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This work investigates the enhancement of dielectric properties of La2NiO4-CuO terpolymer nanocomposites using surface modified SiC nanoparticles as fillers. SiC nanoparticles were subjected to acid treatment and annealing at 1000 °C to tailor the surface chemistry. Acid treatment involved immersing the SiC powder in a mixture of H2SO4 and HNO3 acids and sonicating for 30 min, followed by stirring at 60 °C for 6 h. Annealing was carried out at 1000 °C for 2 h in an inert argon atmosphere. La2NiO4 and CuO nanoparticles were synthesized by sol-gel and precipitation techniques respectively, with average particle sizes of 20–40 nm and 10–15 nm confirmed by XRD and FESEM. Nanocomposites were fabricated by dispersing 2–10 wt% of untreated, acid treated and annealed SiC nanoparticles in a La2NiO4-CuO mixture solution, using PVDF as the polymer matrix. Impedance spectroscopy revealed that addition of 5 wt% acid treated SiC resulted in the highest dielectric constant of 42 at 1 kHz, in comparison to 25 for the unfilled polymer. This was attributed to increased interfacial polarization arising from uniform dispersion of nanoparticles and abundant charge trapping sites introduced by the SiC filler.

This work investigates the enhancement of dielectric properties of La 2 NiO 4 -CuO terpolymer nanocomposites using surface modified SiC nanoparticles as fillers. SiC nanoparticles were subjected to acid treatment and annealing at 1000 °C to tailor the surface chemistry. Acid treatment involved immersing the SiC powder in a mixture of H 2 SO 4 and HNO 3 acids and sonicating for 30 min, followed by stirring at 60 °C for 6 h. Annealing was carried out at 1000 °C for 2 h in an inert argon atmosphere. La 2 NiO 4 and CuO nanoparticles were synthesized by sol-gel and precipitation techniques respectively, with average particle sizes of 20–40 nm and 10–15 nm confirmed by XRD and FESEM. Nanocomposites were fabricated by dispersing 2–10 wt% of untreated, acid treated and annealed SiC nanoparticles in a La 2 NiO 4 -CuO mixture solution, using PVDF as the polymer matrix. Impedance spectroscopy revealed that addition of 5 wt% acid treated SiC resulted in the highest dielectric constant of 42 at 1 kHz, in comparison to 25 for the unfilled polymer. This was attributed to increased interfacial polarization arising from uniform dispersion of nanoparticles and abundant charge trapping sites introduced by the SiC filler. [ABSTRACT FROM AUTHOR]

Cathode materials play a crucial role in enabling the widespread adoption of intermediate-temperature solid oxide fuel cells (IT-SOFC) for commercial applications. This study utilized the sol-gel method to prepare a range of perovskite oxides, specifically Sc-doped La 2 Ni 1-x Sc x O 4+δ (x = 0, 0.05, 0.10, and 0.15), without the use of cobalt. The investigation focused on making a study of how the introduction of Sc doping affected the thermal stability, electrochemical properties, and structure of cathode materials. XRD, FE-SEM, and electrochemical workstations were subjected to structural characterization and performance testing of materials. The findings indicate that all the prepared materials have a typical Ruddlesden-Popper structure, and an abundance of additional oxygen can be generated in close proximity to the interstitial by incorporating Sc into the cathode of La 2 Ni 1-x Sc x O 4+δ to increase the oxygen vacancy and improve the catalytic activity of ORR. La 2 Ni 0.9 Sc 0.1 O 4+δ has the highest oxygen surface exchange kinetics, the dissociative adsorption of oxygen is the rate-limiting step at the cathode. At a temperature of 700 °C, the lowest polarization resistance of La 2 Ni 0.9 Sc 0.1 O 4+δ is 0.1298 Ω cm2, while the single cell with La 2 Ni 0.9 Sc 0.1 O 4+δ as the cathode achieves an impressive peak power density of 0.462 W cm−2, thus demonstrating exceptional long-term stability. La 2 Ni 0.9 Sc 0.1 O 4+δ is expected to be a potential high-performance IT-SOFC cathode material. • B‐Site Sc‐doped of cobalt-free La 2 Ni 1-x Sc x O 4+δ cathodes. • Sc-doped creates plentiful oxygen vacancies and increasing oxygen permeability. • Sc-doped improves the ORR activity of La 2 Ni 1-x Sc x O 4+δ cathode. • The TEC of La 2 Ni 0.9 Sc 0.1 O 4+δ cathode is close to conventional electrolyte GDC. • ThePPD of La 2 Ni 0.9 Sc 0.1 O 4+δ cathode at 700 °C is 0.462 W cm−2. [ABSTRACT FROM AUTHOR]

