Controllable Synthesis Of Nitrogen-Rich Doped Porous Carbon Materials And Study On Supercapacitor Performance

In recent years,porous carbon materials,due to their diverse structures,high specific surface area,abundant and controllable pore structure,and stable physicochemical properties,have found extensive applications in electrochemical fields such as energy storage and conversion.Studies have shown that factors such as the degree of graphitization,specific surface area,pore structure,pore size distribution,and heteroatom doping of porous carbon materials can all influence the electrochemical properties of the material.Generally,increasing the specific surface area of the material is an important factor in improving its supercapacitor performance.A high specific surface area allows for more thorough contact between electrolyte ions and active sites on the material surface,thereby enhancing the supercapacitor performance of the material.Interconnected pores are more conducive to the transport of electrolyte ions,affecting the supercapacitor performance of the material,and heteroatom doping can also significantly increase the energy density of the carbon material.Among these,nitrogen is the most commonly used dopant because nitrogen-containing functional groups can significantly improve the surface polarity,conductivity,and electrochemical activity of the carbon matrix,which plays an important role in supercapacitors.In particular,pyridinic nitrogen and pyridone/pyrrolic nitrogen in the carbon skeleton can undergo reversible redox reactions during the charge and discharge process of a supercapacitor,producing Faradaic pseudocapacitance and thereby enhancing the performance of the supercapacitor.However,the synthesis and application of nitrogen-doped porous carbon materials still face several difficulties:(1)In most cases,nitrogen-doped porous carbon is prepared by introducing nitrogen onto the carbon skeleton via hightemperature ammonia treatment,and the nitrogen content of these materials is usually too low(below 5 wt%).Furthermore,the nitrogen atoms introduced into the carbon main chain by NH3 activation are unevenly distributed,and the types of nitrogen are uncontrollable.(2)Nitrogen-doped porous carbon materials are synthesized by in situ doping with nitrogen-containing materials(such as melamine,phenylenediamine,aniline,acetonitrile)as carbon precursors.The pore structure and pore size distribution of materials synthesized by this method are uncontrollable and the reaction system has many limitations.These limitations greatly restrict the synthesis and application of high nitrogen-doped porous carbon materials.Based on the above problems,this paper designs and prepares a series of porous,nitrogen-doped carbon electrode materials with tunable pore structures,and systematically studies the relationship between pore structure,specific surface area,nitrogen content and nitrogen species,and supercapacitor performance.We adopted a strategy of ethylenediamine-assisted co-assembly to synthesize nitrogen-doped porous carbon with a tunable pore structure,high nitrogen content,and a high proportion of pyridinic nitrogen.Ethanol and water were used as solvents,2,6-diaminopyridine as the nitrogen source(DAP),tetraethyl orthosilicate(TEOS)as a structure-assisting agent,ethylenediamine(EDA)as a linking agent,and Na OH as an alkaline catalyst,and together with the polymerization of glyoxal,hollow nitrogendoped porous carbon spheres(H-NPCs)were synthesized.In the absence of EDA but with the addition of glyoxal,semi-shell nitrogen-doped carbon spheres(H-NCs)were synthesized.By adding glyoxal but without Na OH,indented nitrogen-doped porous carbon spheres(I-NPCs)were prepared.By adjusting the polymerization monomer to formaldehyde and without the addition of Na OH,three-dimensional nitrogen-doped porous carbon(3D-NPC)can be obtained.By changing the carbonization temperature,the nitrogen content can be adjusted from 11.4 wt% to 19.3 wt%.By changing the amount of EDA added,the shell thickness and specific surface area of H-NPCs can be precisely controlled.By changing the volume ratio of ethanol/deionized water,the cavity diameter and pore structure of H-NPCs can be controlled.By reducing the ethanol/water ratio,the pore size of 3D-NPC can be controlled.We tested the supercapacitor performance of the synthesized high nitrogen-doped porous carbon materials and discussed the effects of carbonization temperature,shell thickness,pyridinic nitrogen species,and pore structure on the supercapacitor performance of the materials.The prepared high nitrogen-doped porous carbon materials exhibit high specific capacitance performance,good rate performance,and excellent cycle stability as supercapacitor electrode materials due to their unique pore structure,high surface area,high nitrogen content,and high proportion of pyridinic nitrogen.