The mass-transfer of oxygen and hydrogen between the gas phase containing humidified O2 and the La n+1Ni n O3n+1 (n = 1, 2, 3) electrode in contact with the proton-conducting La28-z W4+z O54+1.5z (LWO) electrolyte has been studied. The measurements were performed using the 18O pulse isotope exchange (PIE) technique in the temperature range of 350-800 degrees C under a flow of He + O2 in both dry and humid conditions. Electrochemical studies were carried out using electrochemical impedance spectroscopy (EIS) within the temperature range of 600-800 degrees C in humid air. The PIE study demonstrated that all La n+1Ni n O3n+1 oxides exhibit oxygen surface exchange with O2 and H2O, and the results were further justified by 1H NMR and TGA studies. The mechanism of oxygen surface exchange is discussed. EIS measurements revealed two distinct surface exchange processes for the La3Ni2O7-delta and La4Ni3O10-delta electrodes in contact with LWO, which is explained by the two-step mechanism proposed on the basis of the PIE studies. The EIS and PIE results showed that the hydration of La4Ni3O10-delta occurs through the interaction of oxygen with water on the electrode surface in a humid atmosphere, leading to the formation of hydroxyl groups and their subsequent incorporation into structural oxygen vacancies.

La2-xPrxNi1-yCuyO4+δ (x=0.5, 1, 1.5, y=0.4, 0.6, 0.8) were synthesized by a citrate-nitrate method and studied as cathode materials for IT-SOFCs by Electrochemical Impedance Spectroscopy (EIS) in symmetrical cells based on the Ce0.8Sm0.2O2-δ (SDC) and La28-zW4+zO54+1.5z (z = 0.85, LWO) electrolytes. Phase identification and crystal structure analysis by means of X-ray powder diffraction (XRPD) shows that solubility of copper y decreases with the increase in praseodymium content x due to increasing structural distortions. Thermodynamic stability of La2-xPrxNi1-yCuyO4+δ at intermediate temperatures in air tends to decrease with praseodymium doping level x and increases with copper substitution for nickel y. Oxides with x=0.5 and 0.6≤y≤0.8 are shown to be thermodynamically stable at 700 °C in air. Electrochemical performance of the La2-xPrxNi1-yCuyO4+δ electrodes improves with praseodymium and copper doping. The results of EIS measurements at different temperatures and oxygen partial pressures (P(O2)) reveal that the rate-determining step of the overall electrochemical process is charge transfer, which can be a combination of surface diffusion and bulk diffusion. EIS studies in dry and wet air indicate the presence of proton conduction in the studied electrodes. The area-specific resistances (ASRs) for La2-xPrxNi1-yCuyO4+δ with x=0.5, y=0.6 and y=0.8 in contact with SDC are comparable with those reported for Pr2NiO4+δ and equal to 0.07 and 0.065 Ω cm2 at 800 °C.

La 1.4 Ca 0.6 Ni 0.6 Fe 0.4 O 4+ delta (LCNF), La 1.4 Sr 0.6 Ni 0.6 Fe 0.4 O 4+ delta (LSNF), La 1.4 Ba 0.6 Ni 0.6 Fe 0.4 O 4+ delta (LBNF) have been synthesized by the citrate -nitrate technique. The X -Ray powder diffraction (XRPD) results show an increase in the unit cell parameters and the unit cell volume with the increase in radius of the alkaline earth metal. The oxides possess oxygen excess equal to 0.06 at room temperature and demonstrate semiconductor -type behavior in the 25 - 950 degrees C range. The thermal expansion coefficient (TEC) determined in the 200 - 1000 degrees C interval decreases from 13.9 x 10 -6 (A=Ca) to 13.2 x 10 -6 & Kcy; - 1 (A=Ba) with increasing the dopant size. The electrochemical studies have revealed that the overall polarization resistance of La 1.4 A 0.6 Ni 0.6 Fe 0.4 O 4+ delta is equal to 1.85, 2.61 and 0.4 Omega cm 2 at 800 degrees C for A=Ca, Sr and Ba, respectively. The predominant contribution to the polarization resistance is assigned to the charge transfer - ionic diffusion in the electrodes. It decreases in the row LSNF-LCNFLBNF, which correlates with the increase in ionic conductivity in the oxides.