Surface oxygen exchange in the La 2 NiO 4+δ and La 1.5 Sr 0.5 Ni 1- y Fe y O 4+δ (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 (O 2) gradients in the 800–1000 °C range. The increase in P (O 2) gradient induced surface limitations in La 2 NiO 4+δ leading to a predominant role of surface exchange in the overall oxygen flux. The origin of surface exchange limitations in La 2 NiO 4+δ is ascribed to a relatively fast decrease in oxygen excess and Ni3+ concentration with P (O 2) reduction compared to La 1.5 Sr 0.5 Ni 0.7 Fe 0.3 O 4+δ and La 1.5 Sr 0.5 Ni 0.6 Fe 0.4 O 4+δ , which retained an oxygen excess. Faster surface exchange kinetics for La 1.5 Sr 0.5 Ni 0.6 Fe 0.4 O 4+δ in comparison with that for La 1.5 Sr 0.5 Ni 0.7 Fe 0.3 O 4+δ 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 La 1.5 Sr 0.5 Ni 0.6 Fe 0.4 O 4+δ (compared to La 1.5 Sr 0.5 Ni 0.7 Fe 0.3 O 4+δ) could result in a higher amount of 3 d -metal cations in surface layers of the oxide. • Surface exchange limitations in La 2 NiO 4+δ correlate with bulk Ni3+ concentration. • Fe doping in La 1.5 Sr 0.5 Ni 1-y Fe y O 4+δ affects orientation of crystallites. • Increase in number of (001) faces with Fe doping can facilitate surface exchange rate. [ABSTRACT FROM AUTHOR]

The Ruddlesden‒Popper phases pertain to numerous promising materials with the mixed ionic-electronic conductivity used in devices such as oxygen-conducting membranes, solid oxide fuel cells (SOFC), and electrolyzers, which operate in the intermediate temperature region. Their high total conductivity and oxygen mobility make these materials candidates for the mentioned applications. The structure, the oxygen mobility, and the electrochemical characteristics of the promising materials La1.7Ca0.3Ni1 –xCuxO4 + δ (x = 0–0.4) are studied. According to the high-precision XRD data, all synthesized materials are single-phased and have the tetragonal structure. The unit cell parameter c and the cell volume increase upon doping with copper. The content of overstoichiometric interstitial oxygen decreases with doping and the compositions with the high copper content become oxygen deficient. The samples are characterized by the nonuniform oxygen mobility. By and large, the trend for the decrease in the oxygen mobility with the increase in the Cu content is observed in the series of La1.7Ca0.3Ni1 –xCuxO4 + δ samples. By impedance spectroscopy studies, it is shown that the electrodes with the La1.7Ca0.3Ni1 –xCuxO4 + δ functional layers with the copper content x > 0.2 have a higher electrochemical activity. The factors responsible for the efficiency of electrodes are analyzed. The results obtained in this study demonstrate that La1.7Ca0.3Ni0.6Cu0.4O4 + δ materials are the candidates for the air electrodes in electrochemical devices. [ABSTRACT FROM AUTHOR]

