Composite solid electrolytes based on n-methyl-n-butyl-piperidinium tetrafluoroborate [(CH3)(C4H9)C5H10N]BF4–A (where A is γ-Al2O3, SiO2) were synthesized and their thermal and electrically conductive properties have been studied. It was found that the conductivity of the [C10H22N]BF4–Al2O3 composites passes through a maximum at x~0.9 and reaches a value of 4.6·10-4 S/cm at 130оC for the 0.1[C10H22N]BF4–0.9Al2O3 composite. The absence of a thermal effect at the melting temperature of the ionic salt, which indicates a high ionic conductivity, indicates that at x ≥ 0.9, n-methyl-n-butyl-piperidinium tetrafluoroborate is in the amorphous state and ion transfer occurs along the ionic salt/oxide phase boundary. In the case of [C10H22N]BF4 – SiO2 composites, the effect of a heterogeneous dopant on ion transport is less significant and the conductivity is due to the ionic salt of the additive present in the pores.

Министерство науки и высшего образования Российской Федерации Российское химическое общество им.Д.И.Менделеева Секция по химической термодинамике и термохимии Научного совета РАН по физической химии Сибирское Отделение Российской Академии Наук Институт неорганической химии им.А.В.Николаева СО РАН

Nanocomposite solid electrolytes (C4H9)4NBF4–MIL-101(Cr) based on pure components without any other additives were prepared and their structure and electrical properties were investigated as a function of temperature and concentration of the metal-organic framework MIL-101(Cr). According to the data of thermal analysis, the heat effect due to the melting of the salt in the composites strongly decreases and tends to zero at a molar fraction of MIL-101(Cr) x ≥ 0.34. This effect is assumed to be caused by the amorphization of the salt in the composites which is practically complete at high content of MIL-101(Cr). The dependence of the melting enthalpy on the molar or mass fraction of MIL-101(Cr) may be explained by filling of MIL-101(Cr) pores with the salt, provided that the salt residing outside the pores is crystalline, whereas the salt located inside the pores is amorphous. In this case, at some fraction of the MIL-101(Cr), x = xmax, all the salt will be located inside the pores, and the concentration of the salt occurring in an amorphous state reaches a maximum. At x < xmax there is a linear dependence between melting enthalpy and molar (or mass) fraction from which allows one can determine xmax and wmax values from experimental data. From these data, the volume of accessible pores was estimated as Vpore = 0.92 cm3/g corresponding to 73% of the total pore volume determined by BET adsorption method. The thermal properties fairly correlate with the X-ray diffraction data. Reflections on X-ray diffraction patterns of the composites attributed to (C4H9)4NBF4 strongly decrease with the concentration of MIL-101(Cr) and at the concentration x ≥ 0.283 practically no reflections of the salt are observed on the X-ray patterns. The electrical properties of the composites were investigated. It was shown that the concentration dependence of conductivity has a maximum at the concentration close to xmax value determined from the thermal analysis data. At x > xmax temperature dependences of conductivity are not linear in Arrhenius coordinates, no sudden conductivity change is observed due to the melting of the salt. Such conductivity behaviour is typical for amorphous electrolytes. Quantitative analysis of the concentration dependence of conductivity was done using the pore filling model and the mixing equations proposed earlier for two-phase composites. Theoretical curves obtained using the mixing equations satisfactorily fit the experimental data. The maximum value of ionic conductivity, 5∙10−4 S/cm at 135 °C, obtained for the composite 0.675(C4H9)4NBF4–0.325MIL-101(Cr) is rather high assuming that BF4− anions are the most probable charge carriers.

Composite solid electrolytes (1 – х )LiTi 2 (PO 4 ) 3 – x LiClO 4 are synthesized and their conducting properties are studied. Heterogeneous doping of LiTi 2 (PO 4 ) 3 with lithium perchlorate LiClO 4 leads to a considerable increase of ionic conductivity and a decrease of activation energy as compared to the pure compound, which was not subjected to the pre-sintering. The conductivity of the composites reaches 6.8 × 10 –6 S/cm at 100°C and 3.4 × 10 –4 S/cm at 200°C with an activation energy of 0.62 eV.

