Effects of metal-coupled exogenous nitrogen on the performance of supercapacitors based on biomass carbon materials.

Supercapacitors offer great potentials in the field of energy storage due to their high power density, high charge and discharge efficiency, and excellent cycle performance. The relatively low specific capacitance limits their further development and application. Insertion of heteroatoms is one of the most effective strategies to improve the specific capacitance. In this study, different metal salts (Fe/Co/Ni)-coupled N-doped biochar materials, MS-X-N (X represents the metal element), were produced from cornstalk as carbon source and urea as nitrogen source by the chemical activation method to explore the effect of metal(Fe/Co/Ni)- N coupling on the physicochemical and electrochemical properties of biochar. The prepared samples had good pore structure and their specific surface areas were between 1500 and 1800 m 2/g. The doping elements were all successfully inserted into the biochar with the metal content of 0.3%∼0.9% and N content of 2.5%∼4.0%. In the electrochemical test of biochar with a current density of 0.5A/g, MS-X-N samples showed specific capacitance of 180–450 F/g with MS-Co-N giving the best result. Under the combined influence of Co and N, the capacitance of biochar was significantly enhanced. At the current density of 0.5 A/g, the MS-Co-N sample had a specific capacitance 443.94 F/g, an energy density was 15.41 Wh/kg, and a power density was 250.19 W/kg. The findings of research provides a new avenue for the fabrication of high-efficiency supercapacitors. • The effects of different metal-coupled N doping on the microstructure of biochar are different. • Compared with Fe/Ni, Co-coupled N doping further increases the N content of biochar. • Co-coupled N doping can effectively improve the capacitive properties of biochar. • Co-coupled N doping makes the modified biochar have higher cycling stability. • The conductivity of biochar is decreased by Co-coupled N doping, while that is enhanced by Fe/Ni-coupled N doping. [ABSTRACT FROM AUTHOR]