Preparation And Applications Of Graphene/Polyaniline, Polypyrrole And Its Copolimer Nanocomposites Materials

Polyaniline and polypyrrole are well known to possess many advantages such as unique electrochemical activity, strong chemical stability, cheap and easy preparation and so on. Copolymers of aniline and pyrrole have been synthesized in order to obtain great improvements on the conductivity, specific capacitance and thermal stability. However the application range of conducting polymer is limited due to their worse mechanical properties and electrochemical cycle stabilities, which can be solved by combining conducting polymer with graphene sheets which have high surface area and high conductivity.To obtain high-performance nanocomposites as supercapactive electrode materials and gas sensing materials, three nanocomposites were prepared by covering graphene sheet with polyaniline, polypyrrole and their copolymer thin layers through in situ chemical oxidative polymerization, respectively, in which graphene sheets were used as the conductive substracts for aniline and pyrrole, and their structures and properties were discussed. Main results and conclusion are listed as follows:1. Influence of graphene sheet on the conformation of conducting polymersThe as-prepared nanocomposites were characterized by FE-SEM, SPM, Raman, FT-IR and electrochemical measurements in different electrolytes, and the influences of graphene sheets on the (?) growth of conducting polymer chains were discussied. The uniform nanocoating of the conducting polymer film on the surface of graphene sheets was sucessively achieved, and the improvement on the conjugate degree of polymeric chains. For the copolymer, the polyaniline layers formed close to the surface of graphene sheets, and the nanocomposite exhibited a sandwich-like structure, in which a thin layer of polyaniline was inserted between graphene sheet and polypyrrole thin layer. This can be further demonstrated from the results about electrochemical behaviors in different electrolytes. The formation of such sandwich-like structure benifited from strong interaction between the graphene hexatomic ring structure and polyaniline chain, and the difference in the polymerization mechanism between aniline and pyrrole monomers.2. Graphene/conducting polymer nanocomposites as supercapacitor electrode materialsThree kinds of supercapacitor electrodes were fabricated by using above-mentioned nanocomposites, and their electrochemical performances were evaluated and the differences were compared. It is found that all the nanocomposites have wider electrochemical window (2 V) than that of those previously reported. It is further found that the best capacitive properties can be obtained for the nanocomposite with the mass ratio of graphene sheet to conducting polymer of 3:2. For each nanocomposites with different polymeric fraction, the maximum specific capacitance values for graphene/polyaniline, graphene/polypyrrole and graphene/poly(aniline-co-pyrrole) are 496,504, and 541 F/g, respectively. By integrating outstanding advantages of polyaniline and polypyrrole, graphene/poly(aniline-co-pyrrole) nanocomposites exhibited excellent energy storage properties, such as large inner surface region available for the charge storage of 37.59%, high charging-discharging efficiency of 97.7%, high energy density of 94.1 Wh/kg and large power density of 12.7 kW/kg. In addition, low charge transfer resistance and high cycle-life stability with 86% specific capacitance retained after 500 cycles can be also achieved.3. Graphene/conducting polymer nanocomposites as gas sensing materialsThree kinds of chemoresistive gas sensors were fabricated, and the sensing behaviours of graphene/conducting polymer nanocomposite for detecting volatile organic compounds were studied. It is found that only graphene/polyaniline can display good response and high repeatability to organic vapors, especially for ammonia gas and formaldehyde gas. It is found that the nanocomposite with the layer thickness of 3.1 mm exhibited the best sensing performance. For ammonia gas detection, a wide linear response range from 50～10000 ppm,100 s response time, 1.0×10-3/ppm sensitivity and 10 ppm detection limit cab be achieved. For formaldehyde gas, a linear response range from 20-250 ppm,101 s response time, 1.1×10-3/ppm sensitivity and 4 ppm detection limit cab be achieved. The remarkable properties benefited from the absorption of organic vapors on the surface of graphene sheets, and strong interaction or even revisable reaction between polyaniline and organic vapor molecules.