Nitrogen and sulfur co-doped porous chitosan hydrogel-derived carbons for supercapacitors

To achieve high-performance supercapacitors, nitrogen and sulfur co-doped porous chitosan hydrogel-derived carbons (CHC-SK) are successfully prepared by one-step carbonization. In the synthesis, two effective strategies of structure design and heteroatom doping are both used to increase capacitance of carbon materials. To control and design of structure, potassium citrate as a novel pore-former is introduced into chitosan hydrogel systems. It plays three roles in pore formation and thereby can be effective to optimize structure and improve surface area of CHC-SK. In addition, thiourea as binary doping of nitrogen and sulfur can effectively maximize the pseudocapacitance of CHC-SK. Therefore, CHC-SK with large surface area (1596.4 m(2) g(-1)) and high heteroatom content (5.43% for nitrogen, 2.62% for sulfur) show excellent electrochemical performances. The specific capacitance of CHC-SK reaches up to 366.8 F g(-1) at 0.5 A g(-1). Even at the high current density of 10A g(-1), its capacitance retention is 97.1% for 10,000 cycles. This simple strategy for the synthesis of nitrogen and sulfur co-doped porous chitosan hydrogel-derived carbons with high specific capacitance has promising applications in the future.