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 m2·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 supercapacitor 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.