Conversion of wood waste into nitrogen-doped graphite-like multiporous carbon with high specific surface area and electrical conductivity for high-voltage supercapacitors

Abstract

A novel synthesis method is proposed for preparing nitrogen-doped graphite-like multiporous carbon (N-GMPC) from wood biochar using oyster shell powder as an activating agent without using inert gas. The proposed method is demonstrated using three different biochar precursors: Acacia confusa, Leucaena leucocephala, and a mixture of scrap wood. The N-GMPC derived from Acacia confusa exhibits a large specific surface area of 1638 m² g⁻¹, a high nitrogen content of 4.2 wt%, and a good electrical conductivity of 9.37 S cm⁻¹. In addition, organic supercapacitor applications with 1.0 M TEABF₄/PC electrolyte demonstrate a specific capacitance of 129 F g⁻¹ and a capacitance retention rate of 90% in the high voltage range of 2.3 to 2.7 V after 30 000 cycles. In contrast, commercial porous carbon shows a capacitance retention rate of just 29% under equivalent conditions. Notably, the N-GMPC overcomes many limitations of traditional porous carbon materials in supercapacitors, such as an amorphous structure and poor conductivity, which hinder its rate performance and cycle life. Even without conductive additive (Super P), the N-GMPC maintains a similar performance. In other words, the N-GMPC has good intrinsic conductivity. In high-voltage electrolytes up to 4.0 V (1.0 M SBPBF₄/ADN), the N-GPMC maintains an impressive performance, with a specific capacitance of 164 F g⁻¹, an energy density of 61.19 W h kg⁻¹, a power density of 23.22 kW kg⁻¹, and a capacitance retention of 80% after 10 000 cycles. Overall, the synthesis strategy proposed in this study offers a novel pathway for deriving sustainable energy storage materials from natural waste biomass resources.