Layered perovskites Sr1+xLa1-xAlO4-0.5x (x = 0.1, 0.2) with the Ruddlesden-Popper structure were synthesized by the combustion method (glycine-nitrate soft-chemistry technique) and investigated as potential oxide ion conductors for intermediate-temperature devices for electrochemical applications. X-ray diffraction analysis confirmed the formation of single-phase materials with tetragonal symmetry (space group I4/mmm). The introduction of Sr2+ cation in the place of La3+ leads to the creation of oxygen vacancies and a significant increase in ionic conductivity. At 600 °C, the total conductivity increased by factors of 270 and 40 for x = 0.1 and 0.2, respectively, compared to the undoped sample SrLaAlO4. The activation energy for oxygen ion transport decreased from 1.51 eV for the parent compound to 0.84 eV for the doped phases. The optimal Sr2+ doping level was determined to be 10 mol%, which provides the best balance between structural parameters (unit cell volume and free cell volume) and oxygen vacancy concentration. The bulk oxygen-ion conductivity at 700 °C for the sample Sr1.1La0.9AlO3.95 reaches 10-3 S cm⁻¹. All the studied phases are stable over a wide range of PO2(10-20 ‒0.68 atm) at 400‒900 oC. The present result endorses that the RP compounds based on aluminates are low-cost promising candidates for electrochemical devices.

Hexagonal perovskites with intergrowth structure are novel and promising class of protonic conductors. The development of this class of materials makes it possible to develop proton-conducting materials for intermediate temperatures (300-600 degrees C) electrochemical devices including fuel cells. In this work, non-metal doping strategy was first applied to this class of materials. New hexagonal perovskite Ba7In6Al1.9P0.1O19.1 was obtained and investigated as a proton conductor. Ba7In6Al1.9P0.1O19.1 showed the ability to water uptake and exhibited significantly higher values of hydration degree (1.31 mol H2O), than parent compound (0.41 mol H2O). The high hydration ability is explained by the increase in the unit cell volume, and, consequently, the increase in sufficient space for the incorporation of OH- -groups in hexagonal layer. The investigation of transport properties showed that in dry atmosphere (pH(2)O = 3.5.10(-5) atm) the Ba7I-n(6)Al(1.9)P(0.1)O(19.1) compound was a mixed conductor. Doping made it possible to increase the oxygen-ion conductivity by 0.25 orders of magnitude. In wet air (pH(2)O = 2.10(-2) atm) below similar to 500 degrees C the conductivity was the predominantly protonic. Proton conductivity increased by 0.5 orders of magnitude compared to the undoped phase as a result of the increase in proton concentration. Thus, investigated phase Ba7In6Al1.9P0.1O19.1 is a promising electrolyte for intermediate-temperature electrochemical devices. The strategy of phosphate oxyanion doping is a successful method for optimizing transport properties of hexagonal perovskite with intergrowth structure.

Hexagonal perovskites with a block structure are a promising new class of proton conductors. Such compounds are capable of incorporating protons without doping with an acceptor impurity, which is used for classical perovskites. However, the strategy for optimizing the transport properties of such phases by introducing any dopants is poorly understood. In this work, the prospect of introducing an isovalent gallium dopant into the aluminum positions of the hexagonal perovskite Ba7In6Al2O19 is shown. The effect of Ga3+ substitution on the structure, proton concentration, hydration thermodynamics and electrical conductivity has been studied. The phase Ba7In6Al1.9Ga0.1O19 with a hexagonal perovskite structure was synthesized by the modified Pechini method. The introduction of gallium was accompanied by an increase in lattice parameters. The investigated phase Ba7In6Al1.9Ga0.1O19 was capable of hydration and incorporate up to 1.53 mol H2O in comparison with 0.41 mol H2O for the parent phase. This result is consistent with the general trend for block-layered structures of increasing proton concentration with increasing unit cell volume and as a consequence, an increase in open space around the Ba2+-sites for the placement of OH-- groups. Proton conductivity dominated below 500 degrees C in wet (pH2O =2 x10-2 atm) conditions. Doping results in an increase in proton conductivity by approximately one order of magnitude and significantly increases the proton transport numbers, which is a consequence of the increase in the proton concentration. The activation energy of proton conductivity decreases to 0.38 eV compared to 0.47 eV for the parent phase, which is a favorable factor for maintaining acceptable values of proton conductivity over a wide temperature range.

