Design-preparation And Supercapacitors Performance Of Porous Carbon-based Electrode Material

Currently,in the process of life and economic development,the destruction of climate and environment caused by the large amount of carbon dioxide and harmful gases generated by the combustion of traditional fossil fuels is becoming increasingly severe.It is urgent for people to intensify research and development of renewable energy.Therefore,the efficient utilization of renewable energy storage devices has become one of the important ways to promote environmental protection and human health.Among the renewable energy storage devices,supercapacitors have emerged as one of the most prospective energy storage devices.Porous carbon materials are widely used as supercapacitors electrode materials due to its excellent properties such as relatively low price,mature preparation process,large surface area,and excellent physical/chemical properties.In practice,because the installation of devices is limited by the space of the entire application scenario,the volumetric performance of electrode materials can better evaluate the supercapacitors than the gravimetric performance.However,the porous carbons have displayed the nature of high porosity and large surface area,but often lead to a low density and significantly reduce the volumetric energy density for the practical application.Based on this,the electrochemical performance and energy storage mechanism of porous carbon with high volumetric performance are systematically designed and constructed through DFT theoretical research,heteroatom doping,pore size regulation and other strategies.The specific research content is mainly divided into the following parts:The first-principles calculations have been performed on the geometric structures and the Na atom adsorption behaviors of the heteroatom-doped graphene.The suitable heteroatom doping configurations are screened out through the calculation and statistical analysis of the formation energy,Bader charge and Na atom adsorption energy of different doping configurations.The pyrrole N,pyridine N,pyridine N and six-membered ring S,pyrrole N and P,pyridine N and P atoms doped graphene show the excellent Na atom adsorption properties.Ab initio molecular dynamics and electronic structure show that there is a synergistic effect between N and S atoms when multiple Na atoms are adsorbed.The ionic and covalent bonds are coexistence between Na atoms and heteroatom-doped graphene,where the interaction between N and Na atoms is strong,while the interaction between the S and P atoms and Na atoms is relatively weak.The N and P atoms co-doped graphene has excellent Na atoms adsorption properties（-2.53 eV）,while maintaining a small Na atom migration barrier（0.75 eV）.Compared with N and S atoms co-doped graphene（-2.36 and 0.93 eV）,The N and P atoms co-doped graphene is beneficial to improve the magnification properties and energy density of graphene electrode.A new strategy to fabricate dense N-doped porous carbon（DNPCs）derived from PANI is prepared by low temperature one step method.It is found that the calcination temperature and PANI doping acid could effectively control the morphology,micropore volume,pore size,defect concentration,N atom doping concentration and type of the N-doped porous carbon,which further affect the volumetric electrochemical performance.The dense N-doped porous carbon electrode（DNPC-500）with phytic acid and 500℃calcination temperature show the excellent supercapacitor volumetric performance.The specific surface area and density of DNPC-500 are 145.39 m²/g and 1.599 g/cm³,respectively.The DNPC-500 performs a high volumetric capacitance of 643.7 F/cm³ at the current density of 0.5 A/g,and the rate retention is 71.8%.The symmetrical device constructed based on the DNPC-500 exhibits a high volumetric energy density of 14.6 Wh/L.A facile approach to synthesize the N and P atoms codoped hollow porous carbons（NPPCs）derived from PANI by utilizing the self-sacrificial template method.The morphology and properties of porous carbon are regulated by adjusting the concentration of crystal inhibitor,ANI,PANI doping acid and pyrolysis temperature,and then affects the supercapacitor performance of porous carbon electrode.It is found that the crystal inhibitor can control the aspect ratio of MnO₂,the concentration of ANI mainly affects the width of PANI,the PANI doping acid could control the porosity and doping atoms of porous carbon,the pyrolysis temperature mainly affects the morphology,porosity and defect concentration of porous carbon,and these factors further affect the volumetric electrochemical performance of porous carbon.The N and P co-doped hollow porous carbon（NPPC-700）is prepared with the concentration of（NH₄）₂SO₄ as 0.0066 mol/L,molar ratio of ANI to MnO₂ as 1:1,phytic acid as PANI doping acid,the pyrolysis temperature of 700℃has the best supercapacitor volumetric performance.The specific surface area and density of NPPC-700 are 142.97 m²/g and 1.46 g/cm³,respectively.The fabricated NPPC-700 electrode demonstrates an outstanding volumetric capacitance of 398.11 F/cm³ at 0.5 A/g,and the rate retention is75.8%.The assembled symmetrical device has a voltage window of 1.4 V and exhibits a volumetric energy density of 20.48 Wh/L.