Conversion of biomass waste to multi-heteroatom-doped carbon networks with high surface area and hierarchical porosity for advanced supercapacitors

Carbon represents one of the most prominent materials for energy applications. It is always desirable to achieve high value-added carbon materials from biomass wastes. Herein, the advanced carbon materials with multi-heteroatom-doping, high surface area and hierarchical porosity are prepared by hydrothermal conversion and post-activation of silkworm excrement, an agricultural waste. Owing to their unique composition and porosity, the carbon networks show a specific capacitance as high as 412 F g⁻¹ in 6M KOH electrolyte at a current density of 0.5 A g⁻¹. The symmetric supercapacitor device can deliver a high energy density up to 28.78 Wh kg⁻¹ at a power density of 300 W kg⁻¹ with a wide voltage window of 2.0 V in 1M Na₂SO₄ aqueous electrolyte. It also exhibits superb cycling stability with a capacitance retention of 92.9% for 10000 cycles. This work demonstrates a facile and eco-friendly strategy to transform biomass wastes into superior carbon electrode materials for high-performance supercapacitors.