Constructing hybrid nitrogen/oxygen-rich surface and hierarchically porous in lignite-based activated carbons as supercapacitor electrode by in-situ soda ash activate strategy

Abstract

Coal-based activated carbon materials have the limitations of low specific surface area and limited ion mobilization rate, restricting their practical applications. In this study, porous coal-based activated carbon electrodes were prepared via chemical activation using lignite as a precursor for electrochemical energy storage. Using response surface methodology (RSM), the optimal conditions for preparing porous lignite-based activated carbon were identified: an activation temperature of 856 °C, an activation time of 2.6 hours, and a Na2CO3-coal mass ratio of 4.1:1. The pure alkali carbonization process enriched the activated carbon's three-dimensional pore structure, creating numerous ion-transport channels. The best sample (CAC-3) achieved a surface area of 1847.3 m2 g−1. Process optimization enhanced its electrochemical performance, resulting in a specific capacitance of 219.7 F g−1 at 1 A g−1. It maintained good cycling performance after 5000 cycles in a 6 M KOH aqueous solution at a current density of 10 A g−1. In a two-electrode system, the specific capacitance was 175.3 F g−1 at a current density of 1 A g−1. This study offers new insights for advanced energy storage technologies.