Sustainable biomass-based hierarchical porous carbon for energy storage: A novel route to maintain electrochemically attractive natural structure of precursor.

The development of sustainable and renewable energy storage devices with low cost and environment friendly features is an extremely urgent issue that needs to be solved. Herein, low-cost and sustainable biomass chitin, possessing natural fibrous, O/N-enriched and porous structure, was employed as a porous carbon (PC) precursor. However, a huge challenge in PC preparation is to maintain the natural electrochemically attractive structure of chitin while obtaining highly porous structure. In this study, by utilizing the molten protecting effect and micropore-creating ability of CuCl 2HO, the obtained PCs maintain the natural structure, achieve high yield (46%), and simultaneously develop hierarchical pores with a specific surface area range of 1635-2381 m g, a tunable micropore volume ratio range of 63.5-96.8%, and high surface O/N contents (N: 3.1-9.0 wt% and O: 10.5-12.8 wt%). Benefiting from these excellent properties, optimized PC achieves a high specific capacitance of 286 F g at 0.5 A g and a remarkably high rate capability of 88% at 10 A g; moreover, it even exhibits a rate capability of 80% at an ultrahigh current density of 50 A g. The optimized PC-based supercapacitor assembled in NaSO electrolyte shows a high energy density of 15.41 W h kg at 0.19 kW kg and achieves 76% energy density retention when the power density increased tenfold. Thus, this study presents a new way to fully utilize biomass, especially with electrochemically attractive natural structure, for developing advanced energy storage devices.