Nitrogen‐Doped Carbon Felt as an Electrode Material for Vanadium Flow Batteries

Abstract Vanadium flow batteries (VFBs) are well suited for energy storage due to the attractive features of high safety and long cycle life. Electrodes are a key component of a VFB, directly affecting the energy efficiency and power density of the battery. However, the carbon felt electrode commonly used suffers from poor hydrophilicity and electrochemical activity. Herein, a simple ammonium sulfate hydrothermal method was presented to improve the electrochemical activity and hydrophilicity of carbon felt. In the design, hydrophilic nitrogen‐containing and oxygen‐containing functional groups were introduced in the hydrothermal process, in favor of optimizing the hydrophilicity of carbon felt. The doping of nitrogen with negative charge density and the increasing defects promoted the electrochemical reactions of vanadium ions. Furthermore, the effects of the experimental parameters on the performance of the carbon felt and the battery were carefully studied. As a result, the VFB with 90‐1 nitrogen‐doped carbon felt exhibited the best performance; the energy efficiency achieved 87.34 % at the current density of 80 mA/cm 2 , which was 3.91 % higher than that with the original one.