Design, Preparation And Capacitance Properties Of Polyaniline Based Electrode Materials

Supercapacitor has drawn considerable attentions because of its high specific power density,long cycle life and low cost.The capacitive performance of the supercapacitor is influenced by the electrode materials,electrolytes,and the assembled technique.Research 'results indicate that the electrode materials have a mainly influence for the performance of supercapacitor.Polyaniline?PANI?is one of the widely researched electrode materials because of its large theoretical specific capacitance,good electric conductivity,simple synthesis and low cost.However,its low practical capacitance,poor rate performance and cycling stability seriously limit PANI application as promising electrode materials.Many methods have been used to effectively improve these drawbacks of PANI electrode materials,such as optimizing the nanostructure and morphology of PANI electrode materials,preparing PANI-based composite materials and applying redox electrolytes.In this thesis,PANI-based electrode materials with different morphologies have been designed and prepared by different methods.The composition,structure,and morphology of as-prepared PANI-based materials are characterized by FTIR,Raman spectroscopy,X-ray diffraction?XRD?,field emission scanning electron microscopy?FESEM?and transition electron microscopy?TEM?.The capacitive properties of PANI-based electrode materials for supercapacitor have been systematically investigated.The effect of the morphology,composition,and structure on the capacitive properties has also been investigated.Moreover,redox electrolytes are applied to symmetric supercapacitor assembled by flower-like PANI in order to investigate their influence on supercapacitor capacitive behaviors.The main contents of this thesis are as follows:By using manganese dioxides?a-MnO₂?with different morphologies as templates as well as oxidants,four nanostructured PANI electrode materials with different morphologies including nanofibers,nanoflowers,nanorods,and nanotubes have been prepared by an adsorption-template technique in acidic condition.The research results indicate that the formation of PANI with different morphologies is manily influenced by the adsorption-template process and the concentration of H₂SO₄ aqueous solution.The obtained PANI electrode materials with different morphologies show not only better dispersity,but also better uniformity in size.The electrochemical measurements in three-electrode system show that their capacitive properties are highly dependent on their morphology.The PANI nanotube electrode material exhibits the highest specific capacitance and the best rate performance among the four PANI morphologies.The PANI nanotube electrode shows the specific capacitance of 661 F g^-1 at a current density of 1 A g^-1,and the rate performance of 88%when the current density increases from 1 to 10 A g^-1.The hollow interior structure can fully take advantage of faradic pseudocapacitance and favors fast ionic transportation at high current density inside the nano-scale electrode material.The adsorption-template technique may be readily extended to prepare other conducting polymers with good capacitive properties.By using tubular molybdenum disulfide?MoS₂?assembled by MoS₂ nanosheets as growing substrate,tubular MoS₂/PANI electrode materials with different amounts of PANI have been prepared in situ oxidative polymerization of aniline monomers in acidic condition.The PANI nanowire arrays with a diameter of 10?20 nm can be controllably grown on both the external and internal surface of tubular MoS₂ when the mass of PANI is 60%?MoS₂/PANI-60?.The electrochemical measurements in three-electrode system show that MoS₂/PANI-60 electrode not only has a high specific capacitance of 552 F g^-1 at a current density of 0.5 A g^-1,but also gives excellent rate capability of 82%from 0.5 to 30 A g^-1.The specific capacitance,rate capability,and cycling stability of MoS₂/PANI-60 are superior to PANI,which can be mainly attributed to the special tubular architecture and the synergistic effect between MoS₂ substrate and PANI nanowire arrays.Moreover,the tubular MoS₂/PANI-60 symmetric supercapacitor also exhibits the excellent rate performance and good cycling stability.The specific capacitance based on the total mass of the two electrodes is 124 F g^-1 at a current density of 1 A g^-1 and 79%of its initial capacitance is remained after 6000 cycles.The tubular structure provides a favorable method for improving the capacitance retention and cycling stability of PANI electrode.By using RGO film obtained by self-assembled filtration technique as flexible substrate,polyaniline-poly?hydroquinone?/graphene?PANI-PHQ/RGO?film electrode materials with different RGO amounts have been prepared in situ chemical oxidative polymerization method.The electrochemical measurements in three-electrode system exhibit that the PANI-PHQ/RGO-61?the mass of RGO is 61%?film electrode has a specific capacitance of 356 F g^-1 at a current density of 0.5 A g^-1,and also gives a high capacitance retention of 83% from 0.5 to 30 A g^-1.After 1000 cycles of the galvanostatic charge-discharge,PANI-PHQ/RGO-61 film electrode presents an excellent cycling stability with capacitance retention of 94%of and an outstanding Columbic efficiency of 99%.The existence of redox active PHQ in PANI-PHQ/RGO-61 film electrode makes it has better cycling stability than PANI?60%? and PANI/RGO-60?74%?electrodes.Moreover,the electrochemical reversibility and rate performance of PANI-PHQ/RGO-61 film electrode are also superior to those of PANI and PANI/RGO₆0 electrodes.This research provides a novel method for preparing film electrodes with excellent capacitive property.A symmetric supercapacitor has been assembled by using flower-like PANI as electrode material,which is prepared by a simple chemical oxidative polymerization method.The Fe³⁺/Fe²⁺ active redox couple is added into H₂SO₄ electrolyte and the obtained redox electrolyte is expected to improve the capacitive performance of the supercapacitor.The Fe³⁺/Fe²⁺ additive is not only electrochemical active component,but also shows the electrolyte feature.The capacitive behavior of the flower-like PANI symmetric supercapacitor in redox electrolyte with different concentration of Fe³⁺/Fe²⁺has been systematically tested,and the electrochemical test results show that the specific capacitance of supercapacitor is highest when the concentration of Fe³⁺/Fe²⁺active redox couple is 0.8 M.The specific capacitance of flower-like PANI symmetric supercapacitor in 1 M H₂SO₄+0.8 M Fe³⁺/Fe²⁺ active redox electrolyte is three times larger than that in 1 M H₂SO₄ electrolyte,and the energy density is 22.1 Wh kg^-1 when the power density is 774 W kg^-1.In addition,flower-like PANI symmetric supercapacitor shows outstanding cycling stability,and the specific capacitance remains 93%of its initial value at a current density of 5 A g^-1 after 10000 cycles,also its structure and morphology nearly maintain after the cycling stability test.Meanwhile,the redox electrolyte can also improve the capacitive performance of RGO double layer electrode based symmetric supercapacitor effectively.The redox electrolyte supports a favorable method to improve the capacitive performance of supercapacitors.