Preparations And Capacitance Properties Of Pourous Carbon Doped With Heteroatom

Due to its high specific surface area,developed porous structure and moderate price,porous carbons are the first choice for commercial supercapacitor electrode materials.In this paper,nitrogen-doped microporous carbon,phosphorus-doped mesoporous carbon and nitrogen/phosphorus co-doped porous carbon materials with high specific surface area and hierachical structure were prepared.The effects of the preparation process on the structure and capacitive properties of carbon materials were studied,as well as,the pore-forming mechanism of materials and the influence of N?P heteroatom on the electrochemical performance of carbon materials in different electrolytes were analyzed.Nitrogen-rich microporous carbon materials(NECs)were prepared by direct pyrolysis at 600-900 ? with a nitrogen-containing organic acid salt,ethylenediaminetetraacetic acid,as the carbon precursor.With increasing pyrolysis temperature,the specific surface area and pore volume of carbon materials gradually increased from 457 m2·g-1 and 0.21 cm3·g-1 at 600 ? to 1511 m2·g-1 and 0.98 cm3·g-1 at 900 ?,respectively.However,the N content decreased from 8.69 at%to 0.88 at%.In the 6 M KOH aqueous electrolyte,the specific area capacitance of nitrogen-rich carbon materials decreases with the nitrogen content gradually from 47 uF·cm-2 at 600 ? to 10.1 uF·cm-2 at 900 ?.However,in the 1 M Et4NBF4/AN electrolyte,the specific area capacitance showed a tendency of rising first and then decreasing,and there was no correlation with the nitrogen content.This shows that nitrogen doping can produce larger pseudocapacitance in the inorganic electrolyte system,but in the organic electrolyte system nitrogen can not occur redox reaction,and can not produce pseudocapacitance effect.Phosphorus-doped mesoporous carbon materials(PMCs)were prepared by direct pyrolysis at different temperatures(600-900 ?)with phosphorus-containing organic acid salt-phytate as the phosphorus source and carbon source.A composite structure of carbon-coated Na4P2O7 nanoparticles(5-12 nm)was formed during the pyrolysis of sodium phytate.The mesoporous phosphorus-rich mesoporous carbons were obtained after washed by dilute hydrochloric acid.With the increase of pyrolysis temperature,the specific surface area of carbon materials changed little(884-827 m2·g-1),while phosphorus content slightly increased(0.53-2.34 at%).Electrochemical performance measurments showed that the PMCs exhibited excellent cycling and rate performance in the 6 M KOH electrolyte system.The cycle was more than 5,000 at a current density of 5 A·g-1,and the PMC900 capacitance was still above 92%.Electrochemical performance tests in 3 M H2SO4 show that the stable operating voltage window of PMC900 with the highest phosphorus content(2.34 at%)can be increased from the usual 0-0.9 V to 0-1.6 V,and the energy density of 3.8 Wh·kg-1.It was increased to 11.8 Wh·kg-1.What's more,the capapcitance can maintain more than 90%when it was charged and discharged 5000 times at a current density of 1.0 A·g-1 under the potential window of 0-1.6 V.This shows that the introduction of P can expand the working voltage window of the porous carbon materials in the H2SO4 electrolyte system,thereby increasing the overall energy density of the supercapacitor.The nitrogen and phosphorus co-doped porous carbon materials(NPHCs)with high specific surface area and hierarchical pore structure were prepared by in situ template and NaOH activation using the agricultural waste of lotus seed shell as the carbon source and the nitrogen source,and the sodium phytate as the template precursor and the phosphorus source.The effect of sodium phytate on the structure and electrochemical performance of carbon materials was investigated and the pore formation mechanism was analyzed.The results showed that Na5P3O10 generated from decomposition of sodium phytate reacted with NaOH to convert onto nano-Na2CO3 and nano-Na3PO4 hard templates in situ to form mesopores/macropores,and the activation of residual NaOH can produce a large number of micropores,so the resulting charcoal material has a well-developed hierarchical pore structure.The NPHC2 with a mass ratio of 2:1 of phytate to lotus seed shell exhibited the highest specific surface area(3188 m2·g-1)and pore volume(3.20 cm3·g-1),and was rich in heteroatoms(N:3.31 at%,P:1.66 at%).The specific capacitance of NPHC2 in the 6 M KOH and 3 M H2SO4 aqueous electrolyte are 318 F·g-1 and 414 F·g-1,respectively.And it also has excellent cycle performance and high current rate performance with high specific qualitative capacitances of 241 F·g-1(6 M KOH)and 217 F·g-1(3 M H2SO4)even at high current density of 200 A·g-1.NPHCs are an excellent porous carbon electrode materials,and it has a promising prospect in the application of supercapacitors.