Rapid synthesis of chitin-based porous carbons with high yield, high nitrogen retention, and low cost for high-rate supercapacitors

Summary It is a great challenge to simultaneously achieve high yield, high nitrogen retention, and low cost for chitin-based porous carbons (PCs) while obtaining highly porous structure. Herein, copper (II) chloride dihydrate (CuCl 2 2H 2 O) is innovatively used as the microwave absorber and also porogen for direct synthesis of PCs from chitin via microwave heating. A very short duration of 10 minutes is achieved for this synthesis, because microwave irradiation renders a rapid heating rate of 126°C min −1 during the initial 5 minutes. In addition, the melted CuCl 2 wraps the chitin to preserve its overall structure during synthesis, thus obtaining a yield as high as 36% and a nitrogen retention up to 5.2%. Furthermore, a low temperature of about 600°C that triggers the redox reactions of CuCl 2 into Cu to achieve well-developed porous structure (specific surface area up to 1535 m 2 g −1 ) is observed, suggesting a merit of low cost for this synthesis. The PC-based electrode exhibits not only a high specific capacitance of 227 F g −1 at 0.5 A g −1 in 6 mol L −1 KOH electrolyte but also a good rate capability with a high capacitance retention of 67.7% even at an ultra-high current density of 50 A g −1 . Owing to these promising capacitive performances of PCs, the fabricated supercapacitor can remain 70.1% of the energy density when the power density was dramatically increased by 20 times.