In Situ Preparation of Bismuth Nanoparticles Encapsulated in Porous Carbon Spheres on Graphite Felt Electrodes for Vanadium Redox Flow Batteries

Vanadium redox flow batteries (VRFBs) attract significant interest for large-scale energy storage. However, the inherently low catalytic activity and restricted specific surface area of the pristine graphite felt electrodes hinder the further development of VRFBs. Herein, a facile in situ synthesis is reported of Bi nanoparticles encapsulated in N-doped carbon spheres on graphite felt (Bi@NC/GF). The resulting multicore-shell nanostructure exhibits enhanced electrocatalytic activity toward the V³⁺/V²⁺ redox couple, attributed to the synergistic effect between dispersed Bi cores and N-doped carbon matrix. Density functional theory analysis further verifies that the electronic structure at the core-shell interface significantly enhances vanadium-ion adsorption. Meanwhile, the porous carbon shell not only facilitates electron transfer but also enlarges the electrolyte-accessible surface area, thereby promoting electrolyte penetration. As a result, the battery employing Bi@NC/GF achieves an energy efficiency of 79.22% at 300 mA cm^-2 and a peak power density of 1254.32 mW cm^-2. Furthermore, the battery demonstrates outstanding cycling stability, with minimal performance decay over 1000 cycles. This work offers a promising strategy for advancing composite electrode design for next-generation VRFBs.