New conducting salts containing unsymmetricalπ-donors

This communication describes the synthesis and the electrochemical properties of a new type of donor containing sulfur or selenium atoms: the dimethyltetramethylenetetraselenafulvalene 1 and the dimethyltetramethylenetetrathiafulvalene 2. The electrical conductivity of their charge transfer complexes and of some of their radical cation salts are reported.     

New conducting polythiophenes containing substituted polyfluorinated alkoxy chain

A series of poly(fluoroalkoxy thiophenes) have been prepared by electrochemical and chemical polymerization respectively. The substitution of thiophene by polyfluorinated alkoxy chains affords more favorable structures in electronic effect and higher stabilities of their polymers than conventional alkoxy chain substituted polymers.     

Electrical conductivity of AgI–CdI2–KI and AgI–CuI–KI ionic conducting systems

Samples of general formulae (AgI)_4?2x(CdI₂)_xKI and (AgI)_4?x(CuI)_xKI, x = 0–0.4, have been prepared and studied by conductivity measurements, powder X-ray diffraction and DSC techniques. Room temperature XRD reveals the presence of the orthorhombic K₂AgI₃ as the major component in the system. DSC traces show endothermic peaks in the temperature range of 309–330 K, depending on the sample composition. These are attributed to the solid state reaction between AgI and K₂AgI₃ to form the cubic KAg₄I₅. Impedance spectra show the prominence of electrode – electrolyte interface effect which is explained in terms of the high rate of ion migration. Ionic conductivity enhances with the increase of Cd²⁺ content, while Cu⁺ contained samples show a decrease in conductivity with increasing Cu⁺ ratio though the ionic conductivity remains higher than that of the pure one.     

Enhanced ionic conductivity in an otherwise poorly conducting Ce0.90Ca0.10O(2-δ) system

A poorly conducting ionic material Ce(0.90)Ca(0.10)O(2-δ) was converted to a highly conducting composition by a codoping strategy with Sm(3+) and Gd(3+). A 50% replacement of Ca with either Sm or Gd has increased the conductivity at 550 °C of Ce(0.90)Ca(0.10)O(2-δ) from 0.0040 to 0.0169 S/cm for the Ce(0.90)Ca(0.05)Sm(0.05)O(2-δ) composition and to 0.0184 S/cm for the Ce(0.90)Ca(0.05)Gd(0.05)O(2-δ) composition. The enhancement in the oxide ion conductivity of these codoped samples has been related to the low ionic radii mismatch and the elastic strain. The extended X-ray absorption fine structure measurements on these systems confirmed that Gd, when coupled with Ca, introduced more disorder in the system, leading to lower activation energy and higher conductivity. In addition, a reduction in the Ce-O bond distance and coordination number has also been observed with codoping.     

Highly conducting π-conjugated molecular junctions covalently bonded to gold electrodes

We measure electronic conductance through single conjugated molecules bonded to Au metal electrodes with direct Au-C covalent bonds using the scanning tunneling microscope based break-junction technique. We start with molecules terminated with trimethyltin end groups that cleave off in situ, resulting in formation of a direct covalent σ bond between the carbon backbone and the gold metal electrodes. The molecular carbon backbone used in this study consist of a conjugated π system that has one terminal methylene group on each end, which bonds to the electrodes, achieving large electronic coupling of the electrodes to the π system. The junctions formed with the prototypical example of 1,4-dimethylenebenzene show a conductance approaching one conductance quantum (G(0) = 2e(2)/h). Junctions formed with methylene-terminated oligophenyls with two to four phenyl units show a 100-fold increase in conductance compared with junctions formed with amine-linked oligophenyls. The conduction mechanism for these longer oligophenyls is tunneling, as they exhibit an exponential dependence of conductance on oligomer length. In addition, density functional theory based calculations for the Au-xylylene-Au junction show near-resonant transmission, with a crossover to tunneling for the longer oligomers.     

Proton transfer across conducting polypyrrole membrane separated by two electrolyte solutions

Electrochemical behavior of the transfer of H+ across polypyrrole membrane (PPM) was studied. The transfer process was quasi-reversible and mainly diffusion-controlled. PPM elec-tropolymerized in water solution has better reversibility than that in CH3CN solution for the transfer of H+. The transfer process of H+ across the two kinds of PPM indicated that the PPM electrochem-ically polymerized was of asymmetry.     

