Preparation、Modification And Electrochemical Capacitive Characteristic Of Polyaniline Nanofiber For Supercapacitor

As a kind of new energy storage device combining advantages of the high specific power of dielectric capacitors and the high specific energy of rechargeable batteries, supercapacitor has drawn great attention of academic and industrial circles. Conductive polyaniline (PANI) has been regarded as one of the most potential supercapacitor electrode materials, due to its desirable chemical stability, good conductivity and high faradic pseudo capacitance, as well as the advantages of low cost, facile synthesis and good environmental stability. Especially one-dimensional nano-structure PANI material with high specific surface area, high long-diameter ratio, high porosity and excellent electrical properties, has great research value in electrode field.In this paper, PANI nanofiber material was prepared by selecting convenient and easy polymerization methods on the base of review of plentiful literatures. The polymerization conditions were investigated and optimized systematically, thus the PANI appearance can be controlled; the electrochemical capacitance behaviors of PANI with different appearances were studied in H2SO4aqueous solution; several structure modification techniques were studied and the capacitance behaviors of modified PANI were investigated; The capacitive behaviors of PANI doped with different metal salts were studied, then the proper metal type and doping method were confirmed; Finally, on the base of above research, modified and metal doped PANI and activated carbon composites were prepared by in-situ polymerization, meanwhile their capacitance behaviors were investigated in aqueous or organic solution. The main research results and conclusions are as follows:(1) Chemical adding, rapid mixing and interfacial polymerization were used to prepare PANI nanofiber. Through strictly control and optimizing polymerization conditions, polyaniline nanofiber with uniform size and good morphology can be prepared. The fiber’s average diameter is about50～100nm and length ranges from500nm to several micrometers. Chemical adding and rapid mixing polymerization are promising in industrialization because the advantages of easy operation, low cost and high product efficiency.(2) In H2SO4aqueous solution, polyaniline nanofiber exhibits higher specific capacitance (at the current density of0.1A·g-1, long and short polyaniline nanofiber shows the specific capacitance of404F·g-1and436F·g-1respectively, and granular polyaniline shows the specific capacitance of392F·g-1). Compared with granular polyaniline, long polyaniline nanofiber exhibits better power characteristic and cycle performance (electrode capacitance reduces by9.7%when current density increased from0.1A·g-1to0.5A·g-1and degradation of capacitance is about17.5%after1000cycles).(3) The structure of polyaniline were modified by doping with macromolecule organic acid, copolymerization and substitution methods. The polyaniline doped by dodecyl benzenesulfonic acid (DBSA) and Camphorsulfonic acid (CSA) show similar specific capacitance but cycle properties are deteriorated compared with that doped by HC1(PH). Aniline-m-toluidine copolymer (PAMD) exhibits the similar conductivity and capacitance behaviors as PH, and performances better in cycle stability (at the current density of0.1A·g-1, the specific capacitance of PAMD is381F·g-1, and degradation of capacitance is about15.8%after1000cycles), which demonstrates that introducing methyl group to polyaniline molecule can improve the cycle stability to some extent. A new N-alkylation of polyaniline materials were prepared by treating the emeraldine base polyaniline directly with various alkyl halides and the acquired polyaniline doped with1-Bromobutane (C4H9Br) exhibits good capacitance behaviors (at the current density of0.1A·g-1the specific capacitance is408F·g-1and degradation of capacitance is about20.1%after1000cycles), which proves it can be used as electrode material for supercapacitor.(4) Metal salts doped polyaniline nanofiber (PLi\PZn\PMn\PFe) were obtained by using different metal salts as dopant, and the results show that LiCl、ZnCl2、and MnCl2doping are pseudo-protonation but FeCl3doping is pseudo-protonation with redox reaction. In H2SO4aqueous solution, PZn exhibits the best capacitance behaviors (at the current density of0.1A·g-1, the specific capacitances of PZn is340F·g-1and degradation of capacitance is about25.6%after1000cycles), but PFe exhibits no capacitance nearly. In LiPF6organic electrolyte, metal salts doped polyaniline show much higher specific capacitances than PH (the specific capacitances of PLi、PZn and PMn are123F·g-1、147F·g-1and105F·g-1, but the value of PH is only47F·g-1), moreover it can greatly improve electrode cycle stability and electricity performance, but several problems such as excessive voltage drop and narrow energy storage potential range remain exist.(5) Polyaniline nanofiber materials co-doped with various metal ions and H+(PHLi、PHZn and PHMn) were prepared though in-situ doping in polymerization. Compared with that doped with H+(PH), all the co-doped polyaniline electrodes exhibit higher specific capacitance and better cycle stability (at the current density of0.1A·g-1, the specific capacitance of PHZn is419F·g-1and the degradation of capacitance is about11.8%after1000cycles).(6) HC1doping polyaniline nanofiber and activated carbon composites were prepared by in situ polymerization. When activated carbon adding quantum is30%of the mass of aniline, the composited electrode shows the lowest charge transfer resistance as well as good power capability and cycle stability in H2SO4soultion (The specific capacitance is414F·g-1at current density of0.1A·g-1and degradation of capacitance is about14.3%after1000cycles). The modified polyaniline nano fiber/carbon composites for aqueous solution (PANI/C-1) can achieve the specific capacitance of427F·g-1and the degradation of capacitance is about10%after1000cycles. Another modified polyaniline nanofiber/carbon composites for organic solution (PANI/C-2) can achieve the specific capacitance of128F·g-1in LiPF6organic electrolyte, the electrode discharge voltage drop reduced greatly and the cycle performance was also improved.