The Application Of Polyaniline Prepared By Microemulsion Method In Supercapacitor

As a new energy storage device, the performance of the supercapacitors isbetween the typical dielectric capacitors and the rechargeable batteries. Theperformances of supercapacitors are mainly determined by electrode materials whichinclude carbon materials, metal oxides and conducting polymers and so on.Polyaniline （PANI） has attracted great attention due to the unique performances in thefamily of conducting polymer. In this paper, we have synthesized thenano-polyaniline by the way of emulsion method and microemulsion method. Also,we prepared the PANI/AC electrode to research the electrochemical behaviours. Themorphologies, structures of the materials were characterized by scanning electronmicroscopy （SEM） and transmission electron microscopy （TEM）. And theelectrochemical characterisations of these materials were carried out by means ofcyclic voltammetry （CV）; galvanostatic charge-discharge experiments andelectrochemical impedance spectroscopy （EIS）. The main contents of this paper are asfollows:（1） The preparation of AC electrode and electrochemical performancesThe electrochemical performances of the AC electrode were tested in the H₂SO₄solution system. The SEM results indicated that the nanoscale carbon black isuniformly dispersed in the surrounding of the activated carbon to form a conductivenetwork. The CV, galvanostatic charge-discharge and EIS experiments demonstratedthat the AC electrode has the character of double electric layer capacitor and showed agood reversibility. The specific capacitance （SC） of the AC electrode was171.2F·g^-1at current density of5mA·cm^-2. The SC can retain95%of the initial capacity after1000th cycles. The symmetric capacitor showed a specific energy of8.6Wh·kg^-1at aspecific power of144.9W·kg^-1at the current density of2mA·cm^-2and a window of 1.0V. These results indicated that the performances of the AC electrode still need tobe further improved.（2） The capacitance performances of PANI prepared by microemulsion methodThe nano-polyaniline was synthesized by microemulsion method which SDBS asemulsifier, HCl as doping agent and BA as assistant emulsifier. The electrochemicalperformances of the PANI/AC electrode were tested in the H₂SO₄solution system.SEM showed that the agglomeration of PANI was serious, TEM showed that theprepared PANI was hollow spherical and the diameter is ca.30-40nm. Thegalvanostatic charge-discharge test indicated that the charge-discharge still can beproceed normally after the voltage upper limit increased to1.0V, the SC alsoincreased greatly. After the ball milling treatment of the PANI, the electrochemicalperformances of the PANI/AC electrode was improved. Compared to the ACelectrode, the addition of the nano-polyaniline significantly improved theelectrochemical performances of the PANI/AC electrode. The SC of the PANI/ACelectrode was610.3F·g^-1at current density of5mA·cm^-2. The SC can retain71%ofthe initial capacity after1000th cycles. The asymmetric capacitor showed a specificenergy of25.0Wh·kg^-1at a specific power of204.1W·kg^-1at the current density of2mA·cm^-2and a window of1.0V. So, the performances of the PANI/AC electrodewere improved.（3） The capacitance performances of PANI prepared by emulsion method andmicroemulsion methodThe nano-polyaniline were synthesized by emulsion method which SDS asemulsifier, HCl as doping agent and by microemulsion method which BA as assistantemulsifier. The electrochemical performances of the PANI/AC electrode were testedin the H₂SO₄solution system. TEM showed that the diameter of PANI prepared bymicroemulsion method was smaller and the distribution was more uniform. Also, theelectrochemical performances of the PANI/AC electrode were more excellent whichwere demonstrated by CV, galvanostatic charge-discharge and EIS tests. The SC ofthe electrode was584.4F·g^-1at current density of5mA·cm^-2which the contributionpercentage of capacitance of the nano-polyaniline morphology was50.7%, higher than the26.0%which was provided by the faradaic reaction. This was the first time tocalculate the contribution percentage by graphic method. This indicated that thenano-polyaniline morphology can greatly improve the SC. The SC can retain73%ofthe initial capacity after300th cycles, then the rate of decay became slowly, thedegradation was only7%1000th cycles later compared to the300th cycles due to thecontribution of nano-polyaniline morphology. The asymmetric capacitor showed aspecific energy of29.0Wh·kg^-1at a specific power of243.4W·kg^-1at the currentdensity of2mA·cm^-2and a window of1.0V which were higher than that of thesymmetric capacitor.