Rapid one-step preparation of hierarchical porous carbon from chitosan-based hydrogel for high-rate supercapacitors: The effect of gelling agent concentration

Herein, chitosan-based hydrogel beads (CHBs) were used to prepare N- and O-enriched hierarchical porous carbon (PC) by microwave heating for only 10 min. Water molecules in CHBs can act as heating carriers, and the resulting steam not only squeeze out air to create an oxygen-free atmosphere but act as physical activating agent to generate pores. Furthermore, the increased temperature contributed to form chitosan-based char, which, in turn, facilitated microwave absorption to further increase temperature. Considering that KOH as gelling agent of CHBs can also generate pores, the effect of KOH concentration on physicochemical properties of PCs was investigated in detail. Significantly, appropriately higher KOH concentration (3–7%) would cause fiercer reactions to achieve more developed porous structure, while excessive KOH concentration (10%) led to over-etching phenomenon and limited the further development on porous structure. The obtained PCs exhibited large specific surface area up to 1743 m 2  g −1 and O, N-enriched structure (O: 25.1%, N: 4.9%). Particularly, the optimized PC-based electrode prepared by using 7% KOH solution showed remarkably high rate capability (89%). This work provides a one-step and cost-effective method to prepare a promising electrode material for high-rate supercapacitors.