Preparation Of Al-based MOF-derived Nitrogen-doped Porous Carbon And Related Electrochemical Properties

In recent years,the development and utilization of new energysources have become one of the effective solutions in tackling global energy shortage and severe environmental pollution problems.Supercapacitors and lithium-ion batteries have received extensive attention from researchers as good energy storage devices.Supercapacitors have a very broad application prospect as a bridge between traditional capacitors and lithium-ion batteries in lots of application areas.Compared with secondary batteries,they have higher power density,longer cycling life and wider operating temperature range.And the electrode material is the key factor for the improvement of electrochemical performance.In this paper,in order to solve the problems of irrational pore structure,poor surface accessibility,and low capacity of currently widely used porous carbon materials,we prepared the ordered hierarchical porous carbon materials via the carbonization of Al-MOF and nitrogen-doped materials with a facile method.The research content of this thesis mainly involves the development of carbon-based electrode materials derived from Al-based metal organic framework materials,nitrogen doping treatment of porous carbon materials,and one-step synthesis of double-nitrogen source tubular porous carbon.The details are as follows:(1)An aluminum-based MOF precursor(Al-MOF)was synthesized by hydrothermal method using aluminum nitrate nonahydrate(Al(NO3)3·9H2O and Trimesic acid as raw materials)and pyrolyzed in a nitrogen atmosphere to obtain porous carbon material(PC)with uniform morphology and specific pore structure.The effects of different reactant ratios,temperature and keeping time during the synthesis process,and time and temperature of the pyrolysis process on the electrochemical performance of porous carbon were studied.Porous carbon(PC)obtained by a reaction ratio of 1:1,reacting at 160 ° C for 11 hours,and carbonizing at 850? for 2 hours has the best electrochemical performance.The optimized porous carbon provides a specific capacitance(SC)of 275.44 F g-1 at a current density of 1 A g-1.And when the current density is 100 A g-1,it still maintains 82%of the initial capacity,showing excellent rate performance.The material retains 95.8%specific capacitance after 100,000 cycles at a current density of 50 A g-1,showing outstanding cycle stability performance.(2)In this chapter,we conducts nitrogen doping on porous carbon(PC)by polymer-coated post-nitrogen doping method.By optimizing the synthesis conditions,when the coating ratio is 10,the aniline concentration is 0.1 M,and the coating time is 8 h,the complex(PC&PANI)based on porous carbon and PANI is obtained,and then one-step activation with a small amount of NaOH is conducted to prepare nitrogen-doped porous carbon material(ANPC)with optimal performance.The specific capacitance of activated nitrogen-doped porous carbon(ANPC)reaches 346 F g-1 at 1 A g-1,which is better than the porous carbon(PC)and the nitrogen-containing porous carbon(PNPC)obtained by direct activation of PANI.The composite of porous carbon PC and PANI achieves a synergistic effect.The SC of ANPC is 271 F g-1 at 100 A g-1 and in long life recycling and the retention rate is 94.05%after 50,000 cycles at 50A g-1 which show excellent rate performance and cycle stability.(3)In the last chapter,we use melamine crystals(melamine is first dissolved and then cooled to crystallize)as the base,and the surface of the crystals is coated with a layer of polyaniline to form a composite of melamine and polyaniline(ME&PANI).Then the compound(ME&PANI)is carbonized to obtain a double nitrogen source-doped porous carbon material(DNPC).Melamine is both a nitrogen source and a pore-forming agent in the carbonization process.The optimal synthesis conditions as as follows:under the condition of magnetic stirring,the melamine solution is first crystallized for 10 minutes,then the polyaniline is coated with a coating ratio of 1.5,and then the composite is carbonized at 700? for 1.5 h.The SC of DNPC reached 258.3 F g-1 at 1 A g-1 and the capacity retention rate was 95.7%after 20,000 cycles at a current density of 1 A g-1.This method provides a new porous carbon preparation stategy with simple steps,no activation and no complicated post-processing for the future development of high-performance supercapacitors.