In-situ construction of conducting alloy interphase towards modulating Li-ion storage kinetics

Interface engineering strategy shows great promise in promoting the reaction kinetic and cycling performance in the field of electrochemical energy storage application.In this work,an in-situ interface growth strategy is proposed to introduce a robust and conducting MoGe₂ alloy interphase between the electrochemical active Ge nanoparticle and flexible MoS₂ nanosheets to modulate their Li-ion storage kinetics.The structural evolution processes of the Ge@MoGe₂@MoS₂ composite are unraveled,during which the initially-generated Ge metals serve as a crucial reduction mediator in the formation of MoGe₂ species bridging the Ge and MoS₂.The as-generated MoGe₂ interface,chemically bonding with both Ge and MoS₂,possesses multi-fold merits,including the maintaining stable framework of electrochemically inactive Mo matrix to buffer the strain-stress effect and the"welding spot"effects to facilitate the efficient Li⁺/e^-conduction.As well,the introduction of MoGe₂ interface leads to a unique sequential lithiation/de^-lithiation process,namely in the order of the electrochemically active MoS₂-MoGe₂-Ge during lithiation and vice versa,during which the electrode strain could be more effectively released.Benefited from the robust and rigid MoGe₂ interface,the delicately designed Ge@MoGe₂@MoS₂ composite exhibits an improved charge/discharge performances(866.7 mAh g^-1 at 5.0 A g^-1 and 838.5 mAh g^-1 after 400 cycles)while showing a high tap density of 1.23 g cm^-3.The as-proposed in-situ interface growth strategy paves a new avenue for designing novel high-performance electrochemical energy storage materials.     

Evaluation of kinetic stability against CO2 and conducting property of BaCe0.9−xZrxY0.1O3−δ

In order to prepare high proton conducting oxide with high chemical stability against CO₂ at 600–800 °C, preparation of BaCe_0.9?xZr_xY_0.1O_3?δ was examined. Almost single-phase could be prepared for the specimens with x = 0.0–0.2 by Pechini method. Reaction kinetics between BaCe_0.9?xZr_xY_0.1O_3?δ and CO₂ could be explained by Jander model. With increasing Zr content up to 0.2, apparent rate constant determined from Jander plot decreased by about one order, showing improvement of kinetic stability against CO₂. It was also clarified that influence of partial Zr substitution on electrical property was slight, leading to the conclusion that BaCe_0.7Zr_0.2Y_0.1O_3?δ exhibited both high kinetic stability against CO₂ and relatively high proton conduction.     

Long-term structural surface modifications of mixed conducting La2NiO4+δ at high temperatures

Abstract  

Long-term annealing of La₂NiO_4+δ single crystals at 1,273 K in air leads to the formation of nickel-rich Ruddlesden–Popper phases at the single-crystal surfaces. Both the composition and the morphology of these phases depend on the surface orientation; whereas only crystallites of La₄Ni₃O_10−δ were observed on (001) surfaces, both La₃Ni₂O_7−δ and La₄Ni₃O_10−δ were formed on (100) surfaces. The formation of the nickel-rich RP phases is believed to be due to surface segregation of nickel or evaporation of a volatile lanthanum species. The crystallographic (001) planes inside the La₃Ni₂O_7−δ and La₄Ni₃O_10−δ crystallites were found to be oriented in the direction of preferential crystallite growth, which indicates that the diffusion of lanthanum and nickel cations is faster along the crystallographic (001) planes than perpendicular to these planes.     

Electrochemically controlled transport across conducting polymer composites — Basis of smart membrane materials

Electropolymerisation procedures which allow the development of mechanically stable, conductive, pinhole-free membranes based on polypyrrole/polyvinylsulphonate or polypyrrole/Nafion have been developed.Using a new electromembrane cell design and a new electrochemical controller, the ability to electrochemically control the transport of Na⁺ or K⁺ across these membranes has been demonstrated.     

