Transformation of proton-conducting Perovskite-type into fluorite-type fast oxide ion electrolytes using a CO2 capture technique and their electrical properties

Fast oxide ion conducting Ce 1- x M x O 2-delta (M = In, Sm; x = 0.1, 0.2) and Ce 0.8Sm 0.05Ca 0.15O 1.825 were prepared from the corresponding perovskite-like structured materials with nominal chemical composition of BaCe 1- x M x O 3-delta and BaCe 0.8Sm 0.05Ca 0.15O 2.825, respectively, by reacting with CO 2 at 800 degrees C for 12 h. Powder X-ray diffraction (PXRD) analysis showed the formation of fluorite-type CeO 2 and BaCO 3 just after reaction with CO 2. The amount of CO 2 gained per ceramic gram was found to be consistent with the Ba content. The CO 2 reacted samples were washed with dilute HCl and water, and the resultant solid product was characterized structurally and electrically employing various solid-state characterization methods, including PXRD, and alternating current (ac) impedance spectroscopy. The lattice constant of presently prepared Ce 1- x M x O 2-delta and Ce 0.8Sm 0.05Ca 0. 15O 1.825 by a CO 2 capture technique follows the expected ionic radii trend. For example, In-doped Ce 0.9In 0.1O 1.95 (In (3+) (VIII) = 0.92 A) sample showed a fluorite-type cell constant of 5.398(1) A, which is lower than the parent CeO 2 (5.411 A, Ce (4+) (VIII) = 0.97 A). Our attempt to prepare single-phase In-doped CeO 2 samples at 800, 1000, and 1500 degrees C using the ceramic method was unsuccessful. However, we were able to prepare single-phase Ce 0.9In 0.1O 1.95 and Ce 0.8In 0.2O 1.9 by the CO 2 capture method from the corresponding barium perovskites. The PXRD studies showed that the In-doped samples are thermodynamically unstable above 800 degrees C. The ac electrical conductivity studies using Pt electrodes showed the presence of bulk, grain-boundary, and electrode contributions over the investigated temperature range in the frequency range of 10 (-2)-10 (7) Hz. The bulk ionic conductivity and activation energy for the electrical conductivity of presently prepared Sm- and (Sm + Ca)-doped CeO 2 samples shows conductivities similar to those of materials prepared by the ceramic method reported in the literature. For instance, the conductivity of Ce 0.8Sm 0.2O 1.9 using the CO 2 capture technique was determined to be 4.1 x 10 (-3) S/cm, and the conductivity of the same sample prepared using the ceramic method was 3.9 x 10 (-3) S/cm at 500 degrees C. The apparent activation energy of the area-specific polarization resistance for the symmetric cell (Sm,Sr)CoO 3- x |Ce 0.8Sm 0.2O 1.9|(Sm,Sr)CoO 3- x was determined to be 1 eV in air.     

Double NASICON-type cell: ordered Nd3+ distribution in Li0.2Nd0.8/3Zr2(PO4)3

The NASICON compound Li(0.2)Nd(0.8/3)Zr(2)(PO(4))(3), synthesized by a sol-gel process, has been structurally characterized by TEM and powder diffraction (neutron and X-ray). It crystallizes in the space group R3[combining macron] (No. 148): at room temperature, the Nd(3+) ions present an ordered distribution in the [Zr(2)(PO(4))(3)](-) network which leads to a doubling of the classical c parameter (a = 8.7160(3) A, c = 46.105(1) A). Above 600 degrees C, Nd(3+) diffusion occurs leading at 1000 degrees C to the loss of the supercell. This reversible cationic diffusion in a preserved 3D [Zr(2)(PO(4))(3)](-) network is followed through thermal X-ray diffraction. Ionic conductivity measurements have been undertaken by impedance spectroscopy, while some results concerning the sintering of the NASICON compound are given.     

The effective charge number and diffusion coefficient of cationic cytochrome c in aqueous solution.

