Hemp-derived hierarchically porous carbon cathode enabling high energy storage for advanced zinc-ion hybrid capacitor

Zinc-ion hybrid capacitors (ZIHCs) combining the advantages of secondary metal-ion batteries and supercapacitors, show promising application prospects in energy storage realm due to its intrinsic low cost, safety and scalable production. However, the low charge storage capability of carbon cathode does not match the high capacity of zinc anode, resulting in unsatisfied energy supply and poor cycling durability. The designing and tuning of carbon materials microstructure is one of the key breakthroughs for achieving high performance ZIHCs. Herein, a biomass porous carbon rich in oxygen functional groups (HRPC-X) was controllably prepared by pyrolysis of HEMP assisted with high temperature chemical activation. The features of high specific surface area, hierarchically porous structure and abundant oxygen-containing functional groups of HRPC-4 can not only provide abundant active sites and shorten ion/electron transfer distance but also improve the surface wettability and pseudocapacitance contribution. Hence, the as-prepared HRPC-4 demonstrates a superior capacitance performance in both KOH and Zn(CF₃SO₃)₂ aqueous electrolyte. Specifically, the as-assembled Zn//2 M Zn(CF₃SO₃)₂//HRPC-4 ZIHC device delivers a high energy density of 168.8 W h kg⁻¹, a power output of 45 kW kg⁻¹ and an excellent cycling stability with as high as 95.2 % of capacity retention after 10,000 cycles at 5 A g⁻¹.