Composite solid electrolytes (1 – х)LiTi2(PO4)3–xLiClO4 are synthesized and their conducting properties are studied. Heterogeneous doping of LiTi2(PO4)3 with lithium perchlorate LiClO4 leads to a considerable increase of ionic conductivity and a decrease of activation energy as compared to the pure compound, which was not subjected to the pre-sintering. The conductivity of the composites reaches 6.8 × 10–6 S/cm at 100°C and 3.4 × 10–4 S/cm at 200°C with an activation energy of 0.62 eV.

Novel and stable to carbonization nanocomposite materials based upon Pr2−xNiO4+δ, Pr1−xSmxNi1−yCoyO3−δ and YDC were synthesized via Pechini route and ultrasonic dispersion, and were sintered using conventional and advanced (microwave, e-beam) techniques. Their real/nano structure and transport properties were characterized by sophisticated methods. Nanocomposites have high oxygen mobility due to cooperative mechanism of migration for Pr2−xNiO4+δ and fast channel of diffusion for nanocomposites due to Pr cations' incorporation into YDC. Power density values of single SOFCs were up to 0.5 W/cm2 at 700 °C, being comparable with that for state-of-the-art cathodes. For oxygen separation membranes, high and stable performance was demonstrated.

AbstractThe structural and dynamic properties of a tetrafluoroborate ion in n -Bu_4NBF_4 organic salt at different temperatures and phase states were studied by oscillation spectroscopy methods. The results of calculations of the energy and relaxation parameters have shown that in the plastic phase, a $${\text{BF}}_{4}^{ - }$$ ion is characterized by a low reorientation energy as compared with that of the crystalline phase.

Ceramic solid proton electrolytes La 0,99 Ca 0,01 NbO 4 , Nd 5,5 WO 11,25- δ и Nd 5,5 W 0,5 Mo 0.5 O 11,25- δ were synthesized and their proton conductivity was measured in the temperature range of 300-650 оС in an atmosphere of dry and humid air. Solid electrolytes are shown to have a high proton conductivity ~ 10 -4 S/cm at 500 оС. Dense metal-ceramic composites containing phases of metal Ni 0,5 Cu 0,5 and oxides Nd 5.5 WO 11.25 or Nd 5.5 W 0.5 Mo 0.5 O 11.25- δ with the typical total conductivity of metals were obtained using hot pressing technique an argon atmosphere. The problem arises with an experimental determination of the ionic (in this case proton) conductivity contribution to the overall conductivity of the material comprises when studying the metal-ceramic materials properties. The proton conductivity values can be estimated from the results of studying the hydrogen permeability of membranes and the diffusion of hydrogen; however, these methods are rather complicated in instrumentation. Therefore the use of relatively simple and accessible electrical measurement methods to solve this problem is very relevant. In this paper, the partial proton conductivity of the composite materials mentioned above was first measured using a 4-electrode cell with ion probes made of a ceramic proton conductor La 0,99 Ca 0,01 NbO 4 in an atmosphere of moist hydrogen and at the temperature range of 300-650 оC. In the low temperature region, the partial proton conductivity values measured in the 4-electrode cell are in good agreement with those obtained by standard complex impedance analysis for the pure ceramics not containing metal. In high temperature region, the values obtained by two independent techniques differ. This can be explained by the contribution of the electrochemical reaction proceeding at the interface between the ion probe and the metal phases and accompanied by the dissolution of atomic hydrogen in the metal. In general, the measured value of the ionic conductivity can be either underestimated or overestimated in comparison with the real one, depending on the rate of chemical reactions occurring at the electrodes. Nevertheless, in a limited temperature range, the use of four-electrode measurements with ionic (proton) probes allows one to obtain correct results.

