Sol-Gel Synthesis And Characterization Of Molybdenum Oxide/Polypyrrole Hybrids
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nanocomposites with MoO3 and various conducting polymers (such as poly(aniline), polypyrrole, and poly(para-phenylene)) has been reported by Nazar et al through an ion exchange method where the monomer is inserted between the MoO3 layers and oxidatively polymerized [8,9]. This paper presents novel synthesis techniques through which MoOa/PPy hybrid aerogels and xerogels have been synthesized successfully. The sol-gel technique provides a method where molecular mixing of the different components can occur while yielding a high surface area endproduct. Through this technique, it is anticipated that the molecular level mixing can better maximize the advantages of both compounds while enhancing intercalation reactions through the high surface area materials. Preliminary data show that the hybrid does indeed have higher electrical conductivity and higher initial lithium capacity as compared to that of MoO 3 gels. Physical, electrical, and electrochemical properties of the MoO 3/PPy hybrids are reported. EXPERIMENTAL METHODS There were two general routes taken to synthesize the MoO 3 /PPy hybrid. Both involve first forming a molybdenum oxide sol, details of which were reported previously [10]. In the first route (samples A), the pyrrole monomer (Aldrich) was added immediately upon formation of the sol and then allowed to age in closed containers. Gelation occurred in approximately I week. In the second route (samples B), the sol was allowed to age in closed containers first, then shortly before gelation the pyrrole monomer was added. Gelation occurred within 1-3 days after the addition of the monomer. Concentration of the monomer ranged from 0.3 to 0.6 moles of Py/Mo for both types of samples. 269 Mat. Res. Soc. Symp. Proc. Vol. 576 © 1999 Materials Research Society
After gelation, the samples were aged in closed containers for 1-2 weeks. Aerogels were formed by supercritically drying as described by Chaput et al. [11]. Xerogels were formed by opening the containers to air for 2-3 days then heat treating at 100°C for 2-3 hours. Chemical analysis was performed by Galbraith Laboratories, Inc. Nitrogen gas adsorption analysis (Micromeritics, ASAP 2010) was used to determine the surface area of the aerogels and xerogels by the BET method. The BJH method was used in determining the average pore diameter. The bulk densities of the gels were determined with a Hg pycnometer while the skeletal densities were measured with a gas pycnometer (Micromeritics, AccuPyc 1330). Transmission electron microscopy (JEOL, IOOCX) was used to help determine the structure and morphology of the gels. FTIR measurements (Nicolet, 510P) were used to establish bond formation of the hybrid. The electrical conductivity of the MoO 3/PPy hybrid gels was measured from 150'C to 30'C by the complex impedance method (Hewlett Packard 4284A LCR meter). For these measurements, powders of the hybrids were pressed into pellets and gold electrodes sputtered on opposite sides.
The electrochemical behavior was determined for a crushed gel mixed with conductive carbon
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