Abstract: Phosphoric acid activated carbon, modified by impregnating melamine, was heated at 500, 700,and 900 ℃ to obtain AC-N-500, AC-N-700 and AC-N-900. The feasibility of these activated carbon for electrode material of electric double layer capacitor (EDLC) were investigated. The effects of heat temperatures on the nitrogen-containing surface functional groups and the electrochemical properties of the modified activated carbons were also investigated. Nitrogen adsorption, elemental analysis, X-ray photoelectric spectroscopy, and electrochemical workstation were employed to analyze the pore structure, element contents, nitrogen-containing surface functional groups and electrochemical properties of the activated carbons, respectively. The results showed that the content of nitrogen decreased from 8.49% to 4.16%, and the specific surface area and total pore volume of the modified activated carbon decreased when the temperature increased from 500 ℃ to 900 ℃. It was found that the nitrogen atoms existed in the forms of N-6(pyridinic), N-5(pyrrolic/pyridone), N-Q(quaternary) and N-X(pyridine/N-oxide)on the surface of phosphoric acid activated carbon. The contents of N-6 and N-5 were slightly decreased with the increase of the treatment temperature from 500 to 900 ℃ and were gradually transformed to the N-Q form. The specific capacitance of the electrode material prepared from AC-N-700 could reach 203 F/g, and the material could reduce the resistance between the electrode and the electrolyte, and bring benefit to the conduction of the penetration of ions and charge. This suggested that phosphoric acid activated carbon had the potential as the electrode material of EDLC.

Key words: phosphoric acid activated carbon, melamine, nitrogen-containing surface functional groups, electrochemical properties