Carboxymethyl chitosan-derived carbon foam with hierarchical pores tuned by potassium tetraborate and potassium carbonate for supercapacitors

Porous carbons have been extensively concerned in energy-storage fields due to their good conductivity, stable chemical and physical properties, and large specific surface area. The fabrication of porous carbons possessing controlled structure and excellent capacitive performance by facile preparation methods is highly desirable. Herein, a nitrogen-doped carbon foam derived from carboxymethyl chitosan is fabricated via a gel-based method with potassium tetraborate tetrahydrate (K2B4O7·4H2O) as the template agent and potassium carbonate (K2CO3) as the activating agent. The as-prepared carbon foam (KBCF) owns hierarchical pores (i.e., macro-, meso-, and micropores) resulting from the synergy of K2B4O7 and K2CO3. Moreover, the doped nitrogen atoms in KBCF originating from the amino groups in carboxymethyl chitosan provide additional pseudocapacitance. As a result, KBCF possesses a large specific surface area (large to ~3231.0 m2 g−1), outstanding specific capacitance (317 F/g at 1 A g−1), and excellent cycle life (retaining 96.3 % of the initial capacitance after 10,000 consecutive charge-discharge cycles). The assembled symmetric quasi-solid supercapacitor (KBCF//KBCF) can deliver a high power density of 25 kW kg−1 at an energy density of 2.35 Wh kg−1 and an energy density of 6.84 Wh kg−1 at a power density of 500 W kg−1. The outstanding electrochemical performance demonstrates a promising prospect of KBCF in high-performance supercapacitor electrodes.