Preparation Of Polyaniline-based Electrode Materials For High-performance Supercapacitors

Supercapacitors are one of the crucial devices for energy storage applications asthey can provide higher power density than batteries and higher energy density thanconventional dielectric capacitors. The electrode materials are one of key factors thataffect the electrochemical properties of the supercapacitor. Many materials have beeninvestigated as electrode materials for supercapacitors, and the electrode materials aremainly the following three types: carbon-based materials, transition metal oxides andconducting polymers. Among them, polyaniline (PANI) is a kind of typical conductivepolymers, and it has many advantages such as low cost, easy synthesis andenvironmental friendliness, as well as it has high electrical conductivity, goodchemical stability and pseudocapacitor characteristics. So it is generally consideredsuitable for the next generation of supercapacitors. In addition, the N-dopingstructures carbon materials are believed to provide pesudocapacitance contributedfrom the redox faradaic reactions of these electrochemically active functional groups,and the pyrolysis of nitrogen-containing precursor (such as PANI) is preferredbecause it is easier, more cost-effective, and more controllable for the N-dopingcontent.In this paper, we prepared polyaniline-based electrode materials, such aspolyaniline nanotubes, asymmetric supercapacitors is assembled using polyanilinenanotubes as a positive electrode and nitrogen-containing carbon materials areprepared by the carbonization of nanostructured polyaniline. The morphology,structure and electrochemical properties of the materials are characterized in detail.The main research contents and results are as follows:1. Polyaniline (PANI) nanotubes with outstanding electrochemical properties havebeen successfully synthesized via a simple chemical template-free method in thepresence of D-tartaric acid (D-TA) as the dopant, and ammonium persulfate((NH4)2S2O8) as the oxidant. The PANI-(D-TA) nanotubes electrode, with[D-TA]/[aniline] molar ratio of1:1, exhibits larger specific capacitance (as high as625F g-1at1A g-1) and higher capacitance retention (77%of its initial capacitanceafter500cycles) in1M H2SO4aqueous solution. The remarkable electrochemicalcharacteristics of PANI-(D-TA) are mainly attributed to their unique nanotubular structures, which provide a high electrode/electrolyte contact area and short ionsdiffusion path. These novel PANI-(D-TA) nanotubes will be promising electrodematerials for high-performance supercapacitors.2. Asymmetric supercapacitors (ASCs) with high energy density is assembledbased on pseudocapacitance in both electrodes, which is using polyaniline (PANI)nanotubes as a positive electrode and WO3nanorods as a negative electrode in1MH2SO4aqueous electrolyte. The assembled novel PANI//WO3ASCs device with anextended operating voltage window of2.0V in spite of the use of aqueous electrolyteand exhibits excellent performance such as a high specific capacitance of302F g-1ata current density of0.5A g-1, reaching an energy density as high as41.9Wh kg-1at apower density of261W kg-1and good cycling stability. The asymmetricsupercapacitor also exhibits a good electrochemical stability with83%of the initialcapacitance over consecutive2,000cycle numbers. This novel ASCs device isdesirable for applications in supercapacitor.3. Nitrogen-containing carbon nanospheres with a diameter of250nm wereprepared with the direct carbonization method using polyaniline nanospheres as acarbon precursor at different temperatures. Polyaniline nanospheres have beensynthesized via in-situ oxidation polymerization of aniline in the presence of sodiumcarboxymethyl cellulose as a polymerization template. Electrochemical properties ofthe carbonized PANI nanospheres have been studied by cyclic voltammograms andgalvanostatic charge/discharge measurements in6M KOH. The C-PANI-800hasgenerated a high specific capacitance of359F g-1at1A g-1. Furthermore, the specificcapacitance of C-PANI-800can remain290F g-1at high current density of20A g-1. Italso exhibits a good cycling durability with95.9%specific capacitance retained at acurrent density of3A g-1after10,000cycles.