Activated porous carbon derived from walnut shells with promising material properties for supercapacitors

Porous carbons derived from plant biomass have become the most competitive electrode materials for supercapacitors because of their renewability and sustainability. Here, activated carbons from walnut shells were fabricated by KOH activation with different mass loading and thermal pyrolysis process at temperatures between 500 and 900 °C in N₂ air. The obtained activated carbons maintained the inherent structure after synthesis process and developed interconnected micro-, meso- and macro-pores. Not only the unique structure, but also many oxygen-containing functional groups contained were beneficial to enhance the electrochemical properties of porous carbon materials. With the honeycomb-like 3D pore network, carbon electrode materials exhibited a specific capacitance of 186.68 F g⁻¹ at 0.5 A g⁻¹, high rate capabilities and excellent cycling performance with about 100% capacitance retention over 20,000 charge–discharge cycles at 2 A g⁻¹ in 6 M KOH electrolyte. The porous carbon from biomass walnut shells shows the potential of the application in energy storage.