Preparation of ultrafine microporous nitrogen self-doped chitosan (CS) carbon aerogel based on a Zn-Zn system for high-performance supercapacitors

Abstract

In light of the depletion of fossil resources, global warming, and other energy and environmental challenges, the utilization of biomass as an energy storage solution holds tremendous promise. In this research, Chitosan (CS)/CH3COOH/(CH3COO)2Zn hydrogels were produced through a cross-linking process that involves both ionic bonding and hydrogen bonding. Subsequently, CS carbon aerogels with extremely fine microporous structures were manufactured via freeze-drying, carbonization, and activation processes utilizing the Zn-Zn system. The dehydrating agent and activator used was ZnCl2, whereas in situ doping of Zn2+ in the carbon precursor functioned as an activation assistant. The activated CS carbon aerogel ACS-Zn20-700 prepared at 700 °C had a specific surface area of 857.47 m2/g, a microporous ratio of 89.44%, a pyridine-N content of 35.58%. The distribution of micropores and ultrafine pores facilitates effective connection and ion transport at the electrode–electrolyte interface, leading to an increase in the number of active sites in carbon materials and ultimately improving their specific capacitance. Nitrogen-containing groups also provided additional pseudocapacitance. In a three-electrode system, ACS-Zn20-700 obtained a specific capacitance of 380.8F/g at the current density of 0.5 A/g. The ACS-Zn20-700 supercapacitor in the two-electrode system had an energy density of 12.8 kW h−1 (at 125 W kg−1) and a capacitance retention rate of 85.27% (at 10,000 cycles). The findings of this work serve as a useful reference for the development of environmentally friendly biomass-derived carbon aerogel materials as potential candidates for supercapacitor electrode applications.