Photocatalysis and photoelectrocatalysis, as green and low-cost pollutant treatment technologies, have been widely used to simultaneously degrade pollutants and produce clean energy to solve the problems of environmental pollution and energy crisis. However, the disadvantages of photocatalysts in a narrow absorption range and low utilization rate of solar energy still hinder the practical application. Here we fabricate two-dimensional porous Ruddlensden–Popper type nickel-based perovskite oxide La2NiO4 as a noble metal-free photoanode for photoelectrocatalytic urea oxidation under full spectrum sunlight irradiation. The transient photocurrent density under near infrared (NIR) light (λ > 800 nm) can reach 50 μA cm−2. Urea wastewater was used as the fuel to obtain low-energy hydrogen production, and round-the-clock hydrogen production was achieved with the optimal yield of 22.76 μmol cm−2 h−1. Moreover, a photocatalytic urea fuel cell (PUFC) was constructed with La2NiO4 as the photoanode. The power density under UV-vis-NIR was 0.575 μW cm−2. Surprisingly, the filling factor (FF) under NIR light was 0.477, which was much higher than those under UV-vis-NIR and visible light. The results demonstrated that PUFCs constructed from low-cost nickel-based perovskite oxides have potential applications for low-energy hydrogen production and efficient utilization of sunlight. [ABSTRACT FROM AUTHOR]

A study on the synthesis of black powder (La2NiO4) material using the solution combustion synthesis method at a variation of synthesis temperature of 60, 70, and 80°C was carried out. It produces a mass of black powder of 2 grams by four times of synthesis process. Then, material characterization was performed on the black powder samples obtained by using X-ray Diffraction (XRD) to determine the phases formed, Scanning Electron Microscopy - Energy Dispersive X-ray Spectroscopy (SEM-EDS) to determine the morphology and analyze the composition elemental on the microscale and Fourier Transform Infra-Red (FTIR) to determine chemical bonds. From the whole black powder sample, XRD analysis showed the phases of Dilantanum Nickel Tetraoxide (La2NiO4), Nickel Oxide (NiO), Lanthanum Oxide (La2O3), and Lanthanum Oxide Ht x-form (La2O3 Ht (x-form)). In addition, it was seen from the visible compositions of the phases that the NiO phase looks more dominant and the variation of the synthesis temperature shows that the La2O3 phase was increasing. This was supported by the EDS analysis, which showed that the EDS spectrum contains elements La, Ni, and O where the element O indicates that oxidation occurs in the elements Ni and La. On the other hand, the SEM analysis results confirm that the black powder sample contains the elements La and Ni, based on the high and low electron images contained in the morphology of the black powder sample. In addition, it was also known that the particles in the black powder sample were micron size and had porous morphology. This occurs due to rapid thermal decomposition events and excessive gas development. In addition, FTIR analysis showed that the O-H bond had been reduced and there are still C-O and C-H bonds indicating the presence of organic elements possessed by glycine.

The exploration of non-precious metal catalysts has always been a hot topic. Here, a new type of Ni–La-Nd-Y film was electrodeposited on nickel foam (NF). The Ni–La-Nd-Y film shows outstanding HER activity and stability under alkaline conditions. La 2 NiO 4 makes the electrode surface present a regular layered structure, which greatly increases the number of electrochemically active sites. Ni–La-Nd-Y only needs 46 mV overpotential driving current density of 10 mA cm−2 in 1MKOH solution, which is very close to the HER performance of metal Pt. By doping rare earth elements and taking advantage of the shrinkage characteristics of lanthanides, this work took advantage of the shrinkage characteristics of the lanthanide series and found new ideas for improving catalysts through the combination of different rare earth elements. We fabricated a Ni–La-Nd-Y film, which can accelerate charge transfer and provide more active sites. Among electrocatalysts made with Ni, La, Nd, Y, Ni–La-Nd-Y, for HER, only needs an overpotential of 46 mV to deliver a current density of 10 mA cm−2. This work provides a promising non-noble metal electrocatalyst for water splitting under alkaline conditions. [Display omitted] • One-step electrodeposition Ni–La-Nd-Y technology is convenient and fast. • Ni–La-Nd-Y catalyst η 10 = 42 mV. • La 2 NiO 4 perovskite structure contributes to the improvement of HER performance. [ABSTRACT FROM AUTHOR]