The thermal and electric properties of the Y3+-doped Ba7In5.9Y0.1Al2O19 phase with the hexagonal perovskite structure (a = 5.935(7) Å, c = 37.736(8) Å) are studied. It is shown that this phase can incorporate protons and exhibit protonic conduction. Upon addition of an isovalent dopant, yttrium, the concentration of protons increases (up to the limiting value for Ba7In5.9Y0.1Al2O19·0.55H2O), as a result of the increase in the unit cell volume and, correspondingly, in the free space for accommodating OH– groups in the oxygen-deficient block containing coordination-unsaturated polyhedrons [BaO9]. The isovalent doping increases the oxygen-ionic conductivity due to an increase in interatomic distances and a decrease in the activation energy of migration. In a humid atmosphere (pH2O = 1.92 × 10−2 atm), the Ba7In5.9Y0.1Al2O19 phase exhibits the higher values of protonic conductivity as compared with the matrix compound Ba7In6Al2O19 and below 500°C is characterized by the predominant proton transport both in air and in a wide pO2 region (10–18–0.21 atm).

The search for sodium-containing materials with high ionic conductivity is crucial for the development of sodium-ion battery technologies. This article presents the results of comprehensive experimental and theoretical studies of the novel triple molybdate Na1-xMg1-xIn1+x(MoO4)3 (x = 0.1-0.5) obtained by solid-state synthesis. The crystal structure was examined by X-ray diffraction and assigned to the NASICON type (space group R3¯c, Z = 6). The results of impedance and 23Na NMR spectroscopy, as well as BVSE and DFT calculations, revealed the occurrence of rather fast translational diffusion of sodium atoms with an activation energy, Ea ≈ 0.7 eV.

Proton-conducting oxide electrolytes can be used in protonic ceramic electrochemical cells (PCECs) applied for power generation and sustainable hydrogen production (Norby, 2001) [1]. For successful using PCECs, their long-term stability and high performance characteristics are required, accordingly, protonic electrolyte must have a wide range of functional characteristics (Hossain et al., 2017) [2]. Besides, the lowering the PCECs operating temperature can facilitate their scale-up and commercialization. However, achieving high proton conductivity at low operating temperatures is a long-standing challenge. Here, for the first time, we show the discovering a high proton conduction with low activation energy in hexagonal perovskite Ba7Sc6Al2O19 with cation- and oxygen-deficient layers. The sample shows high bulk proton conductivity of similar to 5.10(-3) S cm(-1) at 300-500 degrees C with very low activation energy 0.12 eV, and high chemical stability (towards to H-2, CO2 and electrode materials). These results demonstrate that new super-protonic Ba7Sc6Al2O19 is a promising proton conductor for the applications both in intermediate and low-temperature (<400 degrees C) solid-oxide fuel cells.

Widespread commercialization of sodium-ion batteries (SIB) is limited by the shortcomings of existing electrode materials, so the search and testing of various sodium compounds suitable for SIB are relevant. This paper presents the results of a study of the sodium diffusion mechanisms in quasi-layered oxides Na1-xV1-xMo1+xO6, which are potentially promising for applications for SIB. A simple synthesis procedure has been developed, which makes it possible to obtain compounds in a wide range of compositions up to x = 0.2. To elucidate the mechanisms of sodium diffusion, we applied a comprehensive approach that combines material characterization at the “macro” (XRD, impedance spectroscopy) and “atomic-scale” levels (NMR, ab-initio calculations). Our results reveal rather fast sodium dynamics: Ionic conductivity reaches the values of 10–3 S/cm at T > 730 K. It has been found moreover that the diffusion mechanism changes with increasing temperature. At T < 625 K, sodium motion occurs mainly along the crystallographic b axis due to atomic jumps with the shortest jump length ≈ 3.6 Å and activation energy Ea 1 eV. With increasing temperature, another type of jumps along a axis (in the ab plane) with a jump length of ≈ 5 Å and a barrier value of 2 eV is also activated.

