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

Abstract 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 V ³⁺ /V ²⁺ 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.