Metallic poly aniline

The passivation of conventional metals by the new organic metal Poly aniline consists of two contributions ... 

S. Kuroki, Y. Hosaka, C. Yamauchi, S. Nagata, M. Sonoda, N solid-state nuclear magnetic resonance study ofpyrolyzed metal-poly aniline cathode catalysts for oxygen reduction in fuel cells, J. Power Sources 290 (2015) 8—13. 

Tetra(o-aminophenyl)porphyrin, H-Co-Nl TPP, can for the purpose of electrochemical polymerization be simplistically viewed as four aniline molecules with a common porphyrin substituent, and one expects that their oxidation should form a "poly(aniline)" matrix with embedded porphyrin sites. The pattern of cyclic voltammetric oxidative ECP (1) of this functionalized metal complex is shown in Fig. 2A. The growing current-potential envelope represents accumulation of a polymer film that is electroactive and conducts electrons at the potentials needed to continuously oxidize fresh monomer that diffuses in from the bulk solution. If the film were not fully electroactive at this potential, since the film is a dense membrane barrier that prevents monomer from reaching the electrode, film growth would soon cease and the electrode would become passified. This was the case for the phenolically substituted porphyrin in Fig. 1. 

Polymers consisting of but not limited to poly thiophene, polypyrrole and poly aniline have been extensively used to make polymer nanofibers. In general, any metal that can be electroplated has most likely appeared in a nanowire. Semiconductors, polymers, and insulators have also been used in the design of nanowires.Furthermore, different metals can be plated in succession to give striped nanowires. 

After Little s proposal, many researchers have pursued such an exciting system in vain. Even metallic behavior was rarely seen in doped organic polymers, gels, and actuators. As mentioned in Sect. 3.4.4, MCso with linearly polymerized Ceo" exhibited one-dimensional (M = Rb, Cs) or three-dimensional (M = K) metallic behavior [144]. Recently a doped poly aniline was reported to exhibit a metallic temperature dependence for a crystalline polymer chemical oxidation of monomers grew crystallite polyaniline [329] early doping studies on polypyrrole (PFg) and poly(3,4-ethylene-dioxythiophene)X (X = PFg, BF4, and CF3SO3) prepared by electrooxidation at low temperatures also showed a metallic temperature dependence below 10-20 K (Scheme 16) [330, 331]. 

Returning to Fig. 2.19(A), we can compare the observed potential dependence for the oxidation of NADH with the electrochemistry and changes in conductivity of the poly(aniline) film over the same potential range plotted in Fig. 2.19(B). Comparing Figs. 2.19(A) and (B), it is clear that there is no response to NADH when the film is at its maximum conductivity—between -0.075 and -0.05 V vs. SCE. This supports the idea that the oxidation of NADH is a chemical reaction mediated by particular structural units within the poly(aniline) film, rather than the film acting as a metallic electrode. In the discussion below, we will return to the potential dependence once the mechanism has been established. 

In addition to creating semiconductor or metal replicas of the channels of mesoporous materials, which are expected to display electron and hole quantum confinement effects, forming fibers of polymers could lead to materials with novel electrical, magnetic, optical or mechanical properties. To this end, oxidative polymerization of aniline within the channels of mesoporous silica has been reported [91]. Convincing spectroscopic evidence for intrachannel polymerization of aniline to poly(aniline) was provided. Extracted polymer had a molecular weight considerably smaller than that of the bulk material under similar conditions indicative of a diffusion constraint imposed upon the polymerization and growth of monomer inside the channel space of mesoporous silica. 

Nickel-cadmium cell Ni-Cd cell Nickel-iron rechargeable cell -> Edison cell Nickel-metal hydride cell - Ni-MFlcell Nicotinamide adenine dinucleotide - NADH Nigraniline - poly aniline... 

