Study On Preparation And Electrochemical Performance Of Multi-Heteroatoms-doped Hierarchical Porous Network Materials For Supercapacitor

The world is experiencing an incessant consumption of fossil fuels and an intensifying greenhouse effect,indicating the need for an environmentally friendly and clean energy.Solar energy,wind energy,and other clean energies are critically affected by the environment.Therefore,an energy storage device must be established for clean energy.Given them high power density and long cycle life,supercapacitors have been extensively studied.Carbon-based materials are considered one of the most ideal electrode materials for supercapacitors because of their tremendous specific surface area,remarkable chemical and electrochemical stabilities,excellent conductivity,and abundant electrocatalytic active sites for various redox reactions.However,the pore structure,types and contents of heteroatoms introduced into electrode materials can not be precisely regulated.Therefore,in this study,the target heteroatoms?P,F?are introduced by means of simple and efficient host–guest interaction,which greatly improves the electrochemical properties of the materials.In addition,benefiting from the molecular engineering strategy,N and O heteroatoms are introduced into the porous network through covalent bonds.And then,the contents of heteroatoms,pore structure and other microscopic factors could modified via changing the polymerization temperature.Finally,the polymerization process is optimized to explore the relationships between the microscopic structure and electrochemical performance.The specific contents of this paper are as follows:?1?Benefiting from the molecular engineering strategy,the N,O-containing monomer 4,4?-?4-oxophthalazine-1,3?4 H?-diyl?dibenzonitrile?OPDN?was designed and synthesized.we obtained multi-heteroatom carbon frameworks?MHCFs@600?with a uniform distribution of oxygen and nitrogen atoms by ionothermal synthesis polymerization.Then,basing on the measurement of the pore size distribution,?CH₃CH₂CH₂CH₂?₄N⁺?PF₆?^-was introduced to the MHCFs@600 by simple and high-efficiency host–guest interaction to obtain an electrode material?f-MHCFs@600?rich in N,O,P,and F.SEM mapping images of f-MHCFs@600indicate the homogeneous distribution of N,O,P,and F elements.XPS survey spectrum of f-MHCFs@600 indicates that the N,O,P and F contents are 6.83 at.%,6.22 at.%,2.25 at.%,7.23 at.%,respectively.Electrochemical performance tests show that the introduction of P and F heteroatoms can not only increase the voltage window of the aqueous electrolyte?from 1.0 V to 1.4 V?,but also reduce the impedance of MHCFs@600.In a three-electrode test system?1M H₂SO₄?,the specific capacitance of f-MHCFs@600 was 244.8 F g^-1(at 0.1 A g^-1)that was maintained at 164.3 F g^-1(at 10 A g^-1),indicating a high capacitance retention of 67%.The cycle performance was estimated at a high current density of 10 A g^-1.The specific capacitance maintained 98.5%of the premier charge and discharge after 10000 cycles.Two f-MHCFs@600and MHCFs@600 electrodes were symmetrically assembled with a 1 M H₂SO₄ electrolyte in Swagelok cells.Moreover,the introduction of phosphorus and fluorine increased the voltage window,resulting in energy density from 3.78 Wh kg^-1 to 8.1 Wh kg^-11 at 1 A g^-1 and the power density from 1400 W kg^-1 to 3500 W kg^-1 at 10 A g^-1,and the retention of specific capacitance maintained about 94.5%after 20000 cycles at 10 A g^-1.?2?A new monomer 4,4'-?1,3,5,7-tetraoxo-5,7-dihydropyrrolo[3,4-f]isoindole-2,6?1H,3H?-diyl?dibenzonitrile?TIDN?,containing imide structure,was designed and synthesized,and the monomer was characterized by infrared,TGA and elemental analysis.The Polymer-TIDN?p-TIDN?were prepared by ion thermal method at different polymerization temperatures,polymerized at 550°C,600°C,650°C and 700°C,respectively,to obtain p-TIDN@550,p-TIDN@600,p-TIDN@650,p-TIDN@700.SEM,Raman and X-ray diffraction?XRD?images of p-TIDN indicates a decrease in the microstructure ordering.TEM images of p-TIDN show that p-TIDN are porous materials.The Brunauer-Emmett-Teller?BET?surface area of p-TIDN@550,p-TIDN@600,p-TIDN@650 and p-TIDN@700 are 1292.30 m² g^-1,1374.19 m²g^-1,1409.73 m² g^-1 and 1526.83 m² g^-1,respectively.The XPS analysis reveals that the contents of N decrease with the elevated polymerization temperature.The atomic percentages of nitrogen in p-TIDN@550 and p-TIDN@700 are 8.55 at.%and 5.95 at.%,respectively.In a three-electrode test system?1 M H₂SO₄?,the specific capacitance of p-TIDN@600 was 231.35F g^-1(at 0.1 A g^-1)that was maintained at 143.76 F g^-1(at 10 A g^-1),indicating a high capacitance retention of 62%.The cycle performance was estimated at a high current density of 10 A g^-1.The specific capacitance maintained 112%of the premier charge and discharge after 30000cycles.In order to further explore the effect of nitrogen-and oxygen-containing functional groups on its electrochemical performance in supercapacitors,the relationship between the specific capacity of p-TIDN@550,p-TIDN@600,p-TIDN@650 and p-TIDN@700 and the N and O heteroatom contents was analyzed in detail.These results confirm that the specific capacities increased with the increase of N and O indices in p-TIDN@550,p-TIDN@600,p-TIDN@650 and p-TIDN@700.It can be verified that pyrrolic nitrogen,pyridinic nitrogen and quinone oxygen are conducive to the pseudocapacitance by increased the specific capacities with the increase of the combination of I-N5,I-N6 and I-OI.In a two-electrode system?TEABF4/AN electrolyte?,p-TIDN@700 has better capacitance than p-TIDN@550,p-TIDN@600 and p-TIDN@650.The energy density of p-TIDN@700 was 24.23 Wh kg^-1 in TEABF4/AN electrolyte,and the retention of specific capacitance maintained about 90%after20000 cycles(at 10 A g^-1).