The diffusion coefficient and the effective charge number of cytochrome c as a function of ionic strength, temperature and pH have been measured. The measurements were carried out using a method based on a convective diffusion process across a porous membrane. The effect of ionic strength was studied in an NaCl solution the concentration of which varied from 0.001 to 1.0 M. The temperature range studied was 10-50 degrees C, and the pH values studied were 4.0, 6.5 and 8.25. The diffusion coefficient is fairly constant as a function of ionic strength and pH, and Walden's rule is valid in the temperature range studied. The effective charge number is practically constant (ca. 2) in the concentration range studied, except in 0.001 M solution, where it is the same as the titrated value. The charge number decreases slightly in the temperature range 10-30 degrees C, but seems to drop suddenly to zero at ca. 40 degrees C. Measurements using heavy water (D2O) as a solvent instead of water did not give zero charge at 40 degrees C for cytochrome c.     

Kinetics of oxygen exchange over CeO2-ZrO2 fluorite-based catalysts

The kinetics of 18O/16O isotopic exchange over CeO2-ZrO2-La2O3 and Pt/CeO2-ZrO2 catalysts have been investigated under the conditions of dynamic adsorption-desorption equilibrium at atmospheric pressure and a temperature range of 650-850 degrees C. The rates of oxygen adsorption-desorption on Pt sites, support surface, oxygen transfer (spillover) from Pt to the support as well as the amount of oxygen accumulated in the oxide bulk, and oxygen diffusion coefficient were estimated. The nanocrystalline structure of lanthana-doped ceria-zirconia prepared via the Pechini route with a developed network of domain boundaries and specific defects guarantees a high oxygen mobility in the oxide bulk (D = (1.5 / 2.0).10-18 m2 s-1 at 650 degrees C) and allows accumulation of over-stoichiometric/excess oxygen. For Pt/CeO2-ZrO2, oxygen transfer from Pt to support (characteristic time < 10-2 s) was shown to be responsible for the fast exchange between the gas-phase oxygen and oxygen adsorbed on the mixed oxide surface. The rate of direct exchange between the gas phase and surface oxygen is increased as well due to the increased concentration (up to 2 monolayers) of surface/near subsurface oxygen species accumulated on the oxygen vacancies (originated from the incorporation of highly dispersed Pt atoms). The characteristic time of diffusion of the oxygen localized in the subsurface layers is about 1 s. The overall quantity of over-stoichiometric oxygen and/or hydroxyl groups accumulated in the bulk can reach the equivalent of 10 monolayers, and characteristic time of oxygen diffusion within the bulk is about 20 s. All these kinetic data are required for the further step of modeling partial oxidation of hydrocarbons under steady- and unsteady-state conditions.     

Distinct difference in ionic transport behavior in polymer electrolytes depending on the matrix polymers and incorporated salts

Two different electrolyte salts, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and a room temperature ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMITFSI), were incorporated into network polymers to obtain ion-conductive polymer electrolytes. Network polymers of poly(ethylene oxide-co-propylene oxide) (P(EO/PO)) and poly(methyl methacrylate) (PMMA) were chosen as matrixes for LiTFSI and EMITFSI, respectively. Both of the polymer electrolytes were single-phase materials and were completely amorphous. Ionic conductivity of the polymer electrolytes was measured over a wide temperature range, with the lowest temperatures close to or below the glass transition temperatures (Tg). The Arrhenius plots of the conductivity for both of the systems exhibited positively curved profiles and could be well fit to the Vogel-Tamman-Fulcher (VTF) equation. The conductivity of the PMMA/EMITFSI electrolytes was higher at most by 3 orders of magnitude than that of the LiTFSI/P(EO/ PO) electrolytes at ambient temperature. When the ideal glass transition temperature, T0 (one of the VTF fitting parameters), was compared with the Tg, a difference in the ionic conduction was apparent in these systems. In the P(EO/PO)/LiTFSI electrolytes, the T0 and Tg increased in parallel with salt concentration and the T0 was lower than the Tg by ca. 50 degrees C. On the contrary, the difference between the T0 and the Tg increased with increasing content of PMMA in the PMMA/EMITFSI electrolytes, with the observed difference in the concentration range studied reaching up to ca. 100 degrees C. The conductivity at the Tg, sigma(Tg), for the LiTFSI/P(EO/PO) electrolytes was on the order of 10(-14-)10(-13) S cm(-1) and increased with increasing salt concentration, whereas that for the PMMA/EMITFSI polymer electrolytes reached 10(-7) S cm(-1) when the concentration of PMMA was high. The ion transport mechanism was discussed in terms of the concepts of coupling/decoupling and strong/fragile for the two different polymer electrolytes.     

