Nitrogen And Sulfur Co-doped Porous Carbon Electrode Derived From Coal Based Heavy Organic Matters

Porous carbon has been widely used in catalyst support, electrode materials and electro-catalysis for its thermal stability, chemical inertness, good conductivity and large surface areas in constrained space. Surface property is one of the most important factors on its performance. Chemical doping by non-carbon atoms is an efficient way to improve the surface properties of carbon materials and the synergist effect between the doped heteroatoms will endow porous carbon with special ability. Heavy organic matters are composed of asphaltene and pre-asphaltene, which are good precursors for porous carbon. In the thesis, to transfer coal liquefaction residue (CLR) into high value-added matters, nitrogen and sulfur co-doped porous carbon was synthesized from heavy organic matters which derived from CLR. And the relationship between the surface properties and the electrochemical performance of the as-prepared porous carbon was studied. The main contents and results of this thesis are summarized as follows:N doped porous carbon, S doped porous carbon, un-doped porous carbon and N, S co-doped porous carbon were synthesized from modified heavy organic matters which contain sulfur or/and nitrogen atoms by using the in-situ prepared magnesium oxide as the template. The proposed N, S co-doped porous carbons own a BET specific surface area as high as 1540 m2 g-1, a total pore volume over 0.93 cm3 g-1, a nitrogen content with 3.7 wt%, and a sulfur content with 1 wt%.In order to investigate the influence of surface properties of carbon materials on its supercapacitor performance, the supercapacitor performance of the as-prepared porous carbons were tested. Results showed that:the doped porous carbon showed better performance than the pure porous carbon by improving the conductivity of the materials and providing pseudo-capacitance. And NSAC-700 carbon showed the best performance among all the samples. The results of electrochemical measurements demonstrated that the specific capacitance of the NSAC-700 was 294.8 F g-1 in a current density of 100 mA g-1 and 186 F g-1 in a current density of 2 A g-1, and exhibited 90% capacitance retention at 1 A g-1 after 5000 times.In order to illustrate the effect of surface properties of carbon materials on its electro-catalysis performance, the catalytic activity of the samples for oxygen reduction reaction were tested. Results demonstrated that:the catalytic activity of the samples were improved by chemical doping, and the increase of activity sites on the surface of the materials resulting from the synergistic effect of nitrogen and sulfur atoms led to better electro-catalysis performance than the un-doped porous carbon. The limiting current density of NSAC-900 electrocatalyst was as high as 5.8 mA cm-2 and it also possessed high stability (85% activity retention after 20000s continuous testing) and good methanol tolerance in alkaline environment.