A Bifunctional Nitrogen‐Doped Electrode with High Catalytic Activity and Stability for Energy‐Efficient V ^3.5+ Electrolyte Production and High‐Performance Vanadium Redox Flow Batteries

ABSTRACT Flow electrolysis offers an effective solution for producing vanadium electrolytes, delivering superior purity and quality compared to traditional batch methods. However, this approach is challenged by high energy demands and limited long‐term durability. In this context, a surface‐architecting strategy that leverages polyaniline self‐assembly is introduced to construct a nitrogen‐doped carbon nanofiber network‐modified graphite felt (NGF). The N‐doped porous nanoarchitecture provides a high density of redox‐active sites and highly accessible mass‐transfer channels. Electrochemical analyses demonstrate that NGF exhibits exceptional electrocatalytic activity toward both the V ⁵⁺ /V ⁴⁺ and V ⁴⁺ /V ³⁺ redox couples. The flow electrolyzer configured with the NGF achieves a 60.25% reduction in energy consumption per unit conversion rate at 100 mA/cm ² (V ⁵⁺ /V ⁴⁺ ) and 400 mA/cm ² (V ⁴⁺ /V ³⁺ ) than the original graphite felt, and consumes 41.63% lower energy compared to the thermally‐treated graphite felt. Furthermore, the vanadium redox flow battery (VRFB) using NGF as the anode exhibits an energy efficiency of 82.71% at 200 mA/cm ² and superior long‐term stability during charge–discharge cycling. This research provides a new approach to modifying electrodes for preparing vanadium electrolytes and to optimize the operation of VRFBs.