Metallic nanoparticle composites oxidation reactions

The polymer resulting from oxidation of 3,5-dimethyl aniline with palladium was also studied by transmission electron microscopy (Mallick et al. 2005). As it turned out, the polymer was formed in nanofibers. During oxidative polymerization, palladium ions were reduced and formed palladium metal. The generated metal was uniformly dispersed between the polymer nanofibers as nanoparticles of 2 mm size. So, Mallick et al. (2005) achieved a polymer- metal intimate composite material. This work should be juxtaposed to an observation by Newman and Blanchard (2006) that reaction between 4-aminophenol and hydrogen tetrachloroaurate leads to polyaniline (bearing hydroxyl groups) and metallic gold as nanoparticles. Such metal nanoparticles can well be of importance in the field of sensors, catalysis, and electronics with improved performance. 

In addition to in situ reduction by the CPs, metal nanoparticles can also be synthesized on the surface of the CPs via a reduction process in the presence of other reducing agents. Yan and co-workers prepared PANI/Pt composite nanofibers by reducing a Pt salt with ethylene glycol on the surface of PANI nanofibers [78]. The diameter of PANI nanofibers was about 60 nm, and that of as-synthesized Pt nanoparticles (PtNPs) was only about 1.8 nm as calculated from X-ray diffraction (XRD) data. The small size of PtNPs on the CP matrix enhanced the electrocatalytic activity for the methanol oxidation reaction. 

After being demonstrated for the first time for transition metal oxides [POI 00], the conversion reaction (equation [1.3]) has since been expanded to a number of other elements (X = O, S, P, F, Sb...). This profound transformation of the initial material MaXb into a composite electrode made up of metallic nanoparticles and a Li X matrix enables high energy densities to be reached. Moreover, it involves redox reactions very different from those of the insertion mechanisms, which only involve the transition metal, whereas here the transition metal and post-transitional element are simultaneously reduced or oxidized. These conversion reactions thus enable more than 1 Li (le ) to be exchanged per metallic atom, and result in gravimetric and volumetric capacities that can reach 1,000 mAh/g, and 7,000 mAh/cm, respectively, which is nearly 10 times that of graphitic carbon (800 mAh/cm ). Until recently, these materials were only a laboratory curiosity since the conversion reaction, although reversible, did... 

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