Mass transfer in micro-nano porous electrodes: A crucial role in optimizing vanadium redox flow battery performance

This study proposes a synergistic strategy combining resin coating with polyethylene glycol porogen etching. By simultaneously achieving structural reconstruction of the carbon matrix (targeted removal of redundant carbon) and a controlled thermal reduction process, a modified electrode with a micro-nano synergistic pore structure is successfully prepared. This electrode combines the structural advantages of low tortuosity and high mass transfer/diffusion coefficients. While maintaining high electrical conductivity, it significantly enhances mass transfer efficiency, effectively suppresses the hydrogen evolution side reaction, and thereby exhibits excellent electrochemical activity and enhanced reaction kinetics. The study further reveals the multi-dimensional regulation mechanism of the electrode pore structure, including the construction of mass transfer channels, optimization of the electrochemical interface, and synergy of reaction kinetics. It clarifies the synergistic enhancement mechanism of the "micro-pore spatial confinement effect" and the "nano-pore short-range diffusion advantage" in the hierarchical micro-nano structure, significantly improving the mass transfer performance of the electrode. The vanadium redox flow battery assembled with this electrode achieves an energy efficiency of 80.41 % at a current density of 200 mA·cm^-2 and demonstrates outstanding cycling stability, retaining 90 % of its initial efficiency after 1000 cycles, reflecting excellent long-term operational reliability. This work provides new insights for the development of flow battery electrodes with high power density and long cycle life.