Fabrication Of Hierarchically Porous Carbon Materials And Their Electrochemical Properties

Hierarchically porous carbon materials have become potential energy storage electrode materials because of its stable physicochemical properties,better electrical conductivity,environmental friendliness,etc.Herein,a series of hierarchical porous carbon materials were successfully synthesized by a template method,and its electrochemical propertie were studied as electrode materials for electrocatalytic oxygen reduction reaction（ORR）,zinc-air battery（ZAB）and supercapacitor（SC）,respectively.The effects of hierarchical porous structure,nitrogen element doping and other carbon nanomaterials modification on their electrochemical properties were systematically studied.Firstiy,N-doped hierarchical porous carbon materials（NHPCs）were successfully synthesized.The as-prepared NHPCs exhibits large pore volume,inter-connected hierarchical porous structure and high content of N doping.Benefiting from the synergistic effect of above advantages,the as-prepared NHPCs presents a half-wave potential 0.883V vs.RHE,which is more positive than Pt/C in ORR test of a 0.1 M KOH electrolyte with a scan speed of 5 m V s^-1 and a speed of 1600 rpm,better initial potential of 1.004 V vs.RHE,and favorable tolerance against methanol.The maximum output power density is up to 25.1m W cm^-2 in ZAB with 6 M KOH electrolyte,and delivers a superior durability of charge and discharge performance at a current density of 10 m A cm^-2.In addition,as the electrod materials of SC,the as-prepared NHPCs release a high specific capacitance of 283.7 F g^-1 at a current density of 1 A g^-1 in 1 M H₂SO₄ electrolyte.The assembled symmetrical supercapacitor（SSC）have a gravimetric capacitance of 81.6 F g^-1 at current density of1 A g^-1 in 1 M H₂SO₄ electrolyte,and outstanding capacitance retention of 99.3%after12,000 cycles at current density of 6.7 A g^-1.The energy density of SSC is 11.3 Wh kg^-1at the power density of 502 W kg^-1,and still retains at 7.7 Wh kg^-1 even at a high power density of 8691 W kg^-1.The results showed that the as-prepared NHPCs exhibited excellent electrochemical properties.In order to further improve the capacitive properties of NHPCs,graphene（GO）,carbon dot（CD）and carbon nanotube（CNT）modified N-doped hierarchical porous carbons（GO/NHPCs,CD/NHPCs and CNT/NHPCs）were synthesized respectively.The effects of modification of GO,CD and CNT on the structure and capacitance of NHPCs were systematically studied.The results show that the as-prepared hierarchical porous carbon composities have large pore volume,interconnected hierarchical porous structures and high specific surface area.Forthermore,the presence of GO,CD and CNT can effectively improve the N doped in these composites,and further optimize their pore structure.When used as a SC electrode material,CD is more beneficial to the improvement of the capacitor performance than that of GO and CNT.The gravimetric capacitance of CD/NHPC-10 is 343.6 F g^-1 at current density of 1 A g^-1 in 1 M H₂SO₄ electrolyte,which is higher than 308.1 F g^-1for GO/NHPC-15 and 273.9 F g^-1 for CNT/NHPC-10.All solid-state supercapacitor of GO/NHPC-SSC,CD/NHPC-SSC,CNT/NHPC-SSC,NHPC-SSC are assembled by using the as-prepared GO/NHPC-15,CD/NHPC-10,CNT/NHPC-10,NHPC electrodes and H₂SO₄/PVA gel electrolyte,respectively.The gravimetric capacitance and volumetric capacitance of CD/NHPC-SSCs are 77.6 F g^-1 and 2.33 F cm^-3 at current density of 1 A g^-1,which is superior to GO/NHPC-SSC(76.3 F g^-1 and 2.29 F cm^-3),CNT/NHPC-SSC(67.7 F g^-1 and 2.03 F cm^-3),NHPC-SSC(66.3 F g^-1 and 1.99F cm^-3).Furthermore,the energy density of CD/NHPC-SSC is 10.3 Wh kg^-1at the power density of 488.8 W kg^-1,which is superior to GO/NHPC-SSC,CD/NHPC-SSC,CNT/NHPC-SSC and NHPC-SSSC.In addition,the device deliveres a good cycle stability with the capacitance retention up to 85.7%after 10000 cycles at current density of 10 m A cm^-2.The bending test results of the device illustrates its good mechanical stability.