Ultrahigh-surface-area nitrogen-doped hierarchically porous carbon materials derived from chitosan and betaine hydrochloride sustainable precursors for high-performance supercapacitors

Chitosan is a deacylation product from chitin, which can be easily sourced from the exoskeletons of arthropods and shells of cephalopods. Betaine hydrochloride is one of the important derivatives from glycine betaine and one of the main co-products of the sugar beet industry. In this work, a polyelectrolyte was easily prepared in water from chitosan with betaine hydrochloride, which can be used as a sustainable precursor for preparation of ultrahigh-surface-area nitrogen-doped (N-doped) hierarchically porous carbon materials via carbonization and activation with satisfactory electrochemical properties in high-performance supercapacitors. The as-prepared hierarchically porous carbon materials have an ultrahigh specific surface area (up to 3300 m2 g(-1)), large pore volume (up to 2.24 cm3 g(-1)) and a content of 17.61 at% oxygen and 2.23 at% nitrogen. When used as electrode materials for symmetric supercapacitors in 6 M KOH electrolytes, the obtained carbon material shows a significantly high gravimetric capacitance of up to 367 F g(-1) at a current density of 0.1 A g(-1). Moreover, the assembled supercapacitor delivers a relatively high energy density of 12.7 W h kg(-1) and a power density of 25 W kg(-1), as well as a high cycling stability of 94% capacitance retention after 20 000 cycles.