Structural Design,Regulation And Structure-Property Relationship Of PANI-Based Composite Electrode Materials For High Performance Supercapacitors

With the global warming,ozone depletion,haze and other environmental problems are increasing and fossil energy consumption problems become increasingly serious,the research and application of novel and efficient energy storage and conversion devices are needed.Supercapacitors?SC?,also called electrochemical capacitors,has a higher power density compared with batteries and a higher energy density compared with conventional capacitors.SC has a long cycle life,high reliability,high charge and discharge speed,environment-friendly and other advantages.In order to maximize the advantages of supercapacitors,electrolyte and electrode materials have attracted increasing attention due to they are important part of the device.The electrode materials of SC can be divided into electric double layer capacitor materials?carbon materials?and pseudo-capacitance materials?transition metal oxides and conductive polymer?.Polyaniline?PANI?has been considered as one of the most useful conducting polymers for electrode materials due to its ease of synthesis,high doping rate,high conductivity,high theoretical specific capacitance and environmental friendliness.Unfortunately,the important factors that restrict the development of PANI are:?i?poor cycle life caused by volume swelling and shrinking during the doping and dedoping process,?ii?relatively low specific capacitance compared with theoretical value due to suffer from insufficient exposure to the electrolyte.In this paper,the problem of poor cycle stability and low specific capacitance of PANI when used as electrode materials for supercapacitors are improved through the unique structural design and preparation of composite materials.Specific studies are as follows:1.In this paper,a novel urchin-like mesoporous TiO₂ spheres?UMTS?have been synthesized using a simple one-step hydrothermal reaction and used as a supporting material,and subquently in situ polymerization of PANI on the surface of UMTS by using APTES as coupling reagent to obtain UMTS/PANI nanocomposite.The results of SEM and XRD test indicates that the PANI is assembled around the UMTS and there is a strong interaction between the PANI and UMTS.The high specific surface area of the support material has not only increased the exposure area of PANI to the electrolyte,but also improve the structural stability of PANI by using APTES.Electrochemical tests further show that the composites have excellent electrochemical performance due to the use of supporting material with high specific surface area and the unique structural design.As a electrode material for supercapacitors,PANI/UMTS shows a great cycle stability and good electrochemical performance.The nanocomposite exhibits a high specific capacitance of 422 F g^-1 at the current density of 0.7 A g^-1 and excellent capacitance retention of almost 100%after 500 cycles at a current density of 7 A g^-1.2.In order to overcome the problem of poor conductivity of UMTS with high specific surface area,the core of the composites was further improved on the basis of the above research,the titanium dioxide nanospheres were nitrided under the atmosphere of ammonia.The result of XRD shows that the titanium dioxide nanospheres have been completely nitrided to titanium nitride nanospheres and the elemental mapping analysis shows that the N-elements of the nanospheres after nitriding were evenly distributed.SEM,TEM and BET analysis show that the nanospheres after nitriding are hierarchical porous titanium nitride spheres?HPTNS?.HPTNS are hollow structure and the surface is composed of many small pieces,while still having a high specific surface area.However,compared with UMTS,HPTNS have a wide range of pore size distribution,good conductivity and other advantages.Subsequently,PANI are assembled on the surface of HPTNS by using silane coupling agent and obtain the HPTNS/PANI nanocomposite.The electrochemical test confirms that the material has good electrochemical performance,the specific capacitance of nanocomposite reaches 530.8 F g^-1 at a current density of 0.5 A g^-1.3.Although the use of silane coupling agent in the study 1 improves the cycling stability of the material,the silane coupling agent has poor electrical conductivity.In this study,volume swelling and shrinking of PAN during the process of charging and discharging were restricted to improve the cycling stability by using unique nanostructure design,and the electrochemical performance of the material was also improved.In the study,the PANI was firstly in situ polymerized on the surface of the UMTS without the use of a silane coupling agent,And then positively charged PANI/UMTS nanospheres are inserted into the negatively charged graphene oxide?GO?sheets through electrostatic interactions under ultrasound conditions.Finally,GO is reduced as RGO to obtain the RGO/PANI/UMTS ternary composite.The ternary composite displays pretty good specific capacitance and excellent cycling stability,is a promising electrode material for electrochemical energy storage devices.4.The use of RGO in the study 3 has a unique advantage,but the synthesis process is complex.In this study,RGO will be replaced by graphene-like Mo S₂ during the preparation process.Herein,we report a simple strategy that enlarge the exposure area of PANI to the electrolyte by synthesizing of macroporous polyaniline nanorods?MPN?using solid silica nanospheres?SiO₂?as templates,and then few-layer Mo S₂ nanosheets are coated on the surface of MPN via the reduction of ammonium tetrathiomolybdate to obtain the MPN@Mo S₂ nanaocomposite.As a result,the obtained MPN@Mo S₂nanocomposite exhibits an outstanding capacitive performance of 602.9 F g^-1 at the current density of 0.5 A g^-1 and the composite presents excellent cycle stability with13.3%of capacity loss at 10 A g^-1 after 2000 cycles.All results demonstrate that MPN@Mo S₂ is a promising electrode material for high performance supercapacitors.5.On the basis of the above work,this study used a novel hierarchical porous TiO₂microspheres?HPTM?with high specific surface area as the supporting material and further in situ polymerization of PANI on the surface of HPTM by using APTES as coupling reagent.Finally,polyaniline/HF partially etched-hierarchical porous TiO₂microspheres?PANI/F-HPTM?composite was prepared through a partial etching method using HF as the etchant.The unique partial etching strategy not only improve the electrochemical performance of the material,but also the advantages of the supporting material with unique morphology are achieved and the structure of polyaniline is reinforced.The electrochemical measurement indicates that the prepared PANI/F-HPTM composite displays pretty good specific capacitance and excellent cycling stability.