Preparation And Electrochemical Properties Of Polyaniline And Its Composite Electrode Materials

Under the condition of the fossil energy exhausted and the new energy limited,it becomes an urgent task to develop a new environmental-friendly energy storage device with high efficiency.In order to improve the disadvantages of short service life,complex process and unfriendly to environment of fuel cells and secondary cells,supercapacitors have emerged with the joint efforts of many researchers all over the world.Electrode materials play a decisive role in the compose of supercapacitors,which include three may types:carbon materials,conductive polymers and transition metal compounds.Graphene,a typical representative of carbon materials,is widely used in double layer capacitors,with perfect two-dimensional structure,high electrical conductivity,stable chemical properties and large surface area.Polyaniline is an important compose of conductive polymer,which has become a very important electrode material because of cheap,simple synthesis and conductivity.On behalf of transition metal oxide,manganese dioxide has a great attraction as electrode material due to its easy synthesis,non-toxic environmental protection and high theoretical capacitance value,becoming a tipical pseudocapacitive material.Polyaniline is prepared by solution polymerization and three reaction conditions are changed,with the effects to the performance of polyaniline are studied.With different acid doping,on condition of 2 mol/L hydrogen ion concentration,the polyaniline fibers have uniform diameter,regular morphology,less agglomeration,and the conductivity is obviously higher than that of 1mol/L.Among which,the highest conductivity of the sample PANI-2.0 HCl is 9.04 S/cm.For different temperature,polyaniline showed fibrous structure at 5? with a diameter of about 200 nm and more uniform morphology.With the temperature increasing,the agglomeration phenomenon gradually appears and the conductivity of the four samples is also obviously decreased.The highest conductivity of the sample PANI-5 is 8.74 S/cm,while the lowest conductivity of the sample PANI-35 is only 1.93 S/cm,with the decrease rate about 78%.For different initiator ratio,the fibrous structure of polyaniline is more obvious.With the ratio of initiator increasing,the diameter of the fiber is larger and the uniformity becomes worse.The sample PANI-1,3 shows more regular fibers with diameter of about 100 nm.As the ratio of initiator increases,the conductivity of four samples increases first and then decreases.The highest of the sample PANI-1.3 can reach 8.41 S/cm while the lowest conductivity of the sample PANI-1.9 is only 5.56 S/cm.Reduced graphene oxide is synthesized by high temperature oxidize and redox,and polyaniline/reduced graphene oxide composites are prepared,with the morphology,structure and electrochemical properties characterized.The morphology of reduced graphene oxide is lamellar structure with relatively smooth surface,and the overlap of lamellar appears.The CV curves of reduced graphene oxide have no redox peaks,and the GCD curves show the symmetry of charge and discharge,showing typical characteristics of double layer capacitance.The specific capacitance is 229.1 F/g at the scan rate of 5 mV/s and 117.2 F/g at the current density of 0.5 A/g.Its energy density is 14.65 Wh/kg and power density is 229.3 W/kg,respectively,with the specific capacitance retention of 79.2%after 2000 cycles.In the polyaniline/reduced graphene oxide composites,polyaniline is linearly distributed on the graphene lamellae to forme the frame structure.The specific capacitance of polyaniline/reduced graphene oxide composite is 285.4 F/g at the scan rate of 5 mV/s and 147.2 F/g at the current density of 0.5 A/g,while its energy density is 18.4 Wh/kg and power density is 240.1 W/kg,respectively.Compared to reduced graphene oxide,all electrochemical performance index are improved.This is attributed to the combination of double layer capacitance and pseudocapacitance in the composites,which improves the electrochemical properties.Manganese dioxides are successfully synthesized by liquid phase precipitation and polyaniline/manganese dioxide composites are prepared in the suspensions of MnO2.The morphology,functional groups and electrochemical properties are analyzed.Manganese dioxides are prepared with different temperature,showing three different lattice structures of ?-MnO2,?-MnO2 and ?-MnO2.The CV curves of four manganese dioxide samples show a group of redox peaks due to the valence change of manganese elements.The specific capacitance of the sample MnO2-40 is 254.9 F/g at the scan rate of 5 mV/s and 241.6 F/g at the current density of 1 A/g,which are the maximum of the four samples.This is owing to the ?-MnO2 of layered structure,so that the electrolyte cations can get into the interlayers to obtain better electrochemical activity.The FTIR absorption peak and XRD vibration peak of manganese dioxide are retained in the sample of polyaniline/manganese dioxide composite,and the typical characteristics of polyaniline also exist at the same time,with the redox peak of manganese elements appeared in the CV curves.The specific capacitance of the sample PANI/MnO2-40 is 323.7 F/g at the scan rate of 5 mV/s and 291.7 F/g at the current density of 1 A/g,which are the maximum of the four samples and are also higher than the specific capacitance of manganese dioxide.