Nanostructured N-doped carbon materials derived from expandable biomass with superior electrocatalytic performance towards V2+/V3+ redox reaction for vanadium redox flow battery

Vanadium redox flow battery (VRFB) is one of the most promising large-scale energy storage systems, which ranges from kilowatt to megawatt. Nevertheless, poor electrochemical activity of electrode for two redox couples still restricts the extensive applications of VRFB. Compared with VO2+/VO2+ redox reaction, V2+/V3+ reaction plays a more significant role in voltage loss of VRFB owing to slow heterogeneous electron transfer rate. Herein, N-doped carbon materials derived from scaphium scaphigerum have been developed as negative electrocatalyst by hydrothermal carbonization and high-temperature nitridation treatments. The undoped carbon material hardly has electrocatalytic ability for V2+/V3+ reaction. Based on this, N-doped carbon materials with urea as nitrogen source exhibit excellent electrocatalytic properties. And the material nitrided at 850 °C (SSC/N-850) exhibits the best performance among those from 700 to 1000 °C. SSC/N-850 can accelerate the electrode process including V2+/V3+ reaction and mass transfer of active ions due to the large reaction place, more active sites, and good hydrophilicity. The effect of catalyst on comprehensive performance of cell was evaluated. SSC/N-850 can improve the charge–discharge performance greatly. Utilization of SSC/N-850 can lessen the electrochemical polarization of cell, further resulting in increased discharge capacity and energy efficiency. Discharge capacity and energy efficiency increase by 81.5% and 9.8% by using SSC/N-850 as negative catalyst at 150 mA cm−2, respectively. Our study reveals that the developed biomass-derived carbon materials are the low-cost and efficient negative electrocatalyst for VRFB system.