Electrochemical impedance spectroscopy of mixed conductors under a chemical potential gradient: a case study of Pt|SDC|BSCF

The AC impedance response of mixed ionic and electronic conductors (MIECs) exposed to a chemical potential gradient is derived from first principles. In such a system, the chemical potential gradient induces a gradient in the carrier concentration. For the particular system considered, 15% samarium doped ceria (SDC15) with Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-delta) (BSCF) and Pt electrodes, the oxygen vacancy concentration is a constant under the experimental conditions and it is the electron concentration that varies. The resulting equations are mapped to an equivalent circuit that bears some resemblance to recently discussed equivalent circuit models for MIECs under uniform chemical potential conditions, but differs in that active elements, specifically, voltage-controlled current sources, occur. It is shown that from a combination of open circuit voltage measurements and AC impedance spectroscopy, it is possible to use this model to determine the oxygen partial pressure drop that occurs between the gas phase in the electrode chambers and the electrode|electrolyte interface, as well as the interfacial polarization resistance. As discussed in detail, this resistance corresponds to the slope of the interfacial polarization curve. Measurements were carried out at temperatures between 550 and 650 degrees C and oxygen partial pressure at the Pt anode ranging from 10(-29) to 10(-24) atm (attained using H(2)/H(2)O/Ar mixtures), while the cathode was exposed to either synthetic air or neat oxygen. The oxygen partial pressure drop at the anode was typically about five orders of magnitude, whereas that at the cathode was about 0.1 atm for measurements using air. Accordingly, the poor activity of the anode is responsible for a loss in open circuit voltage of about 0.22 V, whereas the cathode is responsible for only about 0.01 V, reflecting the high activity of BSCF for oxygen electro-reduction. The interfacial polarization resistance at the anode displayed dependences on oxygen partial pressure and on temperature that mimic those of the electronic resistivity of SDC15. This behavior is consistent with hydrogen electro-oxidation occurring directly on the ceria surface and electron migration being the rate-limiting step. However, the equivalent resistance implied by the oxygen partial pressure drop across the anode displayed slightly different behavior, possibly indicative of a more complex reaction pathway.     

Electrical properties and defect chemistry of TiO2 single crystal. I. Electrical conductivity

The present work reports the electrical properties of high-purity single-crystal TiO(2) from measurements of the electrical conductivity in the temperature range 1073-1323 K and in gas phases of controlled oxygen activities in the range 10(-13) to 10(5) Pa. The effect of the oxygen activity on the electrical conductivity indicates that oxygen vacancies are the predominant defects in the studied ranges of temperature and oxygen activities. The electronic and ionic lattice charge compensations were revealed at low and high oxygen activities, respectively. The determined semiconducting quantities include: the activation energy of the electrical conductivity (E(sigma) = 125-205 kJ.mol(-1)), the activation energies of the electrical conductivity components associated with electrons (E(n) = 218 kJ.mol(-1)), electron holes (E(p) = 34 kJ.mol(-1)), and ions (E(i) = 227 kJ.mol(-1)), and the enthalpy of motion for electronic defects (DeltaH(m) = 4 kJ/mol). The electrical conductivity data are considered in terms of the components related to electrons, holes, and ions. The obtained data allow the determination of the n-p demarcation line in terms of temperature and oxygen activities. The band gap determined from the electronic component of the electrical conductivity is 3.1 eV.     

A new high-temperature multinuclear-magnetic-resonance probe and the self-diffusion of light and heavy water in sub- and supercritical conditions

