Preparation Of Nitrogen-rich Carbon Materials And Their Electrochemical Application

The derivatives porous carbon of metal-organic frameworks（MOFs）and covalent organic frameworks（COFs）have attracted much attention in energy storge devices（supercapacitors）and oxygen reduction reaction（ORR）due to their highly ordered structures,greater surface areas,tunable pore sizes and topologies as well as abundant redox-active porous skeletons.In this paper,nitrogen-rich carbon materials were synthesized by carbonization of hexaazatrinaphthyl monomer,polymer/MOFs composites spheres,and their electrochemical application was studied.1.Firstly,the nitrogen-rich hexaazatrinaphthyl monomer（HATN-3CN）was synthesized to prepare the nitrogen-rich derived materials HATNs(HATN-3CN_oligomer,CTF400,HATN-3CN-C₅₀₀,HATN-3CN-C₈₀₀)by an ionothermal synthesis method in molten Zn Cl₂.The physicochemical properties of HATNs and their performance as electrode material for supercapacitor was studied.With the increase of ionic thermal temperature,HATN-3CN firstly trimerized to form covalent triazine skeleton material,and then turned to nitrogen-rich porous carbon material.HATNs material show different nitrogen content and specific surface area.CTF400 exhibits outstanding supercapacitor performance,showing a specific capacitance of 699F g^-1at the current density of 1 A g^-1,and maintaining a specific capacitance of 186.4 F g^-1at the high current density of 100 A g^-1.The specific capacitance and rate capability of CTF400 are better than those of CTFs-based supercapacitor materials reported.CTF400 also shows excellent cycle stability,with a capacitance retention rate of 90.7%after 10000 cycles in a high current density of 10 A g^-1.HATN-3CN-C₈₀₀shows better rate capability than CTF400,with a high specific capacitance of 109.9 F g^-1at 100 A g^-1.HATNs can be used as electrode material for supercapacitor,especially for high current density.2.The phenolic resin polymer spheres with different internal crosslinking degrees were used as substrates.The different parts of the polymer spheres could be etched by controlling the amount of methanol.After ZIF-67 coating and carbonization,core-shell and hollow-structure Co-carbon composite CS600 and HS600 were obtained.The uniformly distributed cobalt nanoparticles on the surface of CS600 and HS600 were used as catalysts to grown carbon nanotubes.The ORR performance of obtained Co-carbon composite CNT/HS600 and CNT/CS600 were tested.The reduction peak of CNT/HS600 is 0.7754 V,which is closest to commercial Pt/C,and its half-wave potential（0.7872 V）is slightly greater than that of commercial Pt/C.The Zn-air battery with CNT/HS600 as electrode achieves a higher power density of 87.8 m W cm^-2at 112.6 m A cm^-2current density,and has better rate capability than commercial Pt/C.3.In order to further improve the ORR performance of Co-N/C composite electrocatalyst,the catalysts of this system were modified,and their ORR performances were explored:（1）The cobalt content in HS600 and CS600 was increased by solvothermal method with Co²⁺solution,and the effect on their ORR performances were investigated.After solvothermal reaction,the cobalt content of all materials was increased,and the reduction peak potential（0.7872 V）and half-wave potential（0.7832 V）of CS600-Co _H2Oafter hydrothermal reaction were both increased compared with that of CS600.The results showed that the electrocatalytic activity of the catalyst could be improved by increasing cobalt content appropriately.（2）The sulfur-containing conductive polymer PEDOT was introduced into the carbon precursor in situ,and sulfur element was successfully added into the carbon skeleton during the pyrolysis process.While PEDOT could also make ZIF-67 more stable in carbonization to expose more active site,and improve the thermal stability and catalytic activity of the final product（S/CS700 and S/HS700）.Both S/CS700 and S/HS700 have good ORR performance,and the reduction peak potential is very close to that of commercial Pt/C,while the half-wave potential is higher than that of commercial Pt/C.（3）Si/Co/C composite spherical material CNT/Si/HS800 was prepared by introducing silicon nanoparticles into polymer spheres followed by ZIF-67 coating,carbonization and carbon nanotubes growing.Carbon nanotubes increase the nitrogen content and electrical conductivity of carbon materials,external cobalt nanoparticles provide charge transport channels in the ORR process,and silicon nanoparticles favor oxygen adsorption of Si-doped materials in ORR electrocatalysis,which collaborates to improve the utilization rate of active sites in CNT/Si/HS800.It shows higher reduction peak potential（0.8146 V）and half-wave potential（0.7872 V）than commercial Pt/C with good cyclic stability and methanol resistance.The open circuit voltage of the zinc-air battery assembled by CNT/Si/HS800 is slightly higher than that of commercial Pt/C.CNT/Si/HS800 also shows higher discharge current and smaller charging voltage difference.The rechargeable capability and peak power density of the battery are better than those of commercial Pt/C.