Surface oxygen exchange in the La2NiO4+a and La1.5Sr0.5Ni1-yFeyO4+a (y = 0.3, 0.4) oxides is analyzed using the data on oxygen permeability through the membranes with different thicknesses measured under various oxygen partial pressure P(O2) gradients in the 800 -1000 & DEG;C range. The increase in P(O2) gradient induced surface limitations in La2NiO4+a leading to a predominant role of surface exchange in the overall oxygen flux. The origin of surface exchange limitations in La2NiO4+a is ascribed to a relatively fast decrease in oxygen excess and Ni3+ concentration with P(O2) reduction compared to La1.5Sr0.5Ni0.7Fe0.3O4+a and La1.5Sr0.5Ni0.6Fe0.4O4+a, which retained an oxygen excess. Faster surface exchange kinetics for La1.5Sr0.5Ni0.6Fe0.4O4+a in comparison with that for La1.5Sr0.5Ni0.7Fe0.3O4+a is interpreted on the basis of surface microstructure obtained by electron backscatter diffraction (EBSD). It is suggested that the observed changes in size, shape and crystallographic orientation of grains in La1.5Sr0.5Ni0.6Fe0.4O4+a (compared to La1.5Sr0.5Ni0.7Fe0.3O4+a) could result in a higher amount of 3d-metal cations in surface layers of the oxide. & COPY; 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Lithium cobalt oxide is a convenient model material for the vast family of cathode materials with a layered structure and still retains some commercial perspectives for microbatteries and some other applications. In this work, we have used ab initio calculations, x-ray diffraction, Raman spectroscopy, and a theoretical physical model, based on quasi-harmonic approximation with anharmonic contributions of the three-phonon and four-phonon processes, to study a temperature-induced change of Raman spectra for LiCoO2. The obtained values of shift and broadening for E-g and A(1g) bands can be used for quantitative characterization of temperature change, for example, due to laser-induced heating during Raman spectra measurements. The theoretical analysis of the experimental results lets us conclude that Raman spectra changes for LiCoO2 can be explained by the combination of thermal expansion of the crystal lattice and phonon damping by anharmonic coupling with comparable contributions of the three-phonon and four-phonon processes. The obtained results can be further used to develop Raman-based quality control tools.

The citric-nitrate technique was used to synthesize polycrystalline Nd2Ni1-xCoxMnO6 & delta; (0.2 & LE; x & LE; 0.5) perovskite oxide. Phase formation was studied by X-ray powder diffraction (XRPD). The unit cell parameters and unit cell volume were refined by the Rietveld analysis, increase with the increasing doping concentration of cobalt. The optical study was performed for the samples in the range of 200-800 nm using UV-vis spectroscopy an absorption peak has been observed in around 330 nm. The energy bandgap (Eg) of the studied samples is slightly influenced by the increasing concentration of cobalt due to the interaction of electronic states between doped Co and other 3d metals. Partial substitution of nickel by cobalt at B-site decreases the Curie temperature (TC) and increased the irreversibility between the zero-field cooled (ZFC) and field-cooled (FC) below TC. The decreasing tendency of TC for the studied samples with the increasing concentration of cobalt in Nd2Ni1-xCoxMnO6 & delta; might be associated with the decreasing Ni/Co-O-Mn bond angle.

