Lignin hydrogel-derived hierarchical porous carbon materials using low dosage of alkaline activation agents for high-performance zinc-ion hybrid supercapacitors

Zinc-ion hybrid supercapacitors is a new type of electrochemical energy storage device that could realize high power density and high energy density . However, porous carbon cathode has a high cost of production due to the expensive precursors and excessive consumption of activation agents. Here, a hierarchical porous carbon was prepared by one-step carbonization of lignocellulose-based hydrogels containing alkaline activation agent. This strategy enables the activation agent to be uniformly dispersed in the lignocellulose precursor, which effectively utilizes the activation agent and thus reduces the amount of the activation agent (w(KOH)/w(precursor) <1). Moreover, the porous carbon could partially retain the macroporous and mesoporous structures formed in the lignocellulose-based hydrogel. The obtained porous carbons feature abundant mesopores (average pore sizes of ∼2.0 nm and mesopore ratio of 15.0 % – 79.8 %) and high specific surface areas (1358–1819 m 2  g −1 ). The zinc-ion hybrid supercapacitors with an obtained porous carbon cathode displayed a specific capacitance of 292.4 F g −1 , high rate capability, and long cycle stability (95.4 % capacitance retention after 12,000 cycles at 2 A g −1 ). In addition, we found that the pores larger than 0.65 nm could improve the storage efficiency of zinc ions.