A high-resolution nuclear-magnetic-resonance probe (500 MHz for 1H) has been developed for multinuclear pulsed-field-gradient spin-echo diffusion measurements at high temperatures up to 400 degrees C. The convection effect on the self-diffusion measurement is minimized by achieving the homogeneous temperature distributions of +/-1 and +/-2 degrees C, respectively, at 250 and 400 degrees C. The high temperature homogeneity is attained by using the solid-state heating system composed of a ceramic (AlN) with high thermal conductivity comparable with that of metal aluminium. The self-diffusion coefficients D for light (1H2O) and heavy (2H2O) water are distinguishably measured at subcritical temperatures of 30-350 degrees C with intervals of 10-25 degrees C on the liquid-vapor coexisting curve and at a supercritical temperature of 400 degrees C as a function of water density between 0.071 and 0.251 gcm3. The D value obtained for 1H2O is 10%-20% smaller than those previously reported because of the absence of the convection effect. At 400 degrees C, the D value for 1H2O is increased by a factor of 3.7 as the water density is reduced from 0.251 to 0.071 gcm3. The isotope ratio D(1H2O)D(2H2O) decreases from 1.23 to approximately 1.0 as the temperature increases from 30 to 400 degrees C. The linear hydrodynamic relationship between the self-diffusion coefficient divided by the temperature and the inverse viscosity does not hold. The effective hydrodynamic radius of water is not constant but increases with the temperature elevation in subcritical water.     

Noncovalent approach to one-dimensional ion conductors: enhancement of ionic conductivities in nanostructured columnar liquid crystals

Noncovalent design of new liquid-crystalline (LC) columnar assemblies based on an ionic liquid has shown to be useful to achieve anisotropic high ionic conductivities. An equimolar mixture of an ionic liquid, 1-butyl-3-methylimidazolium bromide, and 3-[3,4,5-tri(octyloxy)benzoyloxy]propane-1,2-diol, which is partially miscible with the ionic liquid, exhibits an LC hexagonal columnar phase from -4 to 63 degrees C. This columnar supramolecular assembly forming the nanostructures shows the one-dimensional (1D) ionic conductivity of 3.9 x 10(-3) S cm(-1) at 50 degrees C along the column, which is more than 700 times higher than that of the corresponding covalent-type columnar ionic liquid, 1-methyl-3-[3,4,5-tri(octyloxy)benzyl]imidazolium bromide, which is 5.3 x 10(-6) S cm(-1) at 50 degrees C. This significant enhancement of the ionic conductivity is attributed to the increase of the mobility of the ionic part.     

17O NMR in room temperature phase of La2Mo2O9 fast oxide ionic conductor

A room temperature (17)O NMR study of La(2)Mo(2)O(9), a fast oxide ionic conductor exhibiting a phase transition at 580 degrees C between a low-temperature alpha-phase and a high-temperature beta-phase, is presented. Four partly overlapping quasi-continuous distributions of oxygen sites are evidenced from 1D magic angle spinning (MAS) and 2D triple quantum MAS NMR experiments. They can be correlated with the three oxygen sites O1, O2 and O3 of the high-temperature crystal structure. The low-temperature phase is characterized by two distributed sites of type O1, which proves that the symmetry is lower than in the cubic high-temperature phase. Two-dimensional experiments show that there is no dynamic exchange process, on the NMR time-scale, between the different oxygen sites at room temperature, which agrees well with conductivity results.     

Combined investigation of bulk diffusion and surface exchange parameters of silver catalyst coated yttrium-doped BSCF membranes

The combined effect of minor yttrium doping and silver catalyst deposition on the surface kinetics (k(chem)) and bulk diffusion (D(chem)) of BSCF (Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ)) perovskite membranes was explored using electrical conductivity relaxation (ECR) and validated using oxygen permeation measurements. Yttrium doping of BSCF to form Ba(0.5)Sr(0.5)Co(0.8)Fe(0.175)Y(0.025)O(3-δ) (BSCFY) improved both the surface exchange kinetics and the bulk diffusion by an average of 44% and 177% respectively, supporting improved oxygen permeation measurements. The deposition of a silver catalyst on BSCFY further improved the surface kinetics by 63-450% at intermediate operating temperatures (600-750 °C), and reduced the activation energy from 163 to 90 kJ mol(-1). Interestingly, these improvements did not translate into enhanced oxygen fluxes for the silver coated thicker 0.5 and 1 mm membranes, indicating that the oxygen ion transport was limited by bulk diffusion. However, oxygen permeation measurements on catalyst-coated 0.3 mm-thick membranes yielded improvements of 20-35% in the range 600-900 °C. The silver catalyst was beneficial in overcoming surface kinetic limitations for the thinner 0.3 mm BSCFY membranes, thus suggesting that the critical thickness of BSCFY membranes lies around ～0.4 mm and validating the ECR measurements.     

