Abstract:

N and P co-doped carbon aerogels(NPCA) were prepared from cattail inflorescence with NH₄H₂PO₄ as dopant by pretreatment with acidic sodium chlorite, ultrasonic cell fragmentation, freeze-drying and carbonization at high temperature. The surface morphology, pore structure, crystalline structure and surface chemical composition of NPCA were characterized by SEM, N₂ adsorption/desorption, XRD and XPS. The effects of doping amounts and carbonization temperatures on the electrochemical properties of NPCA were systematically studied. The results of research showed that NPCA was a three-dimensional network structure that composed of amorphous carbon. The nitrogen element on the surface of NPCA existed in the form of pyridine nitrogen(N-6), pyrrole nitrogen(N-5), graphitization nitrogen(N-Q) and oxidation state of nitrogen(N-X), and the phosphorus element existed in the form of P—O and P—C. The pore structure and surface chemical structure of NPCA were greatly affected by doping amount of NH₄H₂PO₄ and carbonization temperature. The optimum preparation conditions of NPAC were that the mass ratio of cattail-based cellulose to ammonium dihydrogen phosphate was 1∶2 and the carbonization temperature was 800 ℃. The NPAC-2-800 prepared under this condition has rich pore structure and surface functional groups. Furthermore, the specific surface area was 599.88 m²/g, the total pore volume was 0.27 cm³/g, the micropore volume was 0.20 cm³/g, and the average pore size was 3.69 nm, the N and P contents of NPCA were 5.69% and 5.12%, respectively. The electrochemical properties of the NPCA were measured by three electrode system in 6 mol/L KOH solution. The specific capacitance of NPCA-2-800 was 249 F/g at a current density of 1 A/g, which was 133.4% higher than that of the undoped sample(106.7 F/g), and had good rate performance.

Key words: cattail, carbon aerogel, electrochemical performance