Improving Electrochemical Performance Of Different Dimensional Conducting Polymer As Electrode Materials For Supercapacitors

The exhausting fossil fuel resources, escalating environmental problems and increasing energy prices highlight the urgency in developing/improving alternative clean energies and their storage technologies. Furthermore, how to use promising techniques to fabricate environmentally friendly, high-performance systems is a significant challenge in energy storage technologies in modern society. Considering these aspects, supercapacitors are considered to be one of the most promising electrochemical energy storage devices of the present century because of their high power density, faster power delivery, long cycle life compared to batteries; thus, they are potentially used in applications requiring short-term power boosts such as emergency doors,hybrid electrical vehicles and uninterrupted power sources. Electrode materials, at the heart of such an energy storage system, directly decide the capability, delivery rates and efficiency of the supercapacitor. In the past decades, conducting polymers(CPs) have been extensively tested in supercapacitors as active electrode materials. It is worth mentioning that nanostructured CPs with different dimensions have offered unique opportunities for innovative applications in supercapacitors particularly, which mainly result from their favorable characteristics at the nanoscale.Based on this case, this study introduces strategies based on design of nanostructured CPs with different dimensions aiming at improve the electrochemical performance of supercapacitors.We have accomplished the design, synthesis and performance research of the electrode materials containing: one-dimensional nanotubes, quasi-two-dimensional nanosheets and three-dimensional hierarchitectures of CPs. In addition, the morphology and microstructure of CPs-based composite were characterized by chemical and physical means, and the electrochemical properties of synthesized materials were studied as electrode materials for supercapacitors. The thesis aims at studying the structural design, growth mechanism and performance improvement of CPs-based composites with different dimensions as electrode materials, especially providing a theoreticalsupport and practical basis for the development of supercapacitor electrodes. The main conclusions are as follows:1.We report the successful synthesis of uniform PANI doped malic acid(PANI-MA)nanotubes via a facile chemical soft template method in the presence of MA serves as a dopant without any surfactant and template. We optimized the reaction conditions to obtain the perfect morphology of PANI nanotubes. In order to study the formation process of the PANI nanotubes,we monitored the morphology of the product with other organic acids, such as CA, SA, DA and SA. What’ more, hydrogen bonding plays a crucial role in the formation of the one-dimensional tubular nanostructure of PANI during the self-assembly process. The novel PANI nanotubes have been further assessed as an efficient electroactive material for supercapacitor. Electrochemical results indicated that the PANI nanotubes exhibited very high specific capacitance(658 F/g) and excellent cycling stability as electrode materials for supercapacitors. Moreover, we believe that this could be a model synthesis route for the large scale production of various CPs for supercapacitors in a very simple, low cost and environment friendly way.2.Coaxial tubular morphology based on sodium alginate-multiwalled carbon nanotubes/polyaniline(SA-MWCNTs/PANI) have been synthesized via the in situ chemical oxidative polymerization of aniline with SA-modified MWCNTs, and optimized preparation conditions were employed in order to achieve higher specific capacitance. The results show that SA-modified MWCNTs as a support material could provide more electroactive sites for nucleation of PANI as well as excellent electron diffusion path, and SA-modified MWCNTs were homogeneously coated on both surfaces with PANI nanoparticles. The effect of the MWCNTs and SA feeding ratio on the specific capacitance of the supercapacitors with the SA-MWCNTs/PANI nanocomposites as the electrode materials were investigated, and the electrical conductivity the nanocomposites were also discussed. In addition, the SA-MWCNTs/PANI nanocomposites achieved the maximum specific capacitance as high as 442 F/g at a current density of 0.5 A/g, long cycle life, and fast reflect of oxidation/reduction on high current changes, the highest value reported so far for biopolymer-doped PANI nanocomposites under the lowest doping amount of MWCNTs(0.6 wt%).3.Our aim is to utilize the well-dispersed DAS-RGO for the preparation of homogeneously dispersed DAS-RGO/PANI composite with improved electrochemical performance. The morphology and intrinsic properties of both components should be well preserved to achieve a better synergetic effect. In this work, a facile one-step in situ chemical oxidative polymerization method for the preparation of DAS-RGO/PANI composite is first time reported, which exhibitedvery good performance as supercapacitor electrode. Due to the good dispersibility of DAS-RGO and the mild reaction condition, a homogeneous dispersion of individual graphene sheets within PANI was achieved and the morphology as well as intrinsic properties of both components was well preserved, which has a vital impact on the improvement of the specific capacitances of the DAS-RGO/PANI composite. The resulting composite achieved the maximum specific capacitance as high as 499 F/g at a current density of 0.5 A/g, the highest value reported so far for graphene-doped PANI composite via a green and facile approach of reduced graphene oxide. In addition, the DAS-RGO/PANI composite acquired the outstanding conductivity of 832.1 S/m, low resistance, long cycle life, and fast reflect of oxidation/reduction on high current changes.4.We report the one-step synthesis of PEG-CHO modified graphene oxide/ conducting polymers(APGO/CPs) quasi-two-dimensional materials by in situ oxidation polymerization of conducting polymer monomers to form well-defined flake-like CPs nanosheet arrays on the APGO sheets. Experiment results showed that PEG-CHO can not only act as anchor sites to combine with the amine nitrogens of the PANI or PPy chains, but also facilitate the diffusion and growth of polymer monomers on the surface of GO sheets. Moreover, APGO as conducting networks can provide large surface and more electronic transport paths for conductive networks inside the bulk electrode matrix, which effectively improve the capacitive capability and cycling stability of APGO/CPs material. As a result, APGO/CPs composites exhibit excellent electrochemical performance as a supercapacitor electrode material thanks to its high-efficiency charge-transfer tissue architecture. The composites of APGO/PANI and APGO/PPy display specific capacitances of 522 and 404 F/g at 0.5 A/g, respectively, as well as improve rate performance and excellent cycle ability. Furthermore, high conductivity values and low internal resistance are obtained, and the effect of microstructure on the electrochemical performance of the composites was also investigated.5.The novel polypyrrole/graphene oxide(PPy-GO) hierarchitectures of uniform PPy nanospheres and GO have been synthesized by in situ polymerization method. The morphology and structure of the PPy-GO composites were studied by means of techniques. Experimental results showed that PPy nanospheres with small nanospheres of only ~70 nm were uniformly grown on the GO sheets to form continuous 3D PPy-GO hierarchitectures. The smaller size of PPy can not only be more beneficial to increasing the electrochemical performance, but can also reduce ion diffusion path and make higher material utilization. Moreover, the well-designed 3D hierarchitectures and synergistic effects of PPy-GO composites can clearly lead to high rates of electrode reaction and good electrode/electrolyte contact areas. The specific capacitance ofPPy-GO nanocomposite can reach up to 370 F/g at a current density of 0.5 A/g with a large mass loading of 8.0 mg/cm2. It is noteworthy that the cycling stability of PPy-GO electrode was improved significantly by the 3D hierarchitectures, and showed excellent capacitance retention(91.2%) even after 4000 cycles, suggesting its attractive application in supercapacitors with improved performance.