricating a heterostructure electrode with a unique “surface-disordered and bulk-ordered” architecture. The electrode fabricated under optimal conditions (900 °C/60 s) features a hierarchical micro-mesoporous network enriched with highly active C O groups. This architecture effectively resolves the intrinsic trade-off between active-site density and mass transport efficiency. The peak-to-peak separation of the vanadium redox reaction was reduced to 777.2 mV, and the apparent diffusion coefficient was increased by 2.3-fold. The assembled single cell delivers an energy efficiency of 78.8% at 200 mA cm⁻². Even under 300 mA cm⁻², the energy efficiency maintains at 71.5%. In 200 cycles, the capacity decay rate per cycle of the cell is very low, only 0.01%, and the peak power density is 516.5 mW cm⁻². This work provides a rapid, green, and scalable new route for the fabrication of high-performance carbon electrodes.