Dye-sensitized TiO2 solar cells using imidazolium-type ionic liquid crystal systems as effective electrolytes

A novel ionic liquid crystal (ILC) system (C(12)MImI/I(2)) with a smectic A phase used as an electrolyte for a dye-sensitized solar cell (DSSC) showed the higher short-circuit current density (J(SC)) and the higher light-to-electricity conversion efficiency than the system using the non-liquid crystalline ionic liquid (C(11)MImI/I(2)), due to the higher conductivity of ILC. To investigate charge transport properties of the electrolytes in detail, the exchange reaction-based diffusion coefficients (D(ex)) were evaluated. The larger D(ex) value of ILC supported that the higher conductivity of ILC is attributed to the enhancement of the exchange reaction between iodide species. As a result of formation of the two-dimensional electron conductive pathways organized by the localized I(3)- and I- at S(A) layers, the concentration of polyiodide species exemplified by I(m)- (m = 5, 7, ...) was higher in C(12)MImI/I(2). However, as the increment of the concentration of polyiodide species is less than that of D(ex), the contribution of a two-dimensional structure of the conductive pathway through the increase of collision frequency between iodide species was proposed. Furthermore, a quasi-solid-state ionic liquid crystal DSSC was successfully fabricated by employing a low molecular gelator. Addition of the 5.0 g/L gelator to ILC improved light-to-electricity conversion efficiency through the increase of J(SC) due to the enhancement of the conductivity in C(12)MImI/I(2)-gel.     

Influence of plasticizer type on the properties of polymer electrolytes based on chitosan

Polymer electrolytes were obtained by the casting technique from a solution containing chitosan, hydrochloric acid, and plasticizer such as glycerol, ethylene glycol, and sorbitol. The transparent membranes with good ionic conductivity properties were characterized by impedance and UV-vis spectroscopies, thermal analysis (DSC), and X-ray diffraction. The best ionic conductivity values of 9.5 x 10(-4) S cm(-1) at room temperature and 2.5 x 10(-3) S cm(-1) at 80 degrees C were obtained for the sample containing 59 wt% of glycerol and an equimolar amount of HCl with respect to NH2 groups in chitosan. The temperature dependence of the ionic conductivity exhibits an Arrhenius behavior with activation energy of 16.6 kJ mol(-1). The thermal analysis indicates that both glass transition temperature (-87 degrees C) and crystallinity are low for this electrolyte. The samples with 13 wt% of LiCF3SO3 showed that the ionic conductivity values of 2.2 x 10(-5) S cm(-1) at room temperature and 4 x 10(-4) S cm(-1) at 80 degrees C are predominantly amorphous and showed a low glass transition temperature of about -73 degrees C.     

Studies on oxygen chemical surface exchange and electrical conduction in thin film nanostructured titania at high temperatures and varying oxygen pressure

We report on oxygen surface exchange studies in ～450-nm-thick nanocrystalline titania films with an average grain size of ～13 nm by electrical conductivity relaxation along with the conductivity measurements at varying temperatures and oxygen partial pressures (pO(2)s). By electrochemical impedance spectroscopy technique, the high temperature conductivity was measured in the pO(2) range from ～10(-16) to ～10(-6) Pa at temperatures from 973 to 1223 K and activation energy, ΔE(a), for conduction was estimated as ～3.23 eV at pO(2) ～10(-11) Pa. Under reducing atmosphere (pO(2) < 10(-6) Pa), two distinct n-type conduction regimes were observed and corresponding predominant defects are discussed while, at high pO(2) regime (pO(2) >10(-6) Pa), ionic conduction appears dominant leading to a conductivity plateau. The surface relaxation was observed to have two independent time constants likely originating from microstructural effects. The surface exchange coefficients are measured as ～10(-8)-10(-7) m∕s and ～10(-9)-10(-8) m∕s for each contribution with ΔE(a)s of 2.79 and 1.82 eV, respectively, without much pO(2) dependence across several orders of pO(2) range of ～10(-16)-10(-6) Pa in the temperature range between 973 and 1223 K. The results are of potential relevance to understanding the near-surface chemical phenomena in nanocrystalline titania which is of great interest for energy and environmental studies.     