Methane oxidation in a mixed ionic–electronic conducting ceramic hollow fibre reactor module

A reactor module, consisting of six gas-tight hollow fibre membranes made of the mixed ionic–electronic conducting perovskite, , has been tested for oxygen permeation and stability during methane oxidation in the temperature range of 540 to 960°C. Rigorous leak testing was undertaken and it was demonstrated that the module could be adequately sealed. Oxygen permeation fluxes were similar to those reported by previous workers. At higher temperatures of operation, it appeared that mass transfer limited the oxygen flux, as this flux was dependent upon the flow rates on either side of the membrane. In this way, reactant flow rates could be used to manipulate the transmembrane oxygen flux. It was found that the product distribution on the methane side was dependent upon this flux, with carbon monoxide and hydrogen production being favoured at low fluxes and carbon dioxide and water production being favoured at higher fluxes. Furthermore, at low oxygen flow rates, periodic increases in the transmembrane oxygen flux were observed. The cause of this behaviour is unclear but may be as a result of phase/stoichiometric changes associated with the membrane material.     

Synthesis and characterization of electrical conducting porous carbon structures based on resorcinol–formaldehyde

Electrical conducting carbon (ECC) porous structures were explored by changing the pyrolysis temperature of organic xerogel compounds prepared by sol–gel method from resorcinol–formaldehyde (RF) mixtures in acetone using picric acid as catalyst. The effect of this preparation parameter on the structural and electrical properties of the obtained ECCs was studied. The analysis of the obtained results revealed that the polymeric insulating xerogel phase was transformed progressively with pyrolysis temperature into carbon conducting phase; this means the formation of long continuous conducting path for charge carriers to move inside the structure with thermal treatment and the samples exhibited tangible percolation behaviour where the percolation threshold can be determined by pyrolysis temperature. The temperature-dependent conductivity of the obtained ECC structures shows a semi-conducting behaviour and the I(V) characteristics present a negative differential resistance. The results obtained from STM micrographs revealed that the obtained ECC structures consist of porous electrical conducting carbon materials.     

Synthesis of conducting polyaniline—polyanion interpolymer complexes and study of their composition and properties

The polymerization of aniline in the presence of poly(4-styrenesulfonic acid) and poly(2-acryla-mido-2-methyl-1-propanesulfonic acid) results in interpolyelectrolyte complexes with a composition and a dispersion stability depending on the aniline-to-polyanion ratio in the initial reaction mixture. As opposed to polymerization mediated by poly(4-styrenesulfonic acid), the template polymerization of aniline conducted in the presence of poly(2-acrylamido-2-methyl-1-propanesulfonic acid) leads to the structural template effect that manifests itself as the formation of polyaniline containing 1,2- and 1,4-substituted benzene rings. It is found that the electron conductivity of the polyaniline-polyanion interpolyelectrolyte complexes depends not only on the content but also on the nature of the used polyacid and proves to be higher in the case of stoichiometric interpolyelectrolyte complexes formed in the presence of poly(4-styrenesulfonic acid).     

Modeling current–voltage relationships of mixed conducting cathode materials for solid oxide fuel cells

In recent decades, high-temperature oxygen reduction reaction on mixed conducting cathodes were investigated intensively by many researchers. Computational approaches as well as electrochemical and spectroscopic studies have been made to elucidate the kinetics. Contribution of oxygen vacancy to the reaction rate was suggested in multiple reports, and plausible reaction pathways were proposed based on density functional theory (DFT) calculations. The picture of oxygen reduction reaction has become clearer in these years. However, there still is a discussion about a credible formula that represents the current–voltage relationships. Discrepancies are found among the reported data on the magnitude of the rate constant and on its dependencies on partial pressure and temperature. The difference is significant between a model electrode and a practical porous electrode. Comparison of the results suggests the existence of series reaction barriers, that is, the surface reaction and subsurface transport, which should be considered for consistent representation of the total electrode process.     

Compilation of all the isothermal mass/charge transport properties of the mixed conducting La2NiO(4+δ) at elevated temperatures

It is known [H.-S. Kim and H.-I. Yoo, Phys. Chem. Chem. Phys., DOI:10.1039/c0cp00722f] that all the isothermal mass and charge transport properties of a mixed ionic electronic conductor compound can be universally represented by a 2 × 2 Onsager transport coefficient matrix. Furthermore, the three independent coefficients of the matrix can be determined from a simple relaxation experiment under the ion-blocking condition in association with the equation of state with respect to the nonstoichiometry or thermodynamic factor. By using this method, we compile the transport matrices at 800 °C, 900 °C and 1000 °C, respectively, on the system of La(2)NiO(4+δ) across its entire stability range, and calculate thereby its transport properties to compare with the literature values available. The interference effect between mobile oxygen ions and holes upon their transfer is discussed.     

