Controlled Synthesis And Electrochemical Performance Of Heteroatom-doped Hierar-chical Porous Carbon Materials

As a promising energy storage device,supercapacitors have the advantages including long service life and high charge discharge efficiency.Carbon materials can be widely used as electrode materials for supercapacitors due to their advantages such as wide source,good conductivity,high stability,and good structure controllability.Compared with commercial activated carbon,heteroatom-doped hierarchical porous carbon materials can show higher specific capacity and rate performance,which has become the focus of current research.At present,heteroatom-doped hierarchical porous carbon materials are mainly prepared by combined soft-hard templating or combined template-activation method.Extra template removal or activation steps make the preparation process complicated,and may also cause the loss of heteroatoms.Therefore,how to construct a hierarchical porous carbon material with a high content of heteroatom doping level,high specific capacity and high rate performance by a simple method,has become one of the key challenges in this field.In this paper,a"self-sacrificial Fe₃O₄ clusters induced polymerization method"is proposed to construct porous functional conductive polymer microspheres in one step,followed by direct carbonization to construct heteroatom-doped hierarchical porous carbon materials.Hydrochloric acid gradually dissolves polyacrylic acid-modified Fe₃O₄ nanoclusters as self-sacrificing templates,and iron ions could be released from the surface of magnetite clusters.Subsequently,iron ions?III?could oxidize in-situ the conductive polymer monomer as pyrrole or thiophene to form porous conductive polymer or copolymer microspheres,followed by direct carbonization to obtain nitrogen,oxygen co-doped hierarchical porous carbon microspheres and nitrogen,sulfur,oxygen multi-doped hierarchical porous carbon microspheres,respectively.Transmission electron microscopy?TEM?,X-ray diffraction?XRD?,Raman spectroscopy?Raman?,isothermal nitrogen absorption and desorption,X-ray photoelectron spectroscopy?XPS?and other test methods were used to characterize the microstructure,doped elements,specific surface area,pore structure and other parameters of these two carbon materials.For both carbon materials,heteroatoms are uniformly doped in the carbon material structure,and exhibit a hierarchical porous structure including micropores,mesopores,and macropores.Using sulfuric acid as the electrolyte,and under the three-electrode system,these two carbon materials show the characteristics of both pseudo-capacitance and electric double layer capacitance,and exhibit a high mass ratio capacitance.The specific surface area of N,O co-doped carbon material reaches 605 m²/g,and the capacitance value can reach 381.2 F/g at a current density of 10 A/g.The N,S,O multi-doped carbon material has a specific surface area of 218 m²/g,and its capacitance value can reach 405.2 F/g at a current density of 10A/g.Both materials show good rate performance and extremely high electrochemical stability,due to the high content of heteroatom doping and hierarchical porous structure characteristics of these two carbon materials.The heteroatom doping effectively improves its pseudo-capacitance,and the hierarchical porous structure effectively enhances the ion diffusion rate to reduce charge transfer resistance,thereby increasing its rate capability.The"self-sacrificing Fe₃O₄ clusters induced polymerization method"proposed in this paper achieves template removal and polymerization in one step,greatly simplifying the synthesis process of heteroatom-doped hierarchical porous carbon materials,which provides some reference for the development of new heteroatom-doped porous carbon materials.