In electrochemical polymerization a solution of monomer is oxidized or reduced at the electrode surface to generate reactive radical species which couple together and produce an adherent polymer film at the electrode. The films can be electronically conducting, as in the case of pyrroles, anilines, thiophenes, etc redox conductors in which conduction occurs by self-exchange between discrete redox sites attached to the polymer, as in metal poly(pyridine) complexes or insulating, as in the case of phenols, 1, 2-diaminobenzene, etc. 

Fig. 5.57. Schematic design of an ATR element coated with a metal grid as conducting support for a poly aniline layer top) three-electrode cell arrangement for FTIR-ATR spectro-electrochemistry [268] (bottom)...

Information concerning the polymerization conversions of metallochelate monomers has appeared in the last few years. Radical polymerization has been applied to the production of metal poly(/ -acryloxyphenyltriphenylporphyrinates [4 and references therein]. Also, Cu(II), Ni(Il), Cd (II) and U02(II) have been polymerized with 5-vinylsalicylidene aniline by boiling in dimethylolpropionic acid in the presence of AIBN [88], In the case of the nitrate or acetate of U02 ... 

E. Mena-Osteritz, Superstructures of self-organizing thiophenes. Adv. Mater., 14, 609 (2002). S. T. Yau, J.N. Barisci, and G.M. Spinks, Tunneling spectroscopy and spectroscopic imaging of granular metallicity of poly aniline. Appl. Phys. Lett., 74, 667 (1999). 

Another way of introducing pre-synthesized metal NPs into nanocomposite materials is mixing with pre-synthesized CPs. It has been shown that simple mixing of PANI with a Pd suspension [73,74] and PEDOT-PSS with Au and Ag dispersions [75] results in the formation of the corresponding metal particle-CP nanocomposites in solution. The encapsulation of pre-synthesized Au NPs in pre-prepared water-soluble poly(aniline-2-carboxylic acid) was found to result in the formation of a composite nanocolloid that remains stable in aqueous solution [76]. 

The analysis given in the previous sections assumes that at heavy doping concentrations, polyacetylene (and other conducting polymers) have the electronic structure of metals. Only in a few cases has this been checked in detail. For example, the existence of a temperature independent Pauli susceptibility has been established for polyacetylene and poly thiophene, indicative of a metallic system with a finite density of states at the Fermi surface. For poly aniline, a Pauli contribution to the susceptibility has been inferred, only dominates in the most ciystaUine material. 

The discovery 5 th when in solution in concentrated sulfuric acid, poly aniline is in the protonated form, [B-NH-B-NH-]+ n, and that it is recovered as the partially crystalline salt, [B-NH-B-NH-]+ n(HS04 )n, from solutions in sulfuric acid O y precipitation in water or methanol) has opened the way to a more complete characterization of the polymer, and to studies directed toward the determination of the intrinsic properties of the ordered material. For example, the temperature independence of the spin susceptibility of the more highly ordered crystalline material above 125K is consistent with the Pauli spin susceptibility expected for a metal,with a density of states at the Fermi level estimated as 1 state per eV per formula unit (two rings). 

A. Kitani, K. Satoguchi, K. Iwai, S. Ito, Electrochemical behaviors of poly-aniline/polyaniline-sulfonic acid composites, Synthetic Metals 1999, 102, 1171. 

In the case of polythiophene doped with PF, the experimental results indicate that while at ordinary temperatures the conductivity is activated, at lower temperatures from 35 to 80 K the polymer exhibits metallic behavior [56] similar to that of poly aniline. A dependence has been found for the resistance of PT, and a resistance linear in Thas been found for P3MeT doped with CIO4", At even lower temperatures, there is a metal-to-insular transition. 

Fig. 8. First discharge curves of (a) V2O5 xerogel dried at 100°C, (b) poly(aniline)—V2O5 nanocomposite as prepared, without treatment, (c) V2O5 xerogel dried at 250°C, and (d) poly(aniline)-V20s nanocomposite treated at 80°C for 5 h, as a cathode material by coupling with a lithium metal anode using 1 M LiC104 in a 1 1 mixture of ethylene carbon-ate/dimethoxyethane as electroljde (note x is the ratio intercalated Li /V205). From Ref. 51, with permission.

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