The novel phase Ba7In5.9Zn0.1Al2O18.95 with hexagonal perovskite structure was obtained by solid-state technique. The substitution of In3+ by the Zn2+ leads to the expansion of the lattice parameters and cell volume. It was established that the investigated sample is capable of water incorporation from the gas phase; the degree of hydration reaches 1.42 mol H2O, which is significantly higher than that for the undoped phase (0.41 mol H2O). This is a result of the expansion of the hexagonal layer that facilitates the placement of OH–-groups. The oxide-ion and proton conductivities for the doped Ba7In5.9Zn0.1Al2O18.95 sample were higher than those for the undoped composition, Ba7In6Al2O19, by 0.50 and 0.75 orders of magnitude (500 °C), respectively. The new phase Ba7In5.9Zn0.1Al2O18.95 demonstrates the predominant protonic conductivity at Т ≤ 500 °C and pH2O = 1.93·10−2 atm.

K x Ln 5− x Mo 3 O 16− y F y (Ln = La, Pr, Nd) compositions were first synthesized. The conductive properties have been widely studied using a combination of theoretical and experimental approaches. The total conductivity reaches ∼10 −2 S cm −1 at 800 °C.

The solid solution Ba5In2-xYxAl2ZrO13 (0 <& khcy;<0.50)with hexagonal structure (space group P 6 3 / mmc ) was prepared by the solid-state reaction method. The effects of isovalent Y3+-substitution on the structure, hydration, bandgap and transport properties have been investigated. The introduction of yttrium was accompanied by lattice expansion, which led to an increase in the concentration of protons during hydration. The doping did not lead to a significant increase in oxygen-ion conductivity since there was no change in oxygen stoichiometry. At the same time, doping led to an increase in ionic transport numbers due to a decrease in hole conductivity. Proton conductivity contribution and the values of proton conductivity increase with the increase in yttrium concentration. The phases with yttrium content x > 0.2 were predominant proton conductors at the temperature below 600 degrees & Scy; degrees & Scy; under wet air.

A CO2-stable, 2-stable, easily sintered proton-conducting oxide electrolytes based on solid solution Ba 7 In 6 Al 2- x Zn x O 19-0.5 x with hexagonal structure has been synthesized for the first time. Within the homogeneity region (0 <= x <= 0.10), there is an increase in unit cell parameters, cell volumes and free cell volumes. The addition of Zn2+ 2+ markedly improved the sinterability of the material. The relative density of the ceramics of the doped samples reached 95 % at lower sintering temperatures than the parent phase. The electrical conductivity was studied using electrochemical impedance spectroscopy. Upon doping the oxygen-ion conductivity increased by 0.25 orders of magnitude at 800 degrees C. Proton transport was predominant below 500 degrees C for a wet atmosphere (pH2O 2 O = 1.92 center dot 10-2 atm). The investigated phases Ba 7 In 6 Al 2- x Zn x O 19-0.5 x are capable of hydration and incorporate up to 1.45 mol H2O 2 O vs 0.41 mol H2O 2 O for the parent phase. The studied phases exhibit chemical resistance to CO2 2 under heat treatment at 600 degrees C. It was shown that solid solution Ba 7 In 6 Al 2- x Zn x O 19-0.5 x is a promising electrolyte material for intermediate-temperature fuel cells.

