Nitrogen-doped Carbon Paper as Electrodes for Vanadium Redox Flow Batteries

To improve the electrochemical activity of carbon paper (CP) for vanadium redox flow batteries, CP was modified by heat treatment in atmosphere of NH 3 at 600 (NCP-600) and 900℃ (NCP-900), respectively.The FTIR results indicate that the nitrogenous groups have been introduced on the surface of CP by modification successfully.Compared with the pristine sample, the water contact angle of NCP-900 decreases from 120.5° to 99.7°, indicating the improved hydrophilicity of CP by nitrogen doping.The SEM results show that there is no obvious morphology change on the surface of CP after nitrogen doping, which do not affect the mechanical property.The electrochemical activity of CP is enhanced significantly by nitrogen doping.The oxidation current peak of V(Ⅳ)/V(Ⅴ) couple on NCP-900 is 92.1 mA, much higher than that of pristine sample (68.9 mA).The cells with NCP-900 and pristine sample as electrodes were assembled and the charge-discharge performance was evaluated.The energy efficiency of cell with NCP-900 as electrode at a current density of 20 mA/cm 2 is 83.73%, 2.59% larger than that with the pristine sample.The improved electrochemical performance of nitrogen-doped carbon paper is due to the increased active sites and the enhanced hydrophilicity provided by the introduced nitrogenous groups.