Preparation And Capacitive Properties Of Nitrogen-doped Porous Carbon For Electrochemical Supercapacitors

Nitrogen-doped porous carbons (NPCs) have broad application prospects as electrode materials for supercapacitor because the nitrogen functional groups on carbon skeleton can not only provide pseudocapacitance effect but also improve the surface wettability of electrode materials. Heavy organic matter, with high carbon content and high aromaticity, is mainly composed of colloid and asphaltene and easy to polymerization and crosslinking etc., which is suitable as precursor of preparation of various functional carbon materials. In this paper, porous carbons with different pore structures and nitrogen content were synthesized by using asphaltene from coal liquefaction residual as carbon source and melamine as nitrogen source via a hard template method or chemical activation with KOH. The effects of pore structures and surface properties of NPCs on the electrochemical performance were investigated systematically by controlling synthetic process. The main achievements are briefly summarized as follows:Template method:1) Chemical blend carbonization method:NPCs were prepared by mixing prepolymer of melamine and formaldehyde, asphaltene and magnesium citrate, followed by solidification, carbonization and template dissolution. It was investigated that the influences of ratio of template/asphaltene and carbonization temperature on the textural properties, surface characteristic and electrochemical performance. In particular, the sample prepared with a mass ratio of template/asphaltene of3and carbonization temperature of700℃has a specific surface area of1388m2g"1and nitrogen content of4.22wt.%, showing a fairly high capacitance, about260F g"1at a current density of0.1A g-1, still up to214F g-1at a current density of4A g-1. The Capacitance retention retained about92%of the initial capacitance after5,000cycles at a current density of1A g-12) Mechanical blend carbonization method:NPCs were briefly prepared by mixing magnesium citrate and the oxidization of melamine and asphaltene, followed by carbonization and template dissolution. Results show that the sample prepared with carbonization temperature of700℃shows a fairly high capacitance, about209F g-1at a current density of0.1A g-1, which was closely related with higher specific surface area (1003m2g-1) and nitrogen content (3.18wt.%). Compared to two different kinds of preparation in the same conditions, NPCs with the higher surface area and nitrogen content can be obtained using chemical blend carbonization method, while NPCs with the larger pore volume and average pore size can be obtained using mechanical blend carbonization method.Chemical activated with KOH:Nitrogen-doped activated carbons (NACs) were prepared by potassium hydroxide activation of nitrogen enriched carbon precursors (NC), which are derivate from the carbonization of melamine and asphaltene. With the ratio increase of KOH/NC, the specific surface areas of NACs increase from806to2952m2g-1, while nitrogen content decrease from3.58to0.19wt.%. The specific capacitance of NAC-1. with specific surface areas of1264m2g-1and nitrogen content of1.81wt.%, reaches above295F g-1at a current density of0.1A g-1. The capacitance retention retained about94%of the initial capacitance after5.000cycles at a current density of1Ag-1.