Composite materials (1-f)SrWO4–fSiO2 and (1–f)BaWO4–fSiO2, where f is the volume fraction of the dispersed SiO2 additive, were prepared by the solid-phase method. The resulting composites were studied by XPA, TG-DSC, SEM-EDA. The electrical conductivity of the composites was measured by the electrochemical impedance method as a function of temperature, oxygen partial pressure in the gas phase, and composition. To estimate the contribution of ionic conductivity, the sum of ionic transfer numbers was measured by the EMF method. It has been shown that the addition of 20–25 vol % nano-SiO2 to low-conductivity oxygen-ion conductors SrWO4 and BaWO4 leads to an increase in the ionic conductivity of composites based on them by two orders of magnitude and by 12 times, respectively. The increase in conductivity in the systems under study is explained by the additional contribution of interfacial boundaries formed between the MeWO4 matrix and dispersoid nanoparticles. The mixing rule [1] was used to calculate the electrical conductivity of (1-f)SrWO4–fSiO2 and (1-f)BaWO4–fSiO2 composites depending on the SiO2 content. The calculated concentration dependences of the conductivity obtained are in satisfactory agreement with the experimental results.

A complex oxide Ba 5 In 1.9 Y 0.1 Al 2 ZrO 13 with hexagonal perovskite structure ( a = 5.971(4) Å, с = 24.012(1) Å) is prepared for the first time. The phase is found to dissociative-absorb water from gas phase, the degree of hydration being as high as 0.39 mol Н 2 О. It was found by using IR-spectroscopy that protons are present therein as energetically nonequivalent ОН – -groups involved in hydrogen bonds of diverse strength. Isovalent yttrium-doping of the Ba 5 In 2 Al 2 ZrO 13 phase is shown not to lead to any valuable change in the oxygen-ion-conductivity as compared with the Ba 5 In 2.1 Al 2 Zr 0.9 O 12.95 acceptor doping that allows increasing the oxygen-ion-conductivity by a factor of 1.3. Both types of doping lead to increase in the proton conductivity and, as a corollary to this, an increase in the proton concentration. For these phases the degree of hydration depends on the cell parameters, hence, is determined by space availability for ОН – -groups in the barium coordination. Proton transport dominates in the Ba 5 In 2 Al 2 ZrO 13 , Ba 5 In 2.1 Al 2 Zr 0.9 O 12.95 , and Ba 5 In 1.9 Y 0.1 Al 2 ZrO 13 phases below 600 о С in humid atmosphere ( p H 2 О = 1.92 × 10 –2 atm).

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

The work is devoted to the adaptation of a soft and convenient method for the synthesis of a microstructured titanium-phosphorus double oxide (TPDO). Synthesis is based on the use of a stable water-soluble complex of titanium with mandelic acid. Resulting materials showed excellent structural consistency and narrow size distribution. Hydrothermal treatment conditions have been studied to determine its effect on morphology and revealed a complex effect of the temperature on the size of the microstructure. High dihydrophosphate content in the TPDO suggested them as potent proton conductors. Analysis of conductivity of as-obtained and calcined samples confirmed the assumption of their different hydration degree, which may be controlled with synthesis conditions.

Development of the technologies for energy storage and conversion requires a search for compounds with high diffusion of alkali and alkaline-earth ions. Here, we present the results of comprehensive studies, including synthesis, powder X-ray diffraction, experiments on impedance and Na-23 NMR spectroscopy, as well as ab initio calculations, which were carried out to explore the sodium diffusion in scheelite-like Na5M(MoO4)(4) with M = Y, La, Bi, and in related solid solutions Na5-xM1-xZrx(MoO4)(4) (0.05 <= x <= 0.1), which were synthesized for the first time. Our investigations reveal that the Na-ion mobility increases in the sequence Y -> La -> Bi and with growing x. For Na4.9Bi0.9Zr0.1(MoO4)(4) the highest ion conductivity was found: similar to 10(-4) S/cm at T = 450 degrees C, which is comparable to that of the NASICON-type molybdates. From the temperature variations of the Na-23 NMR spectra and DFT calculations, the mechanism of sodium-ion diffusion was established at the atomic-scale level.