Simultaneous determination of nitrophenol isomers at the single-wall carbon nanotube compound conducting polymer film modified electrode

One of the challenging areas of electrochemistry and electroanalytical chemistry is the simultaneous determination of isomers at the same electrode. Con- ventional electrode only possesses a single function of electron transfer; therefore, it is difficult…     

Polymeric proton conducting membranes for medium temperature fuel cells (110–160°C)

The availability of stable polymeric membranes with good proton conductivity at medium temperatures is very important for the development of methanol PEM fuel cells. In view of this application, a systematic investigation of the conductivity of Nafion 117 and sulfonated polyether ether ketone (S-PEEK) membranes was performed as a function of relative humidity (r.h.) in a wide range of temperature (80–160°C). The occurrence of swelling/softening phenomena at high r.h. values prevented conductivity determinations above certain temperatures. Nevertheless, when r.h. was maintained at values lower than 80%, measurements were possible up to 160°C. The results showed that Nafion is a better proton conductor than S-PEEK at low r.h. values, especially at temperatures lower than 120°C. The differences in conductivity were, however, leveled out with the increasing r.h. and temperature. While at 100°C and 35% r.h. the conductivity of S-PEEK 2.48 was about 30 times lower than the conductivity of Nafion, both membranes reached a comparable conductivity (4×10⁻² S cm⁻¹) at 160°C and 75% r.h. The effect of superacidity and crystallization of the polymers on the conductivity, as well as the possibility of using Nafion and S-PEEK membranes in medium temperature fuel cells, are discussed.     

Extraordinary high potassium ion conducting polycrystalline solids based on gadolinium oxide–potassium nitrite solid solution

A new type of potassium ion conducting polycrystalline solid electrolyte was prepared by forming the Gd₂O₃–KNO₂ solid solution. Since KNO₂ is dissolved in the Gd₂O₃ crystal lattice scale, a considerable enhancement in K⁺ ion conductivity was successfully realized. The K⁺ ion conductivity is more than three orders of magnitude higher than that of the well-known K⁺ ion conducting K₂SO₄ polycrystal solid and the value also exceeds that of K⁺–β^″-alumina single crystal, demonstrating the highest ion conductivity among the K⁺ ion conducting solid series.     

Mixed conducting polymers on ion-conducting sensor glasses – charge transfer in the system polymer/glass

Mixed ion/electron conducting polymer layers based on polypyrrole have been used as internal reference electrodes in all-solid-state pH glass electrodes. The effect of the nature and composition of the polymer used and of the deposition technique applied on the performance of the resulting sensor has been studied. For this purpose, crucial sensor properties, e.g. parameters of the calibration function, response behaviour and complex impedance, have been determined experimentally at room temperature. The results show that several properties studied remained nearly uninfluenced by changes of the polymer composition. The zero potential point of the calibration line was found to be the most sensitive parameter. Principally, almost all mixed conducting polymers used seems to result in a stable charge transfer in the system polymer/glass.     

Interfacial enzyme activation, non-lamellar phase formation and membrane fusion. Is there a conducting thread?

Previous studies from this laboratory have shown that the enzymic generation of diacylglycerol in bilayers by phospholipase C may lead to membrane fusion through the formation of transient non-lamellar lipidic intermediates. The present paper intends to explore the correlations existing among the three main processes involved, namely (a) the induction (or inhibition) of lamellar-to-non-lamellar phase transitions in lipid mixtures through the addition of small (< 5 mol%) proportions of other lipids, (b) the promotion, by the latter lipids, of fusion in otherwise stable phospholipid vesicles (large unilamellar liposomes) under conditions leading to inverted hexagonal/inverted cubic phase formation in bulk lipid systems, and (c) the modulation, by the same small proportions of lipids, of phospholipase C hydrolysis of phosphatidylcholine in liposome bilayers. It is concluded that phospholipase C may give rise to non-lamellar lipidic structures that in turn permit liposomal fusion to occur, but neither enzyme activity is directly modulated by non-lamellar phase formation, nor will whatever kind of enzyme-induced non-lamellar structure give rise to fusion. Moreover, only under certain kinetic conditions will the enzyme give rise to the organization of non-lamellar structures that are conducive to the fusion event.