La2NiO4+delta, La1.4Ca0.6Ni0.6Fe0.4O4+delta (LCNF0604), La1.4Sr0.6Ni0.6Fe0.4O4+delta (LSNF0604), La1.4Sr0.6Ni0.5Fe0.5O4+delta(LSNF0605) and La1.5Sr0.5Ni0.6Fe0.4O4+delta (LSNF0504) were synthesized by the citrate-nitrate technique with the following four annealing steps at 950 degrees C in air (La2NiO4+delta, LCNF0604, LSNF0604) or in atmosphere with the reduced (10(-5) atm) oxygen partial pressure (LSNF0605, LSNF0504). Phase purity of the samples is confirmed by the X-ray powder diffraction (XRPD). Electrochemical impedance spectroscopy studies of the symmetrical cells based on the proton-conducting La28-zW4+zO54+1.5z (z = 0.85, LWO85) electrolyte reveal that the polarization resistance (R-p) decreases in the row LCNF0604>La2NiO4+delta>LSNF0504>LSNF0604>LSNF0605 in the temperature interval of 600-800 degrees C in wet air. The process at low frequencies related to the surface exchange, provides the most significant contribution to the polarization resistance of the studied cells. Higher polarization resistance for the La2NiO4+delta/LWO85 cell can be associated with blocking of protons/protonic species. The minimal Rp value of 1 Omega cm(2) at 800 degrees C in wet air is demonstrated by the LSNF0605/LWO85 symmetrical cell. The maximal power density for the anode-supported LSNF0605/LWO85/Ni-LWO85 single fuel cell is equal to 55 mW cm(-2) at 750 degrees C. The performance of the fuel cell is limited by the formation of La2O3 at the LWO85/Ni-LWO85 interface due to chemical interaction between NiO and LWO85. To improve the performance of the studied fuel cell the development of new proton-conducting buffer layer stable to LWO85 is required.

The morphotropic phase boundary (MPB) region of the BFO-BTO solid solution is studied by comprehensive macroscopic and local methods, focusing on the synthesis conditions that influence the final phase composition and functional response. The difference between the phase distribution and local switching behavior in two sets of the BFO-BTO solid solutions prepared with different applied pressures is revealed and attributed to the local chemical inhomogeneity forming due to certain differences in the solid-state sintering reactions. More homogeneous mixing of the polar and non-polar phases stimulates the non-polar-to-polar phase transition and widening the MPB region.

La2NiO4+δ, La1.4Ca0.6Ni0.6Fe0.4O4+δ (LCNF0604), La1.4Sr0.6Ni0.6Fe0.4O4+δ (LSNF0604), La1.4Sr0.6Ni0.5Fe0.5O4+δ (LSNF0605) and La1.5Sr0.5Ni0.6Fe0.4O4+δ (LSNF0504) were synthesized by the citrate-nitrate technique with the following four annealing steps at 950 °C in air (La2NiO4+δ, LCNF0604, LSNF0604) or in atmosphere with the reduced (10−5 atm) oxygen partial pressure (LSNF0605, LSNF0504). Phase purity of the samples is confirmed by the X-ray powder diffraction (XRPD). Electrochemical impedance spectroscopy studies of the symmetrical cells based on the proton-conducting La28−zW4+zO54+1.5z (z = 0.85, LWO85) electrolyte reveal that the polarization resistance (Rp) decreases in the row LCNF0604>La2NiO4+δ>LSNF0504>LSNF0604>LSNF0605 in the temperature interval of 600–800 °C in wet air. The process at low frequencies related to the surface exchange, provides the most significant contribution to the polarization resistance of the studied cells. Higher polarization resistance for the La2NiO4+δ/LWO85 cell can be associated with blocking of protons/protonic species. The minimal Rp value of 1 Ω cm2 at 800 °C in wet air is demonstrated by the LSNF0605/LWO85 symmetrical cell. The maximal power density for the anode-supported LSNF0605/LWO85/Ni-LWO85 single fuel cell is equal to 55 mW cm−2 at 750 °C. The performance of the fuel cell is limited by the formation of La2O3 at the LWO85/Ni-LWO85 interface due to chemical interaction between NiO and LWO85. To improve the performance of the studied fuel cell the development of new proton-conducting buffer layer stable to LWO85 is required.

