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La 2 NiO 4+δ (LNO) impregnated La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) cathodes were prepared and the effects of the impregnation on the electrical conductivity and oxygen surface exchange property were studied to reveal the enhancement mechanism of oxygen reduction reaction (ORR) catalytic activities. Results of electrochemical impedance spectroscopy (EIS) with distribution of relaxation times (DRT) deconvoluting and electrical conductivity relaxation (ECR) indicate that LNO impregnation into LSCF cathodes enhances the oxygen diffusion process and oxygen surface exchange property. The optimal ORR catalytic activity is achieved after LNO impregnation for two times on the LSCF scaffold (LNO2-LSCF). LNO2-LSCF cathodes also have outstanding performance for their compromise thermal expansion coefficients (TEC) and conductivities. • Proper LNO impregnation enhances the electrochemical performance of LSCF composite cathodes. • LNO impregnation into LSCF cathodes enhances the oxygen surface exchange property. • High performance of LNO impregnated LSCF cathodes is attributed to the advantages of LNO and LSCF. [ABSTRACT FROM AUTHOR]

Abstract: High temperature X-ray diffraction measurements were made on oxygen nonstoichiometric La2 − x Sr x NiO4+ δ in N2–O2 atmosphere at 873–1173K. Crystal structure of La2−x Sr x NiO4+ δ at high temperatures was analyzed using the tetragonal symmetry, I4/mmm. As the amount of excess oxygen increases, the lattice parameter perpendicular to the perovskite and the rock salt layers increases and that parallel to the layers decreases. As a consequence, the cell volume is almost constant regardless of the oxygen content variation. The lattice parameters essentially depend on temperature and δ. The relationship among the lattice parameters, temperature, and δ is expressed by the total differential form of the lattice parameters. The model with linear approximation can well explain the variation of the lattice parameters with δ and temperature. Apparent and true thermal expansion coefficients were calculated from the variation of the lattice parameters with temperature. Crystal structure of La2 − x Sr x NiO4+ δ was estimated by the Rietveld analysis. It is elucidated that the space in the rock salt layer decreases as the acceptor concentration (x +2δ) increases. The variation of the space in the rock salt layer is consistent with the oxygen nonstoichiometric behavior that the interstitial oxygen formation is suppressed as x and δ increase. [Copyright &y& Elsevier]

Abstract: Nonstoichiometric variation of oxygen content in La2 − x Sr x NiO4 + δ (x =0, 0.1, 0.2, 0.3, 0.4) and decomposition P(O2) were determined by means of high temperature gravimetry and coulometric titration. The measurements were carried out in the temperature range between 873 and 1173 K and the P(O2) range between 10−20 and 1 bar. La2 − x Sr x NiO4 + δ showed the oxygen excess and the oxygen deficient compositions depending on P(O2), temperature, and the Sr content. The value of partial molar enthalpy of oxygen approaches zero as δ increases in the oxygen excess region, which indicate that the interstitial oxygen formation reaction is suppressed as δ increase. The relationship between δ and logP(O2) were analyzed by two types of defect equilibrium models. One is a localized electron model, and the other is a delocalized electron model. Both models can well explain the oxygen nonstoichiometry of La2 − x Sr x NiO4 + δ with a regular solution approximation. [Copyright &y& Elsevier]

Abstract: Atomistic computer simulation has been used to predict the most energetically favourable migration pathways for oxygen ion transport in tetragonal La2NiO4. Both interstitial and vacancy mechanisms have been investigated. All of the vacancy mechanisms studied exhibited lower activation energies than the interstitial process. The lowest energy process allowed migration in the a–b plane with an activation energy of 0.35 eV, migration along the c-axis was predicted to have an activation energy of 0.77 eV and interstitial migration in the a–b plane was found to have an energy barrier of 0.86 eV (in agreement with available experimental data). [Copyright &y& Elsevier]

Abstract: The pairing of proton conducting electrolytes with chemically compatible electrode materials is key to their use in electrochemical devices. The reactivity of BaZrO3 with respect to the well known ceramic oxides LaMnO3, LaFeO3, LaCoO3 and La2NiO4 has been investigated with a view to the development of chemically inert cathode materials. Annealing of powder mixtures of the candidate electrode and BaZrO3 showed only formation of small quantities of La2Zr2O7 as a secondary phase. The low level of reaction and good chemical compatibility were further evidenced by diffusion couples of electrode | electrolyte. Only minor inter-diffusion of Ba and La was observed. However, the materials show considerable mismatch in thermal expansivity, resulting in detachment of the electrode from the electrolyte on cooling. These results have predictive relevance across a wider range of systems, and indicate that co-existence can be achieved with careful balancing of chemical activity via chemical substitution. [Copyright &y& Elsevier]

Abstract: The available literature information on the phase equilibria for the La–Ga–Ni–O system has been assessed. Based on the known thermodynamics of boundary oxygen containing systems, La–Ni–O, La–Ga–O, and Ga–Ni–O, and experimental data on phase equilibria in the La2O3–Ga2O3–NiO quasiquaternary system, models have been defined to describe the Gibbs energy of the individual phases. The model parameters have been optimized by least-squares fit to selected experimental information using the CALPHAD-method (Calculation of Phase Diagrams). Chemical potential diagrams of the systems representing fabrications and cathode–anode side operation conditions of LaGaO3-based solid oxide fuel cells (SOFC) were calculated. It has been determined that, neither in fuel cell fabrication conditions nor in operation conditions un-doped LaGaO3 electrolytes and La2NiO4 cathodes are stable in equilibrium with each other but will react to form another phases. [Copyright &y& Elsevier]

This study focuses on the application of the La 2 NiO 4 -based cathodes in the electrolyte-supported fuel cells with La 0.88 Sr 0.12 Ga 0.82 Mg 0.18 O 3-δ (LSGM1218) as an electrolyte, Sr 2 Ni 0.75 Mg 0.25 MoO 6-δ (SNMM) as an anode and Ce 0.8 Sm 0.2 O 2-δ (SDC) as an interlayer between the cathode and electrolyte. La 2 NiO 4+δ and La 1.5 Ca 0.5 Ni 1- y Fe y O 4+δ (y = 0.3, 0.33, 0.35, 0.37, 0.4) have been synthesized by a citrate-nitrate combustion technique. La 1.5 Ca 0.5 Ni 0.7 Fe 0.3 O 4+δ (LCNF73), La 1.5 Ca 0.5 Ni 0.67 Fe 0.33 O 4+δ (LCNF6733) and La 2 NiO 4+δ 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 La 2 NiO 4+δ cathodes show similar power densities reaching 277 and 270 mW cm−2 at 800 °C, respectively. Unlabelled Image • Ca- and Fe-doped La 2 NiO 4 electrodes were tested for the SOFC application. • La 2 NiO 4+δ and La 1.5 Ca 0.5 Ni 0.67 Fe 0.33 O 4+δ cathodes showed best performances. • Iron doping improves efficiency of the La 1.5 Ca 0.5 Ni 1- y Fe y O 4+δ cathodes. • The upper solubility limit of iron in La 1.5 Ca 0.5 Ni 1- y Fe y O 4+δ was shown to be ≈0.33. • The decrease in power density has not exceeded 7% after 130 h of operation at 850 °C. [ABSTRACT FROM AUTHOR]