Eutectic salt-assisted preparation of pine wood-based N,O doped self-supported carbon electrodes for high-performance supercapacitors

Abstract

The electrode is a crucial component of supercapacitors, and the development of low-resistance, high-performance supercapacitor electrode materials is a significant challenge. Utilizing the vertical channel structure inherent to wood, adjusting the pore structure, and introducing heteroatom functional groups are considered important approaches to improving the performance of self-supporting supercapacitor electrodes. In this study, pine wood was used as a precursor, and a nitrogen–oxygen co-doped self-supporting carbon electrode was synthesized using low-melting eutectic salts KNO₃ and NaNO₃ combined with a two-step heating pyrolysis process. The presence of eutectic salts and the gentle heating procedure effectively inhibited the deformation of pine wood during carbonization, optimized the pore structure, and introduced heteroatoms. The resulting KNCW-7 exhibited a specific surface area of 420.1 m² g⁻¹, with 17.04% oxygen atom content and 2.67% nitrogen atom content. At a current density of 5 mA cm⁻², it demonstrated a specific capacitance of 7.42 F cm⁻² and a rate capability of 69.27% at current densities ranging from 5 to 50 mA cm⁻². The assembled symmetric supercapacitor KNCW-7//KNCW-7 displayed a high energy density of 400 μWh cm⁻² at a power density of 2.5 mW cm⁻². After 30 000 cycles, it still retained 96.9% of its capacitance, demonstrating excellent cycling stability.