• The oxygen permeation of the La 1.5 Sr 0.5 Ni 1-y Mn y O 4+δ (y =0-0.3) membranes sharply increases at y =0.3. • The activation energy of oxygen permeation flux decreases by two times in the 0.2≤ y ≤0.3 range. • These effects are attributed to the enhanced surface exchange rate in La 1.5 Sr 0.5 Ni 0.7 Mn 0.3 O 4+δ. • The concentration of Mn4+ increases with manganese doping level y in La 1.5 Sr 0.5 Ni 1-y Mn y O 4+δ (y =0.2, 0.3). • Mixed oxidation state Mn+3/Mn+4 is the key factor defining the rate of surface oxygen exchange in La 1.5 Sr 0.5 Ni 1-y Mn y O 4+δ. The single-phase La 1.5 Sr 0.5 Ni 1- y Mn y O 4+δ (y = 0, 0.1, 0.2 and 0.3) dense ceramic membranes of different thickness were fabricated by sintering at 1350 °C in air. The oxygen permeation flux through the La 1.5 Sr 0.5 Ni 1- y Mn y O 4+δ membranes 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 La 1.5 Sr 0.5 Ni 1- y Mn y O 4+δ 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 3 d -metals. The analysis of the effective paramagnetic moments for La 1.5 Sr 0.5 Ni 1- y Mn y O 4+δ shows that manganese doping leads to the formation of mixed Mn3+/Mn4+ oxidation state when y >0.1. As compared to La 1.5 Sr 0.5 Ni 0.8 Mn 0.2 O 4+δ , the significant decrease in surface limitations of the oxygen exchange process at the oxide/gas interface for La 1.5 Sr 0.5 Ni 0.7 Mn 0.3 O 4+δ correlates with the increase in Mn4+ concentration. [ABSTRACT FROM AUTHOR]

In this paper, the effects of infiltration of La2NiO4 (LNO) as a mixed ionic and electronic conductor (MIEC) on the electrochemical performance of porous strontium doped lanthanum manganite (LSM) oxygen electrode of solid oxide cells, in the temperature ranges of 650-850 °C, is reported. XRD and FE-SEM results of the LNO sample calcined at 900 °C confirmed the formation of single phase LNO nanoparticles and uniform distribution of LNO into the porous LSM backbone with a mean particle size of 40 nm, respectively. To characterize the electrochemical behavior of half-cells, electrochemical impedance spectroscopy (EIS) measurement at temperature intervals of 50 °C was carried out. The LNO infiltrated LSM electrodes showed a noticeably decreased activation energy (from 130 to 103 kJ mol-1) and polarization resistance (from 26.2 to 2.5 Ωcm2 at 650 °C) under open circuit voltage (OCV) condition. Besides, the equivalent circuit (EC) modeling revealed that LNO addition has a major effect on the low frequency arc, which is attributed to the surface exchange mechanisms. Decreased amounts of activation energy and polarization resistance of the infiltrated LSM electrode compared to those for the pure one suggest that introduction of LNO nano-particles to the microstructure of LSM is a promising approach to achieve better electrochemical performance even in the low temperature of 650°C.