Apparent solubility of hydroxyapatite in aqueous medium and its influence on the morphology of nanocrystallites with precipitation temperature

Two differing wet-chemical synthesis routes, Ca(OH)2 + H3PO4 and CaCl2 + Na3PO4/NaOH, were used to prepare hydroxyapatite (HA) at various temperatures ranging from 30 to 95 degrees C. The electrical conductivity of the solution was measured at regular intervals of time during H3PO4 and Na3PO4 addition to the suspension/solution containing Ca2+ ions. The rate of change of conductivity is used to note the end point of the reaction. X-ray diffraction of the dried, precipitated particles revealed HA as the predominant phase, and the FTIR spectroscopy studies indicated the presence of CO3(2-) groups which substituted PO4(3-) groups in the HA lattice (B-type). FESEM observations revealed that the aspect ratio of the particles decreased with increasing precipitation reaction temperature in one system [Ca(OH)2 + H3PO4] and in the other system it increased with increasing temperature. The changes in the morphology with temperature were analyzed through conductivity measurements and the thermochemical properties of the reaction systems. Conductivity measurements showed that the concentration of dissolved ions at the end point of the reaction between Ca(OH)2 and H3PO4 increased, indicating an increased apparent solubility of HA with increasing temperature, whereas the end-point conductivity did not increase noticeably in the other reaction system.     

Oxygen surface exchange kinetics of SrTi(1-x)Fe(x)O(3-δ) mixed conducting oxides

The oxygen surface exchange kinetics of mixed conducting perovskite oxides SrTi(1-x)Fe(x)O(3-δ) (x = 0, 0.01, 0.05, 0.35, 0.5) has been investigated as a function of temperature and oxygen partial pressure using the pulse-response (18)O-(16)O isotope exchange (PIE) technique. Arrhenius activation energies range from 140 kJ mol(-1) for x = 0 to 86 kJ mol(-1) for x = 0.5. Extrapolating the temperature dependence to the intermediate temperature range, 500-600 °C, indicates that the rate of oxygen exchange, in air, increases with increasing iron mole fraction, but saturates at the highest iron mole fraction for the given series. The observed behavior is concomitant with corresponding increases in both electronic and ionic conductivity with increasing x in SrTi(1-x)Fe(x)O(3-δ). Including literature data of related perovskite-type oxides Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ), La(0.6)Sr(0.4)Co(0.2)Fe(0.8)O(3-δ), La(0.6)Sr(0.4)CoO(3-δ), and Sm(0.5)Sr(0.5)CoO(3-δ), a linear relationship is observed in the log-log plot between oxygen exchange rate and oxide ionic conductivity with a slope fairly close to unity, suggesting that it is the magnitude of the oxide ionic conductivity that governs the rate of oxygen exchange in these solids. The distribution of oxygen isotopomers ((16)O(2), (16)O(18)O, (18)O(2)) in the effluent pulse can be interpreted on the basis of a two-step exchange mechanism for the isotopic exchange reaction. Accordingly, the observed power law dependence of the overall surface exchange rate on oxygen partial pressure turns out to be an apparent one, depending on the relative rates of both steps involved in the adopted two-step scheme. Supplementary research is, however, required to elucidate which of the two possible reaction schemes better reflects the actual kinetics of oxygen surface exchange on SrTi(1-x)Fe(x)O(3-δ).     

Nanocomposite ion gels based on silica nanoparticles and an ionic liquid: ionic transport, viscoelastic properties, and microstructure

The dispersion of silica nanoparticles made an ionic liquid, 1-ethyl-3-methyl imidazolium bis(trifluoromethanesulfonyl)amide ([C(2)mim][NTf(2)]), gelled even by the addition of 2-3 wt %, due to the formation of interconnected particulate silica networks in [C(2)mim][NTf(2)]. The ionic transport and viscoelastic properties of these nanocomposite ion gels were investigated in relation to the microstructure. Despite their solid-like behavior, the nanocomposite ion gels exhibited a high ionic conductivity of approximately 10(-2) S cm(-1) at 30 degrees C, which is comparable to that of neat [C(2)mim][NTf(2)]. Intriguing viscoelastic responses, such as shear-thinning and shear-induced sol-gel transitions, were found in all of the nanocomposite ion gels. By adjusting the silica concentration, the elastic modulus ( G') could be precisely controlled in a range of more than 3 orders of magnitude and reached approximately 10(6) Pa without a considerable decrease in the ionic conductivity; the characteristic viscoelastic response was also maintained. For the aggregation mechanism in [C 2 mim][NTf(2)], the reaction-limited cluster aggregation (RLCA) model was proposed by rheology and light scattering measurements.     