Composite materials (1 – f)SrWO4–fSiO2 and (1 – f)BaWO4–fSiO2, where f is the volume fraction of the disperse additive SiO2, are prepared by the solid-phase method and studied by the XRD, TG-DSC, and SEM-EDX methods. The conductivity of composites is measured by the electrochemical impedance method as a function of temperature, partial pressure of oxygen in the gas phase, and composition. The contribution of the ionic conductivity was assessed based on the sum of transport numbers of ions measured by the EMF method. It is shown that the addition of 20–25 vol

A complex oxide Ba5In1.9Y0.1Al2ZrO13 with hexagonal perovskite structure (a = 5.971(4) Å, с = 24.012(1) Å) is prepared for the first time. The phase is found to dissociative-absorb water from gas phase, the degree of hydration being as high as 0.39 mol Н2О. It was found by using IR-spectroscopy that protons are present therein as energetically nonequivalent ОН–-groups involved in hydrogen bonds of diverse strength. Isovalent yttrium-doping of the Ba5In2Al2ZrO13 phase is shown not to lead to any valuable change in the oxygen-ion-conductivity as compared with the Ba5In2.1Al2Zr0.9O12.95 acceptor doping that allows increasing the oxygen-ion-conductivity by a factor of 1.3. Both types of doping lead to increase in the proton conductivity and, as a corollary to this, an increase in the proton concentration. For these phases the degree of hydration depends on the cell parameters, hence, is determined by space availability for ОН–-groups in the barium coordination. Proton transport dominates in the Ba5In2Al2ZrO13, Ba5In2.1Al2Zr0.9O12.95, and Ba5In1.9Y0.1Al2ZrO13 phases below 600оС in humid atmosphere (pH2О = 1.92 × 10–2 atm).

Tetragonal perovskite phase Ce0.9Ca0.1AlO2.95 + x was obtained for the first time. Such phase, containing cerium in the oxidation state of 3+, can be promising anode materials for a solid oxide fuel cells (SOFCs). Ce0.9Ca0.1AlO2.95 + _ (space group I4/mcm) was synthesized by the solid-phase method at 1400 & DEG;C in a nitrogen flow with using ammonium oxalate (NH4)2C2O4 to create a reducing atmosphere. Thermogravimetry results showed that Ce0.9Ca0.1AlO2.95 + x was stable to oxidation up to 500 & DEG;C in air and up to 700 & DEG;C in argon (partial pressure of oxygen pO2 =10-4 bar). The thermal expansion coefficient measured by dilatometry was equal to 11.16.10-6 K-1. The temperature dependences of the electrical conductivity (for undoped phase CeAlO3 s = 1.10-3 S/cm and for doped Ce0.9Ca0.1AlO2.95 + x s = 3.10-2 S/cm at 500 & DEG;C in air) were obtained by the electrochemical impedance spectroscopy measurements). The electrical conductivity of these samples at the temperatures range of 350-500 & DEG;C was almost independent of the partial pressure of oxygen pO2 from 10-18 to 0.21 bar, however, there was a slight negative slope at T > 500 & DEG;C (pO2). The total ionic transport numbers measured by the EMF method were close to 1.10-3, which indicated the dominance of electronic conductivity. The measurement of the sign of the thermal-EMF showed that positive charge carriers (holes) were dominant charge carriers.& COPY; 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Composites with the general formulas (1 – x)La2(WO4)3–xSiO2 and (1 – x)Sm2(WO4)3–xSiO2 have been prepared by solid-state reactions. The phase composition and thermodynamic stability of the composites have been demonstrated by X-ray diffraction and thermal analysis (thermogravimetry and differential scanning calorimetry), respectively. The morphology of the composites has been examined by scanning electron microscopy in combination with energy dispersive spectroscopy. The electrical conductivity of the composites has been measured as a function of temperature and oxygen pressure and shown to have an ionic character. Heterogeneous doping of lanthanum and samarium tungstates has been found to have opposite effects: the addition of 1–5 mol % SiO2 nanopowder to La2(WO4)3 leads to an increase in its electrical conductivity by seven times, whereas analogous heterogeneous doping of Sm2(WO4)3 reduces its electrical conductivity.