The Ruddlesden-Popper layered nickelates La2NiO4+delta (n = 1, LN21), La3Ni2O7-delta (n = 2, LN32) and La4Ni3O10-delta (n = 3, LN43) were studied as electrodes in symmetrical cells based on Ce0.8Sm0.2O2-delta (SDC) at various temperatures (600 <= T <= 800 degrees C) and oxygen partial pressures (-3 <= log(P(O2)/P0) <= -0.67). Electrochemical Impedance Spectroscopy (EIS) of the selected Lan+1NinO3n+1/SDC cells with similar microstructure reveals that the polarization resistance of the electrodes gradually increases with increasing n, namely by approximate to 0.75 omega cm2 at 800 degrees C in air. The Distribution Function of Relaxation Times (DFRT) analysis of the obtained data shows that the polarization resistance of Lan+1NinO3n+1 includes four distinguishable contributions RHF (1), RHF (2), RMF and RLF. The Ri resistances at fixed temperatures and P(O2) were determined by fitting the obtained impedance spectra using the equivalent circuit consisting of electrolyte resistance and a series of R-CPE elements. Based on the analysis of the Ri = f(T, P(O2)) dependences, the RHF (1), RHF (2) resistances are assigned to the charge transfer through the interfaces and RMF, RLF are interpreted as "chemical" part of the impedance, i.e. ionic transport in the electrode and oxygen dissociation at the electrode surface, respectively. Comparison of the obtained resistances shows that RMF dominates the polarization resistance meaning that ionic transport in the electrodes is the slowest stage of the electrochemical reaction at the studied temperatures in air. The increase in the number of perovskite layers deteriorates ionic diffusion and promotes oxygen dissociation. As RMF > RLF, this leads to an increase in the overall polarization resistance from 0.75 omega cm2 for LN21 to 2.25 omega cm2 for LN43 at 800 degrees C in air.

The single-phase La1.5Sr0.5Ni1-yMnyO4+delta (y = 0, 0.1, 0.2 and 0.3) dense ceramic membranes of different thickness were fabricated by sintering at 1350 degrees C in air. The oxygen permeation flux through the La1.5Sr0.5Ni1-yMnyO4+delta dmembranes slightly decreases at y <= 0.2 and increases by more than one order of magnitude in the 0.2 <= y <= 0.3 range due to a significant increase in the surface oxygen exchange rate. The surface study of La1.5Sr0.5Ni1-yMnyO4+delta by Electron backscatter diffraction technique reveals that manganese doping affects the orientation of crystallites and induces the appearance of planes with higher Miller indices, which are characterized by smaller reticular densities of the 3d-metals. The analysis of the effective paramagnetic moments for La1.5Sr0.5Ni1-yMnyO4+delta shows that manganese doping leads to the formation of mixed Mn3+/Mn4+ oxidation state when y>0.1. As compared to La1.5Sr0.5Ni0.8Mn0.2O4+delta, the significant decrease in surface limitations of the oxygen exchange process at the oxide/gas interface for La1.5Sr0.5Ni0.7Mn0.3O4+delta correlates with the increase in Mn4+ concentration.

The effect of air humidity on the transport properties of the La(2-x)A(x)Ni(1-y)Fe(y)O(4)(+delta) (A=Ca, Sr; x = 0.5, 0.6 and y =0.4, 0.5) oxides was studied in the temperature range of 25-950 degrees C. Total conductivity of the samples decreased with increasing relative humidity (RH), most significantly in the range of 250-550 degrees C. Thermogravimetric analysis in dry and wet air indicated that the observed changes in conductivity could be attributed to the hydration of the samples. The high-temperature X-ray powder diffraction (HT-XRPD) results for La1.4Sr0.6Ni0.5Fe0.5O4,delta (LSNF0605) suggested that the hydration led to the insertion of hydroxide ions into the interstitial sites resulting in the expansion of the rock-salt type layers and shrinkage of the perovskite layers. The Electrochemical Impedance Spectroscopy (EIS) measurements for the LSNF0605/Ce0.8Sm0.2O2-delta (SDC) and LSNF0605/La28-zW4+zO54+1.5z (LWO) symmetrical cells showed that the hydration affected the surface exchange process in LSNF0605. The activation energy of surface exchange decreased with the increase in RH for the LSNF0605/LWO cell indicating that water could participate in the surface exchange. The activation energy of the charge transfer - ionic diffusion process in the LSNF0605 electrode for the LSNF0605/LWO cell possessed smaller values compared to that for the LSNF0605/SDC cell in wet air, suggesting the presence of proton conduction. (C) 2020 Elsevier B.V. All rights reserved.

