Heteroatom-doped hierarchical porous carbon aerogels from chitosan for high performance supercapacitors

Carbon aerogel with various morphology and structural characteristics were prepared from chitosan by freeze drying-carbonization/activation process. The carbon aerogel obtained without activation (CNS-800) exhibited sheet structure and disordered micropores, N mostly existing in the forms of N-5 and N-6 groups. After phosphoric acid activation (CNS_P-800), a 3D-honeycomb structure with long-range ordered pore channels was presented, with N-X being the main nitrogen-containing groups, some P-O/P=O and PC groups were also detected. KOH activation of CNS (CNS_K-800) led to the formation of incomplete 3D-mesh structure and some graphite-like structure, which is the most unordered structure attributed to the high intense of KOH activation. All the samples showed micro-mesoporous structure, the specific surface area of CNS-800, CNS_k-800 and CNS_P-800 were 421, 1215 and 1475 m²/g, respectively. When used as electrode in the three-electrode supercapacitor, the capacitance values of 171, 318 and 416 F/g were obtained at 1 A/g in 1 M H₂SO₄ electrolyte for CNS-800, CNS_K-800 and CNS_P-800, with the pseudo capacitance contribution rates of 25.4%, 31.6% and 37.6% respectively. Additionally, the capacitance values were 98, 126 and 168 F/g in the two-electrode system respectively, and their energy densities reached 3.35, 4.69 and 6.36 Wh/kg at a power density of 25 W/kg accordingly.