Green preparation of high active biochar with tetra-heteroatom self-doped surface for aqueous electrochemical supercapacitor with boosted energy density

Developing self-doped carbon electrode material with natural pore system is extremely important to achieve high energy-density for supercapacitors. Herein, we present a promising renewable strategy to convert the biomass, Suaeda Glauca Bunge (SGB), into porous biochar through pore opening by alcohol and pore filling by NaCl crystal. The resultant biochar SGB-700 shows a specific surface area of 684 m2·g−1 and tetra-heteroatom (N, O, S, Cl) doped surface. Interestingly, the typical biochar SGB-700 displays a high specific capacitance of 638 F·g−1 at the current density of 0.5 A·g−1 in the electrolyte of 1.0 M H2SO4. In two electrode system, it offers the specific capacitance of 515 F·g−1 at the current density of 0.5 A·g−1, attractive energy density of 30.2 Wh·kg−1 at power density of 164.0 W·kg−1, good rate capability of 76.1 % at 20.0 A·g−1, and perfect cyclic stability of 107.1 % retention after 12,000 cycles charge-discharge. The assembled supercapacitor can power eleven light-emitting diode (LED) bulbs. The study provides a simple and recyclable method to produce tetra-heteroatom co-doped porous biochar for supercapacitors with high energy density.