Preparation Of Nanocomposites Based On Polvaniline And Their Application As Supercapacitor Electrodes

Supercapacitors, also called ultracapacitors, are promising energy storage devices which bridge the gap between batteries and conventional capacitors. They can provide higher energy density than conventional capacitors and much higher power density than batteries. Supercapacitors exhibit a promising set of features such as high power density, fast charge/discharge rate, sustainable cycling life, and safe operation. Based on the charge storage mechanism, supercapacitors can be divided into two categories. One is electrochemical double layer capacitor (EDLC), which stores charges electrostatically via reversible ion absorption at the electrode/electrolyte interface. EDLCs can provide ultrahigh power and excellent cycle life due to fast and nondegradation process between electrode active materials and electrolyte. However, the energy density of EDLC is limited by the finite electrical charge separation at the interface of electrode materials and electrolyte, and the availability of surface area. The other is the pseudocapacitor or redox supercapacitor, which stores energy by fast and reversible redox reactions. Because of the Faradaic process underpinning the energy stored in a pseudocapacitor, the pseudocapacitor often suffers from lack of stability during cycling. In this work, we want to fabricate electrode materials to combine these two charge storage mechanisms (Faradaic and non Faradaic), their synergic effects to improve device characteristics.Polyaniline (PANI), as a kind of widely studied electronically conducting polymers, is a promising candidate for electrode materials due to excellent capacities for energy storage, easy synthesis, non-toxic and low cost. Compared with metallic oxide, PANI possesses better conductivity. Its electrical properties can be modified by the oxidation state of the main chain and degree of protonation. And most importantly, the structures of PANI can be controlled by template-induced or self-assembly in different experimental conditions. Therefore, we want to design various structures of PANI composites, characterize their electrochemical properties, and reveal the relationship among composition, structure and performances.Sodium Alginate (SA) consists of a linear block co-polymer of1,4-linked (3-D-mannuronic (M) and R-L-guluronic acid (G), bearing abundant carboxyl and hydroxyl groups. We synthesized various templates of SA by controlling pH values of aqueous solution, and then fabricated the PANI/SA composites by in situ polymerization. The electrochemical characterization reveals that the electrode (PANI/SA) with large scale net-work structure exhibits a high electrochemical performance. PANI/SA nanofibers possess thin diameters (50-100nm), large specific surface area (65.5m2g-1) and an appropriate pore size distribution. The nanostructure of electrode materials generates high electrode/electrolyte contact area and short path lengths for electronic transport and electrolyte ion. The specific capacitance of an optimum electrode is up to1612F g-1and it maintains74%after1000cycles. The approach is simple and can be easily extended to fabricate nanostructural composites for supercapacitor electrode materials.Polyhedral oligomeric silsesquioxane (POSS),(RSiO1.5)n, has a cubic silica core with a diameter of0.53nm and a spherical radius of1-3nm including the functionalized organic arms. POSS is often used as an additive in nanoreinforced organic-inorganic hybrid materials. In this work, POSS was functionalized by direct sulfonation, and the porous and ordered hierarchical nanostructure of polyaniline/sulfonated polyhedral oligosilsesquioxane (PANI/SOPS) was subsequently fabricated by in situ polymerization. The morphologies of the PANI/SOPS nanocomposites can be controlled by adjusting the concentration of SOPS. Comparing with the pure PANI, the PANI/SOPS electrode exhibits a higher specific capacitance of1810F g-1, faster reflect of oxidation/reduction on high current changes and better cyclic stability. The specific capacitance maintains82%after3000cycles. The excellent performance may be attributed to the nano-architecture of electrode materials and the support of the SOPS nanoparticles.Synergetic interaction between PANI and SOPS significantly improves the porosity and the stability of electrode, yielding excellent electrochemical property. This result suggests that the construction of porous and ordered hierarchical nanostructure is a novel and effective way for improving the electrochemical properties of conducting polymersGraphene has attracted much research attention due to its two-dimensional and unique physical properties, such as high electronic transport properties, excellent mechanical strength, and elasticity and superior thermal conductivity. We designed and prepared a series of polyaniline/graphene (PANI/G) composites. A modified chemical exfoliation method was used to produce graphene. In chemical reduction stage, the DMF/H2O (9:1) mixed solution was used as reaction solution instead of conventional aqueous solution. We obtained individual disperse graphene, subsequently fabricated PANI/G composites via in situ polymerization. The electrochemical characterization demonstrated that the PANI/G electrode with6%graphene content exhibits relatively high specific capacitance (846F g-1) and good long-term cycling stability. After1000cycles, the discharge capacitance retention of the PANI/G electrode is74%while that of the pure PANI is only43%. Graphene improves the stability and conductivity of electrode materials structures, so the PANI was effectively utilized.The high quality and large-area graphene were obtained by the electrochemical exfoliation of graphite in Na2SO4electrolyte. Aniline monomer was adsorbed on the nanosheets to prepare PANI/G composites via in situ polymerization. The electrochemical characterization demonstrated that PANI is effectively utilized with the assistance of graphene conductive skeletons in the electrode. The composites electrodes achieve a good specific capacitance of895F g-1at1A g-1and long-term life. It may be due to the net-work of graphene in composites, which not only support a skeleton for PANI matrix but also supply paths for electronic transport.Expanded graphite (EG) is a kind of modified graphite with a hierarchical porous nature and good conductivity. In this work, EG was exfoliated by sonication with a cylindrical tip. The exfoliation degree of EG can be controlled by ultrasonic time. The EG flakes were coated by PANI using in-situ polymerization. The electrochemical characterization illustrated that the long ultrasonic time of EG flakes had a negative effect on the electrochemical properties of PANI/EG electrodes. SEM images revealed that the EG three-dimensional (3D) structure aggravated under long time sonication, and graphene sheets intercalated into random PANI nanorods. While the ordered PANI nanorods grew onto EG flakes with no or short time sonication. The EG supplied more effectively mechanical skeleton for PANI and transport paths for ions and electron than graphene, therefore the carbon supports of EG for PANI composite electrodes is more effective.The above experiment results are very interesting, arising our future attention. An oriented array of polyaniline (PANI) nanorods grown on expanded graphite (EG) nanosheets were fabricated by in situ polymerization. The morphologies of PANI/EG nanocomposites can be controlled by changing the ratio of EG to aniline monomer. The PANI/EG nanocomposites exhibited high specific capacitance, high rate capability and significant cyclic stability. An excellent specific capacitance as high as1665F g-1was observed in the PANI/EG electrode with10%EG content. The composite electrode material also exhibited significant rate capability with specific energy of113.8Wh kg-1and specific power of560kW kg-1at the current density of8A g-1, respectively, and good long-term cycling stability. In composites, EG serves as excellently3D conductive skeletons to support a highly electrolytic accessible surface area of redox active PANI and supply a direct path for electrons. Such3D nanoarchitecture composite is very promising for the next generation of high performance electrochemical supercapacitors.