Highly graphitized lignin-derived porous carbon with hierarchical N/O co-doping core-shell superstructure supported by metal-organic frameworks for advanced supercapacitor performance

Porous carbon nanoparticles have been widely utilized as electrode materials for electric double-layer capacitors (EDLCs) owing to their rich microporous and mesoporous structures. Herein, we successfully prepared lignin@ZIF-8 based carbon with hierarchical porous core-shell graphitized superstructure (KGC-EHL@ZIF-8) fabricated by carbonized ZIF-8 NPs as core and lignin derived graphitized porous carbon layer as shell via a two-stage carbonization-graphitization process for advanced supercapacitor performance. The prepared KGC-EHL@ZIF-8 NPs possess a high graphitization degree, high porosity with micro/meso porous hierarchical structure and high content of N/O co-dopants induced by the synergistic effects of ZIF-8 NPs coupling potassium hydroxide (KOH) activation treatment, thus guaranteeing excellent electrochemical performance. As a result, the graphitization degree of lignin-derived porous carbon shell structure increased with KOH ratio, and the maximum specific surface area of 2307.3 m(2).g(-1) was successfully obtained at a mass ratio (KOH/C-EHL@ZIF-8 NPs) of 1:1. The maximum specific capacitance within three-electrode system was 462.6 F.g(-1) at 0.5 A.g(-1) with a porous carbon shell thickness of around 75.25 nm. Moreover, the areal energy density of assembled super-capacitor can reach to 1.95 mWh.cm(-2) at a power density of 27.44 mW.cm(-2). This study put forward a novel strategy to efficiently harness lignin combined with a metal-organic framework for the construction of porous electrodes with hierarchical nanostructure for high-performance supercapacitors.

Automated summary

Porous carbon nanoparticles with hierarchical porous core-shell graphitized superstructure (KGC-EHL@ZIF-8) were successfully prepared as electrode materials for high-performance supercapacitors. By carbonizing ZIF-8 NPs as core and using lignin derived graphitized porous carbon layer as shell, the resulting KGC-EHL@ZIF-8 NPs exhibited high graphitization degree, high porosity, and high content of N/O co-dopants, ensuring excellent electrochemical performance.