Oxygen‐Vacancy‐Engineered CoSnO ₃ /rGO Nanocubes as High‐Performance Cathode Electrocatalysts for Advanced Vanadium Redox Flow Batteries

Oxygen vacancy‐engineered CoSnO ₃ /reduced graphene oxide (CoSnO ₃ /rGO) serves as a durable cathode electrocatalyst for vanadium redox flow batteries (VRFBs). Structural and spectroscopic analyses confirm the formation of defect‐rich amorphous CoSnO ₃ uniformly integrated with a conductive rGO network, which exhibits a high fraction (22.54%) of oxygen vacancy‐related defect oxygen species as indicated by combined X‐ray photoelectron spectroscopy and electron paramagnetic resonance measurements. These defect sites facilitate VO ²⁺ /VO ₂ ⁺ adsorption and accelerate vanadium redox kinetics. At the same time, the synergistic interaction between CoSnO ₃ nanocubes and rGO enhances electron transport, increases active‐site exposure, and promotes ion diffusion. When deposited onto heat‐treated graphite felt (HGF), the CoSnO ₃ /rGO‐modified positive electrode exhibits reduced overpotential, improved electrochemical reversibility, and stable high‐rate cycling performance in VRFB single cells. The assembled VRFB achieves energy efficiencies of 84.12% at 80 mA cm ⁻² and 74.22% at 160 mA cm ⁻² , significantly surpassing the efficiencies of pristine graphite felt under identical conditions. These findings show that defect‐engineered mixed transition‐metal oxide–carbon hybrids are a promising design strategy for high‐performance VRFB cathodes and offer insights for developing next‐generation large‐scale electrochemical energy storage systems.