The La1.5Sr0.5Ni1–yCoyO4+δ (y = 0, 0.1, 0.2, 0.3, 0.4) complex oxides were synthesized by the citrate-nitrate route. The phase purity of the samples was confirmed by the powder X-ray diffraction (PXRD). All studied samples possess the K2NiF4-type structure with space group I4/mmm. The cobalt doping in La1.5Sr0.5Ni1–yCoyO4+δ leads to the expansion of oxygen octahedra in the ab plane and their shrinkage in the c direction, thus, decreasing the structural microstrain. The increase in cobalt concentration results in a gradual increase in oxygen over-stoichiometry, while the oxygen content in La1.5Sr0.5Ni1–yCoyO4+δ shows weak temperature dependence. It is shown that the majority of cobalt cations in these oxides are in the Co3+ state in the whole temperature range studied. The fitting results for the temperature dependencies of the Seebeck coefficient show that the Ni3+ cations are mostly in the low-spin state in La1.5Sr0.5Ni1–yCoyO4+δ in the range of 25–1000°C, although the increase in cobalt content leads to the non-monotonous increase in the fraction of high-spin Ni3+ cations at T > 600°C. The cobalt doping of La1.5Sr0.5Ni1–yCoyO4+δ decreases total conductivity due to the increase in localization of electron holes on the 3d-metal cations.

The La1.5Sr0.5Ni1-yCoyO4+delta (y = 0, 0.2, 0.4) complex oxides were synthesized by the citrate-nitrate method. The disk-shaped dense ceramic membranes with thickness of 0.8 and 1.2 mm for each composition were prepared by uniaxial pressing of the powders and sintering at 1350 degrees C in air. The phase purity of the samples was confirmed by the X-ray diffraction (XRD). The oxygen excess in the samples gradually increased with cobalt substitution and was almost independent of temperature. Oxygen permeation studies through the membranes with different thickness revealed that the cobalt doping eliminated the surface exchange limitations leading to a significant increase in the oxygen surface exchange coefficients (k(ex)). On the contrary, the bulk oxygen diffusion was deteriorated by the cobalt doping, although the oxygen-ion conductivity remained almost unchanged. The electron backscatter diffraction (EBSD) analysis of the surface for the studied ceramic membranes indicated that the observed increase in the k(ex) values could be explained by the effect of cobalt on the crystallographic orientation of crystallites. It is suggested that the cobalt doping increases the surface area of the ((1) over bar 10), ((1) over bar 11) and (011) faces leading to a higher number of 3d-metals in the surface layer of the membranes.

Nd0.5Ba0.5Mn0.5Fe0.5O3-delta (NBMF55) adopts a cubic perovskite structure in the temperature range of 25-1000 degrees C in air. The oxygen deficit in NBMF55, equal to 0.14 at room temperature (RT), noticeably increased with temperature due to oxygen release at T > 330 degrees C. The sample exhibits a moderate value of linear thermal expansion coefficient (LTEC), 14.4 x 10(-6) K-1, within 25-800 degrees C. Total conductivity in NBMF55 increased with temperature yielding 25 S/cm at 1000 degrees C in air. The conduction was thermally activated with the activation energy of 0.33 eV suggesting a hopping mechanism. The impedance measurements for a symmetrical cell based on the Ce0.8Sm0.2O2-delta (SDC) electrolyte material revealed the area-specific resistance (ASR) of 2.2 Omega cm(2) at 700 degrees C in air. (C) 2018 Elsevier B.V. All rights reserved.