Quaternary ammonium room-temperature ionic liquid including an oxygen atom in side chain/lithium salt binary electrolytes: ionic conductivity and 1H, 7Li, and 19F NMR studies on diffusion coefficients and local motions

A room-temperature ionic liquid (RTIL) of a quaternary ammonium cation having an ether chain, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethylsulfonyl)amide (DEME-TFSA), is a candidate for use as an electrolyte of lithium secondary batteries. In this study, the electrochemical ionic conductivity, sigma, of the neat DEME-TFSA and DEME-TFSA-Li doped with five different concentrations of lithium salt (LiTFSA) was measured and correlated with NMR measurements of the diffusion coefficients D and the spin-lattice relaxation times T1 of the individual components DEME (1H), TFSA (19F), and lithium ion (7Li). The ion conduction of charged ions can be activated with less thermal energy than ion diffusion which contains a contribution from paired ions in DEME-TFSA. In the doped DEME-TFSA-Li samples, the sigma and D values decreased with increasing salt concentration, and within the same sample generally DLi相似文献   

A liquid derivative of 12-tungstophosphoric acid with unusually high conductivity

Surface functionalization of the solid heteropolyacid H3PW12O40 with a bulky PEG-containing quaternary ammonium cation through partial proton exchange leads to a polyoxometalate-based liquid salt with high-temperature proton conductivity ( approximately 10-3 S cm-1 at 140 degrees C) under dry conditions. The proton conductivity of the liquid salt is 4 orders of magnitude higher than that of the solid analogue under identical conditions and shows super ionic behavior as defined by Walden plot.     

Novel polysilsesquioxane-I-/I3- ionic electrolyte for dye-sensitized photoelectrochemical cells

A new sol-gel precursor, based on 1-methyl-3-[3-(trimethoxy-lambda(4)-silyl)propyl]imidazolium iodide (MTMSPI(+)I(-)), was synthesized and investigated as a potential novel quasi-solid-state ionic liquid redox electrolyte for dye-sensitized photoelectrochemical (DSPEC) cells of the Graetzel type. MTMSPI(+)I(-) was hydrolyzed with acidified water, and the reaction products of the sol-gel condensation reactions were assessed with the help of (29)Si NMR and infrared spectroscopic techniques. Results of time-dependent analyses showed the formation of a positively charged polyhedral cubelike silsesquioxane species, which still contained a small amount of silanol end groups that were removed after heating at 200 degrees C. After cooling, the material formed was a tough, yellowish, and transparent solid, consisting mainly of ladderlike polysilsesquioxane species. The specific conductivity (sigma) of the nonhydrolyzed MTMSPI(+)I(-) (no I(2)) was 0.23 mS/cm, while the activation energy (E(a)), determined from the Vogel-Tamman-Fulcher (VTF) relation, was 0.29 kJ/mol. After 56 days of aging the sigma value of the hydrolyzed MTMSPI(+)I(-) dropped to 0.11 mS/cm but the viscosity had already increased to 7500 Pa.s after 17 days, demonstrating that a quasi solid state was attained. Apparent diffusion coefficients (D(app)) of I(-) and I(3)(-) obtained from the voltammetric measurements were approximately 10(-7) cm(2)/s and decreased to approximately 10(-8) cm(2)/s after 15 days of sol aging. Time-dependent vibrational spectra, which served in assessing the hydrolysis and condensation reactions of MTMSPI(+)I(-), were measured with the help of the attenuated total reflectance (ATR) IR spectroscopic technique. The results revealed that, in the course of condensation of sols, the refractive index of the modes attributed to the polysilsesquioxane species exhibited strong dispersion, which led to a shift of the vibrational band position in the experimental ATR spectra. This effect accompanies the sol-to-gel transformations and has not yet been considered as a possible error in analysis of the ATR spectra of sols and gels. The calculation procedure for obtaining the corresponding transmission spectra is briefly outlined, and the results are applied in this work.