Two-step synthesis of B and N co-doped porous carbon composites by microwave-assisted hydrothermal and pyrolysis process for supercapacitor application

A series of nitrogen and boron co-doped porous carbon composites (BNCs) were obtained using quick, easy and environmentally microwave-assisted hydrothermal treatment combined with a pyrolysis process subsequent. Biomass waste of fir bark is used as the carbon precursor, while ammonium pentaborate tetrahydrate is used as both boron (B) and nitrogen (N) source. The synthesis process and characteristics of the developed BNCs are investigated, and the results show that the N and B is successfully doped, generating a synergetic effect on the structure, surface characteristics and electrochemical properties. The BNCs achieves specific surface area up to 955 m 2  g −1 with mainly microporosity, and possess 10–13 % of B and 15~20 % of N content. The gravimetric capacitance values for the electrodes containing BNC-20 active materials is 188 F g −1 at 0.5 A g −1 , 2 times that of non-doped carbon, while maintaining 90% capacitance retention capability after 10,000 charge/discharge cycles. Furthermore, the assembled symmetric cell yielded high performance of volumetric capacitive of 91 F cm −3 at 0.5 A g −1 , superior energy density of 9.33 Wh kg −1 at 400 W kg −1 with 91% capacitance retention after 10,000 charge/discharge cycles at 1 A g −1 . Our work offers a potential relatively low-cost, effective and environmentally design of heteroatoms doped electrode materials with enhanced supercapacitors performance.