Wheat-bran-based hierarchically porous biochar as electrode materials for supercapacitors

Biomass-derived carbon materials have been considered one of the ideal electrode materials for supercapacitors. Herein, functioning as electrode materials, wheat-bran-based porous biochar (WBPC) was wielded for supercapacitors utilizing hydrothermally carbonized wheat bran as a carbon source and KMnO4 as the activator under the nitrogen environment for carbonization at 600 °C for 2 h with the mass ratio of 1:1 (KMnO4 to hydrothermally carbonized wheat bran). The Brunauer-Emmett-Teller (BET) analysis showed that the resulting biochar, designated as WBPC1-2-600, possesses a hierarchical porous configuration with a specific surface area of 544 m2 g−1, XRD and Raman spectroscopy demonstrated a certain degree of graphitization occurred in WBPC1-2-600 and X-ray photoelectron spectroscopy (XPS) analysis indicated that heteroatoms of oxygen have been successfully doped into WBPC1-2-600 after KMnO4 activation and modification. Electrochemical tests show that the WBPC1-2-600 electrode has good capacitance properties in the three-electrode system, with a specific capacitance of 312.1F g−1 at a current density of 0.5 A g−1. The symmetrical supercapacitor assembled with the 2 identical WBPC1-2-600 electrodes, denoted as SSC-WBPC1-2-600, has good cyclic stability within a two-electrode system while the capacitance retention rate maintains 91.2% even after 5000 cycles, and exhibits an imminent energy density of 16.63 W h kg−1 when the power density was at 250 W kg−1 and 11.72 W h kg−1 at 10000 W kg−1.