Soybean protein-derived N, O co-doped porous carbon sheets for supercapacitor applications

Abstract

Biomass-derived heteroatom doped porous carbon is a hot electrode material for supercapacitors. Herein, nitrogen and oxygen co-doped porous carbon sheets are prepared by one-step carbonization-activation of hybrids of soybean protein isolate and zinc chloride (ZnCl₂). The effect of the mass ratio between the activator and carbon precursor on the microstructure as well as the electrochemical performance of the materials is investigated. The activated samples show enhanced specific surface area, preferably up to 1034.33 m² g⁻¹, which is dominated by micropores and mesopores. More interestingly, ZnCl₂ incorporation can improve the doping rate of nitrogen and oxygen elements from 4.5 at% to 6.37 at%, and 12.89 at% to 13.58 at%, respectively. Ultimately, the porous carbon sheets exhibit good capacitive performance in 6 M KOH electrolyte, and the specific capacitance could reach 210.47 F g⁻¹ in a three-electrode system. In a two-electrode system, a capacitance retention of 93.02% can be achieved after 10 000 cycles at 20 A g⁻¹. In addition, the optimized sample shows a maximum energy density of 16.27 W h kg⁻¹ and a maximum power density of 8.44 kW kg⁻¹. This work indicates that the soybean protein-derived porous carbon sheets are promising electrode materials for supercapacitors.