The effect of A-site substitution by alkaline earth metals on properties of NdMnO3-delta have been investigated. Nd(x)A(1-x)MnO(3)(A=Ba, Sr, Ca; x=0, 0.25) have been synthesized by a citrate-nitrate combustion technique. The samples were characterized by X-ray powder diffraction (XRPD), thenno-gravimetric analysis and the standard 4 -probe DC technique in the temperature range of 25-1000 degrees C in air. The XRPD patterns revealed that all samples were single-phase and possessed an orthorhombic structure (Puma space group). The Rietveld refinement of the patterns showed that the unit cell volume reduced with a decrease m the dopant size. The temperature dependencies of mass loss indicated that oxygen release from the samples started only at temperatures above 600 degrees C. The total conductivity of the samples indicated a semiconducting behaviour in the whole temperature range studied. The highest value of total conductivity (205 S/cm) was observed for Nd0.75Ba0.25MnO3 at 1000 degrees C in air.

Abstract This work combines new and earlier obtained results on electron hole and oxygen-ion transport in the La2NiO4-based solid solutions. The effect of lanthanum substitution with Ca/Sr and nickel with Fe, Mn, Co or Cu on transport properties of La2− x A x Ni1− y Me y O4+δ was analyzed and discussed at different substitution levels. Besides the changes in concentration and mobility of electron holes induced by the doping with cations of different nature, the partial transformation of Ni3+ from low-spin to high-spin state was shown to have a profound effect on transport properties of these materials leading to a notable decrease in mobility of electron holes, especially in the strontium-rich oxides. The obtained results suggested that the size factor was the main driving force behind the observed transformation of Ni3+. The oxygen-ion transport in La2− x A x Ni1− y Me y O4+δ was characterized by significant surface exchange limitations, which can be reduced only at relatively high concentrations of strontium and iron, and should be taken into account while evaluating the ionic conductivity by means of oxygen permeation or the modified Hebb-Wagner polarization method.

The room-temperature (RT) 57Fe Mössbauer spectra of the La3Ni2−xFexO7±δ oxide solid solutions of Ruddlesden-Popper-type (x = 0.05, 0.10) reveal two doublets for Fe3+ ions in octahedral coordination by oxygen. The existence of two inequivalent sites for Fe at RT is at variance with the space groups Fmmm and Cmcm (Amam) which have been reported for La3Ni2O7±δ. This unexpected finding is discussed in connection with Patterson analyses and Rietveld refinements of powder XRD data for x = 0, 0.05, and 0.10. Alternative structural models have been proposed which can explain the spectroscopic findings and which are compatible with the results from X-ray diffraction.

This study focuses on the application of the La(2)Nia(4)-based cathodes in the electrolyte-supported fuel cells with La0.88Sr0.12Ga0.82Mg0.18O3-delta (LSGM1218) as an electrolyte, Sr2Ni0.75Mg0.25MoO6-delta (SNMM) as an anode and Ce0.8Sm0.2O2-delta (SDC) as an interlayer between the cathode and electrolyte. La2NiO4+delta and La1.5Ca0.5Ni1-yFey-O4+delta (y = 0.3, 0.33, 0.35, 0.37, 0.4) have been synthesized by a citrate-nitrate combustion technique. La1.5Ca0.5Ni0.7Fe0.3O4+delta (LCNF73), La1.5Ca0.5Ni0.67Fe0.33O4+delta (LCNF6733) and La2NiO4+delta have been tested as cathodes for SOFCs. LCNF6733 cathode material has been prepared with different microstructure in fuel cells of similar configuration (designated as I-LCNF6733 and II-LCNF6733). Higher power densities of the II-LCNF6733/SDC/LSGM1218/SNMM fuel cell than those of LCNF73/SDC/LSGM1218/SNMM indicate that iron doping might improve the performance of these oxides as cathode materials. The cells with the II-LCNF6733 and La2NiO4+delta cathodes show similar power densities reaching 277 and 270 mW cm(-2) at 800 degrees C, respectively.