The structural and dynamic properties of a tetrafluoroborate ion in n-Bu4NBF4 organic salt at different temperatures and phase states were studied by oscillation spectroscopy methods. The results of calculations of the energy and relaxation parameters have shown that in the plastic phase, a \({\text{BF}}_{4}^{ - }\) ion is characterized by a low reorientation energy as compared with that of the crystalline phase.

Composite solid electrolytes were synthesized from the organic salt dimethylammonium chloride (1–x)C2H8NCl–xAl2O3. Their physicochemical properties were studied. In the starting C2H8NCl salt, there is a phase transition at 39°C accompanied by an increase in conductivity by two orders of magnitude. The conductivity of the high-temperature phase is 9.3 × 10–6 S/cm at 160°C. A differential scanning calorimetry study showed that the salt in the composites spreads over the oxide surface and at x > 0.6 the salt melting enthalpy decreases to zero. The conductivity of the resulting composites was studied by impedance spectroscopy. It was shown that heterogeneous doping leads to a sharp increase in ion conductivity to 7.0 × 10–3 S/cm at 160°C and a decrease in the activation energy to 0.55 eV.

Ionic mobility and electrical conductivity of solid solutions with fluorite structure, obtained with solid-state approach in PbF2–SbF3 and PbF2–SnF2–SbF3 systems, are studied by 19F NMR and electrochemical impedance spectroscopy methods. The 19F NMR spectra parameters, types of ion motions in the fluoride sublattice, and the ionic conductivity magnitude are shown to be determined by the temperature and fluoride concentration in the solid solutions. The solid solution specific conductivity in the PbF2–SbF3 and PbF2–SnF2–SbF3 systems at 420–450 K is as high as ~10–2 S/cm, which allows accounting the solid solutions as a base for preparation of functional materials.

The ion conductivity of the salts [(C4H9)4N]BF4 and [(C4H9)4N]Br was studied in vacuum at temperatures from room temperature to 190 and 135°C, respectively. The salts have phase transitions to disordered high-temperature phases accompanied by an increase in conductivity. [(C4H9)4N]Br has higher conductivity than [(C4H9)4N]BF4. As the conductivity decreases with the increasing size of the anion, the BF4 – and Br– anions are the most probable current carriers in the salts.

The ion mobility and conductivity in solid solutions with the fluorite structure (100–x)KBiF4 + xZrF4, where x = 2.5–15 mol %, is studied by the methods of differential scanning calorimetry (DSC), X-ray diffraction (XRD), and 19F NMR. The character and type of ion transport in the fluorite sublattice of solid solutions are studied as well as the temperature intervals in which it is observed (150–570 K). For solid solutions containing 5 and 10 mol % ZrF4, the fluorine ion diffusion coefficient is assessed. It is found that the conductivity in the solid solution systematically decreases as the content of zirconium tetrafluoride in the sample decreases, which is probably due to the formation of strongly bound complexes formed by interstitial fluoride ions with zirconium cations. The presence of the high ionic conductivity in the tested solid solutions (from ~10–3 to 10–2 S/cm) makes this material a good candidate for preparation of materials with the high ion-conducting properties.

For powders of oxide-ion conductors based on Al/Fe- doped lanthanum silicates as well as Sc+Ce-doped zirconia, the temperature –programmed exchange with C18O2 in the SSITKA mode was applied for estimation of the oxygen self-diffusion coefficients Do. Comparison with results obtained for dense ceramics of these electrolytes using SIMS isotope profiling and conductivity measurements demonstrated a reasonable agreement for powders sintered at high temperatures, thus providing required verification of C18O2 SSITKA approach. For powders calcined at moderate temperatures much lower values of DO were obtained thus suggesting a strong negative effect of inhomogeneity of dopants spatial distribution on the oxygen mobility.