Novel Synthesis And Electrochemical Capacitive Behavior Of PANI,MnO₂ And Porous Carbon Materials For Supercapacitor

Efficient energy production and storage in an eco-friendly and sustainable way has become a global objective.A variety of energy storage technologies have been developed to meet this challenge,including mechanical,physical,thermal,chemical and electrochemical energy storage systems.In the various energy-storage elements,supercapacitors?called electrochemical capacitor,SCs?are the new generation promising power source,and because of its medium energy density,high power density and long cycle life,in comparison with conventional capacitors and batteries,applied for the high power supplies,electric and hybrid vehicles,and portable electronics.According to energy storage mechanisms,supercapacitor can be classified as two types: electrical double-layer capacitor?EDLC,fast adsorption and desorption of electrolyte ions?and pseudocapacitors?reversible surface Faradic redox reactions?.A typical supercapacitor can be composed of two electrodes,electrolyte,and a separator between two electrodes,in which the electrode materials?act as main energy storage components?determine the whole supercapacitor performance.Nowadays,there are numerous electrode materials used SCs,such as conducting polymers?PANI,PPY?,metal oxides?MnO₂,Ni O,Co O?and carbon materials?porous carbon,CNTs,graphene?.Among them,PANI,MnO₂ and porous carbon due to low cost,environmentally benign nature,abundant resource and high theoretical specific capacitance?for the first two?,have attracted widely attention in the SCs fields.However,for the PANI and MnO₂ based electrode materials,their practical specific capacitance and cycling performance are still improved.Traditional porous carbon materials were generally prepared from coal,petroleum or their derived products through a series of activation processes.Moreover,as-obtained porous carbon exhibits low specific capacitance,which has become the major obstacle limiting its practical applications.Hence,in this study,according to their existing problems,we have used different synthesis methods to prepared novel hybrid nanomaterials,which possess better capacitive behaviors.The main work is the following:1.A simple and effective route to improve the cycling stability of 1D PANI-based electrode materials by in situ chemical polymerization of aniline on AB/MnO₂ nanotubes as the sacrificial template has been reported.The obtained PANI-AB hybrid nanocomposites with desired 1D hollowed branched structure can increase the effective utilization of active materials throughout the whole electrode matrix and reduced the effective diffusion distance of protons and electrons,leading to excellent cycle durability as well electrochemical performance.The hybrid nanocomposites can exhibit good long-term cycling stability and 86 % of the capacitance can be retained after 1000 cycles by CV test at a scan rate of 50 m V s-1 compared to that of pure PANI-based supercapacitors.Furthermore,the PANI-5%AB hollowed hybrids also exhibit much better electrochemical performance(520 Fg^-1 at 1 Ag^-1)than that of pure PANI pseudocapacitors(271 Fg^-1 at 1 Ag^-1).The as-prepared full cells based on the hybrid structures can be further demonstrated that the PANI-5%AB based electrodes can have promising performance with high power density of 1361 W kg-1 and energy density of 17.8 W h kg-1 at current density of 2 Ag^-1,even 6.32 k W kg-1 and 14.1 W h kg-1 at high current density of 10 Ag^-1.2.The developed capacitance performance and improved long-term cycling stability of MnO₂-based electrodes were obtained through designing MnO₂-Ni?OH?₂ three dimensional?3D?porous hierarchical hybrid nanocomposites?MN-NF/AB?grown on the nickel foam by the aid of conductive adhesive consisting of PVDF-acetylene black?AB?seed layer via a one-step scalable hydrothermal route.The unique 3D ridge-like nanostructures with the features of porous,interconnected active nanosheets and vertically growing on the 3D nickel foam exhibit a high areal capacity(4.86 C cm^-2)and areal capacitance(10.15 F cm^-2)at 4 m A cm^-2 in a three-electrode system,which can effectively eliminate the volume expansion-induced pulverization phenomenon for MnO₂-based electrode materials,resulting in enhanced cycling stability.Furthermore,the assembled product-soft package of asymmetric supercapacitors?MN-NF/AB // active carbon?can have excellent energy storage capacity(3.62 m W h cm^-3 at 11 m W cm^-3)and a long-term cycling stability(86 % of capacitance retention at 50 m A cm^-2 after 10000 cycles).3.We have used a facile one-step and low-cost method to prepare the nitrogen-doped interconnected porous carbon with abundant pore structure by carbonization corn stalk core as an abundant agricultural waste in the NH3+N2 atmosphere,and used KOH as the activating agent.The interconnected porous structure exhibits two narrow pore size distribution,high specific surface area?2155 m2 g-1?,and heteroatom doping?N: 3.96 At%,O: 5.61 At%?,which would promise large reaction interface between electrolyte and electrode,facile ion diffusion and fast electron transport.Hence,the PSC2-700 electrode exhibits a high specific capacitance of 381 Fg^-1 at current density of 0.2 Ag^-1 in 6 M KOH testing in two-electrodes system,and high-rate performance with 82 % capacitance retention at 0.2-80 Ag^-1,superior electrochemical stability with capacitance retention up to 97.6 % after 50000 cycles.Moreover,the assembled product-soft package PSC2-700 SC in the organic electrolyte Me Et3NBF4 showed an improved energy density of 47.5 W h kg^-1.In conclusion,we have used low-cost,facile and environmentally friendly methods to successfully prepare the PANI-AB,MnO₂-Ni?OH?₂ and porous corn stalk core carbon electrode materials.And these materials exhibit an enhanced capacitive performance.In addition,these low-cost materials are able to be applied in the SCs industrial production.