Boron-doped And Nitrogen-doped Activated Carbon As Electrode Materials For Supercapacitor

In this paper, phosphoric acid activated carbon was modified by impregnating melam ine followed by heat treatment at the temperatures of 500-900? to study its potential asthe electrode material of electric double layer capacitor(EDLC). The phosphoric acid ac tivated carbon and KOH activated carbon were oxidation by HNO3 followed impregnating boric acid,then by heat treatment at different temperatures. The effect of heat treatment temperature on the nitrogen-containing and Boron- containing surface functional groups ev olution and the electrochemical properties of the modified activated carbons has been inv estigated. Nitrogen adsorption, elemental analysis, X-ray photoelectric spectroscopy, and el ectrochemical workstation was employed to analyze the pore structure, element contents, nitrogen-containing surface functional groups and electrochemical properties of the activate d carbons, respectively.The results show that the nitrogen-containing and Boron-containing surface functional groups of the modified activated carbon reducing resistance between t he electrode and electrolyte benefit to the conduction of the penetration of ions and char ge.The nitrogen-containing and Boron-containing functional groups have abity of gain and lose electron can arise Faraday constraint capacity through Redox reaction, improve the specific capacitance of activated carbon as a supercapacitor electrode materials.The main conclusions are as follows:(1)The contents of nitrogen of activated carbon is decreased with the heat treatment te mperature increase, the AC-N-500 compare with AC-N-900 the contents of nitrogen from8.49% change to 4.16%.Melamine modified activated carbon specific surface area and to tal pore volume are decreased. the nitrogen atoms exists in the forms of N-6(Pyridinic), N-5(Pyrrolic/pyrydone),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 in the treatment temperature from 500 to 900 ?and were gradually tra nsformed to the N-Q form, the N-Q and N-6 is the main functional groups of the modif ied activated carbon.(2)The nitrogen-containing functional groups increased the specific capacitance of the m odified activated carbon. The AC-N-700 can be prepared electrode material with specific capacitance up to 196F/g at the current density of 0.1A/g. It's suggested that Phosphoric acid activated carbon has the potential of electrode materials for electric double layer cap acitor.(3)The higher the heat treatment temperature the better boron doping in the activated c arbon, different of activated carbon were modified by boric acid, the contens of boron of the AC-B-900 can up to 2%; The degree of graphitization and conductive ability of acti vated carbon increases with the heat treatment temperature increase, but the pore structure was slightly worse.(4)The activated carbon oxidation by HNO3 were doped boron well. The surface area a nd pore volume of activated carbon were significant reduction by oxidation. The acid acti vated carbon oxidation by HNO3 introduced a large number of oxygen-containing functio nal groups in the activated carbon, which were fall off from the surface of carbon at hig h temperatures, exposed more highly active sites reaction with boric acid prepared 3.63%boron-containing activated carbon. The contents of boron of activated carbon are increas ed by oxidation, the boron elements in the activated carbon with form of BCO2, BCO2 a nd BC3.(5)The oxide Boron-doped modified effectively improve the specific capacitance of the activated carbon electrode. The boron-doped modified activated carbon AC-OB-800 and K AC-OB-800 was used as electrode materials for supercapacitor have high specific capacita nce up to 179F/g and 186F/g, respectively. It's suggested that boron-doped activated carb on has the potential of electrode materials for electric double layer capacitor.(6)The oxide Boron-doped modified effectively improve the per unit area capacitance o f the activated carbon electrode.Compared with unmodified activated carbon, the per unit area capacitance of the boren-doped cativated carbon AC-O-B-800 and KAC-o-b-800 incr eased 2.11 times and 2.35 times respectively. The utilization rate of specific surface area increased significantly; Surface wettability of boron-doped activated carbon was improved, the impedance between electrolyte and electrode interface was reduced, boron functional g roups produce Faraday constraint capacitance can effectively improve the specific capacita nce of activated carbon.