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[en] There is a need for developing new and perspective materials for oxygen reduction reaction (ORR) as one of the most essential reactions in the life processes, energy storage, and conversion, in order to exchange the most often used materials based on platinum supported/unsupported substrates, especially carbon supports. Herein, we present low-cost alternative electrode materials consisting of two silver@polyvinylpyrrolidone-polyaniline (Ag@PVP-PANI) nanocomposites that showed great potential as Pt-free ORR electrocatalysts. Simple and effective polymerization processes of aniline in the methanol, using PVP as shape-mediated stabilizator and stimulator of its oxidation by silver ions, led to the formation of nanocomposites with truncated triangular silver nanoparticles dispersed throughout granular and wrinkle-like surfaces of PANI matrix. The behavior of PVP chains in acidic conditions showed great influence on nanocomposites’ conductivities, regardless of the high silver content. Electrocatalytic survey of nanocomposites examined in alkaline media toward ORR pointed out their appreciable activities with high ORR onset potentials. Moreover, for the nanocomposite with lower silver content (18.9 wt. %), the four-electron ORR pathway was evidenced. © 2019 Elsevier B.V.
[en] Electron nuclear double resonance (ENDOR), electron nuclear nuclear (TRIPLE) resonance and electron spin echo envelope modulation (ESEEM) experiments permit a considerable enhancement in resolution relative to electron paramagnetic resonance for the determination of small hyperfine interactions. Such measurements applied to various polyacetylene samples permit determination of the wavefunction of the S = 1/2 defect (e.g., the soliton wavefunction). Experimental results are discussed in terms of various theoretical calculations. Special attention is given to discussing the limitations of both experimental and theoretical results. (Auth.)
[en] The doping of deuterated polyparaphenylene [C6D4]sub(n) with AsF5 has been investigated by real time neutron diffractometry at 100, 400 and 820 mbar AsF5 pressure. The reaction appears to be diffusion controlled. Evidence for one doped phase with partial crystalline order was obtained. Structural considerations suggest two polymer chains plus one dopant ''string'' as the repetitive unit. (Auth.)
[en] The 13C NMR spectrum analysis of electrochemically prepared poly(3-methylthienylene) films has been investigated. Both a film doped with ClO4- ions (P3MT-ClO4) and an undoped film (P3MT0) give only two distinct absorption bands through the electrochemical reduction of P3MT-ClO4. These distinct bands are definitely attributable to the methyl group (upper field) and the thiophene ring (lower field), respectively, and are characteristic of well-defined poly(3-methylthienylene). The correlation between conductivity and 13C NMR spectra is discussed. (Auth.)
[en] In spite of extensive investigation and applications, influence of oxygen (O), and humidity on polyaniline (PANI) behaviour is not well understood. For this reason we have performed semi-empirical quantum mechanics, and ab-initio calculations of the pernigraniline base (PNB) PANI oligomers, of various lengths, before and after approach of H2O, O2 , and hydroxyl (OH −) group, and attachment of OH − and O to various molecular positions. Structure, charge and electrostatic potential distribution, relevant energies and enthalpies, infrared and electronic spectra of the PNB tetramer equilibrium conformation, and their changes induced by specific OH − , and O attachments are determined. These results provide identification of the most probable positions for O2 and H2O approach to PNB_PANI, enthalpies of OH − and O attachments to them, changes of molecular properties induced by the attachments, and infrared and electronic modes that are most suitable for the attachments detection. The results are compared to the existing experimental data, and the results of similar calculations, and implications for the PNB_PANI applications are notified. © 2019 Elsevier B.V.
[en] The purpose of the present study is to examine the possibility of obtaining information on the low-frequency modes of polyacetylene by incoherent inelastic neutron scattering. Neutron energy-loss spectra were obtained using the rotating-crystal spectrometer IN4 at the Institut Laue-Langevin, Grenoble. Measurements were made at 10 K using an incident neutron energy of 85 meV. (Auth.)
[en] Using the PPP Hamiltonian model of (CH)sub(x), the authors study the effects of the Coulomb interaction on the 13C-NMR of doped (CH)sub(x) and the electronic and lattice structures of polarons. The broad asymmetric 13C-NMR signal is explained by the Coulomb-induced charge density modulation around charged solitons. Polarons accompany the Coulomb-induced charge and spin density modulations which have a dip at the centre and different spreadings, the former being wider. The lattice dimerization in polarons is not only relaxed but also reversed in a central region. A polaron accompanies four midgap levels. With a suitably screened Coulomb interaction, polaron and soliton levels can be obtained in good agreement with the data of electrochemical doping voltage spectroscopy. The positively and negatively charged solitons make a breather-like bound state, which may explain the self-pinning of photogenerated solitons. (Auth.)
[en] Recently, it has been found that the conductivity of poly(p-phenylene) (PPP) increases by more than ten orders of magnitude upon doping with certain strong electron donors or acceptors. By virtue of its sensitivity to the electronic environment of the nucleus, the solid-state NMR technique has provided important information on similar processes in the doping and conduction in polyacetylene. The authors report studies of the proton resonance in poly(p-phenylene) using multiple-pulse NMR techniques which indicate that these techniques may be useful for probing the environment of such doped conductive polyphenylenes. (Auth.)
[en] The authors have carried out a study of the frequency (23 MHz < f < 35 MHz) dependence of the proton spin lattice relaxation time, T1, of trans-(CH)sub(x) for temperatures 0.33 K < T < 4.2 K. They find that within this range T1 can be expressed as an activated quantity, T1 = A exp(-Δ/ksub(B)T), with Δ = gμsub(B)H (A and g constant). The observed effective g factor of 3.3 for the activation energy suggests that we are nearly in the low-temperature high-field limit (gμsub(B)H/ksub(B)T > 1) for one-dimensional nuclear spin diffusion to fixed electron spins. It is shown that assuming proton relaxation is due to mobile neutral solitons leads to a one-dimensional diffusion constant that increases with decreasing temperature and has an activated behaviour i.e., D = D0 exp(Δ'/ksub(B)T) with Δ' = 1.1 K. However, this latter model is in contradiction with the reported solid state effect at low temperatures. (Auth.)