The La 1.5 Sr 0.5 Ni 1- y Co y O 4+δ (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 °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 ‾ 10) , (1 ‾ 11) and (011) faces leading to a higher number of 3 d -metals in the surface layer of the membranes. [ABSTRACT FROM AUTHOR]

The rising interest shown for adaptable electronics and brain‐inspired neuromorphic hardware increases the need for new device architectures and functional materials to build such devices. The rational design of these memory components also benefits the comprehension and thus the control over the microscopic mechanisms at the origin of memristivity. In oxide‐based valence‐change memories, the control of the oxygen drift and diffusion kinetics is a key aspect in obtaining the gradual analog‐type change in resistance required for artificial synapse applications. However, only a few devices are designed with this in mind, as they are commonly built around ionic insulating active materials. This shortcoming is addressed by using a mixed ionic–electronic conductor as functional memristive material. This work demonstrates how the oxygen content in La2NiO4+δ (L2NO4), tuned through post‐annealing treatments, has a critical influence on the memory characteristics of L2NO4‐based memristive devices. The presence of interstitial oxygen point defects in L2NO4 affects both its structure and electrical properties. High oxygen stoichiometry in the pristine state leads to an increased electrical conductivity, ultimately resulting in an improved memory window with highly multilevel, analog‐type memory programing capabilities, desirable for analog computing and synaptic applications in particular. [ABSTRACT FROM AUTHOR]

The semi conducting properties of La2NiO4 synthesized through sol gel method are studied for the first time using photoelectrochemistry. The X-ray diffraction (XRD) shows that the phase is formed at 900 °C in agreement with the thermal analysis (TG-TDA/DSC). The SEM micrographs exhibit spherical and uniform grains with agglomerated nature, confirmed through laser granulometry. The direct optical gap (1.31 eV) comes from the crystal field splitting of Ni2+ octahedrally coordinated. La2NiO4 is chemically stable in the pH range (5–14) and anodic potentials at pH ~ 12 give rise to surface oxidation of La2NiO4 in the diffusion plateau (0.35–0.6 V). The electrochemical oxygen insertion, studied using chrono-amperometry, is slow with a diffusion coefficient of ~ 2.5 × 10−18 cm2 s−1 at 500 mV. The Mott–Schottky characteristic plotted in alkaline solution (NaOH 0.1 M) indicates p-type conductivity due to oxygen over-stoichiometry well-known in this class of compound. A flat band potential of 0.1 VSCE and hole concentration of 1019 cm−3 were determined from the capacitance measurement. Therefore, the oxide has been successfully tested for the H2 evolution under visible light irradiation. The best activity occurs at pH ~ 13 in presence of S2O32− as reducing agent with H2 liberation rate of 23.6 μmol mn−1 (g catalyst)−1 under visible light flux of 29 mW cm−2. [ABSTRACT FROM AUTHOR]

The development of highly active and stable catalyst materials is the focus of dry reforming of methane (DRM) technology. The effect of substituting transition metals (Mn, Fe, Co, and Cu) on the B-site of La 2 NiO 4 perovskite on the DRM catalytic performance was investigated. Compared to the unsubstituted sample, the Co-substituted sample exhibited reduced reactivity but increased carbon deposition; the Mn-substituted and Fe-substituted samples demonstrated decreased reactivity and carbon deposition; the Cu-substituted sample displayed a slight decrease in CH 4 conversion but a substantial increase in carbon resistance. The effect of the substitution ratios of Cu elements was further investigated. The results showed that Cu substitution could maintain the perovskite phase in the samples. In the 5-h DRM reaction, the reactivity of the samples exhibited a decreasing trend as Cu substitution ratios increased. All Cu-containing samples displayed carbon deposition rates lower than 0.4 mg/(g*h), resulting in an over 90-fold improvement in carbon resistance compared to the La 2 NiO 4 sample. Further investigations revealed that the La 2 Ni 0.6 Cu 0.4 O 4 sample exhibited stable activity during the 50-h DRM reaction with only a small amount of amorphous carbon in the reacted sample (no obvious carbon nanotubes were observed). Characterization results indicated that the enhanced carbon resistance in Cu-substituted samples was attributed to the Ni-Cu alloy formation, which inhibited CH 4 decomposition reactions and reduced solid carbon generation rates. Density functional theory (DFT) calculations showed that the partial substitution of Cu could increase the energy barrier of the CH* dehydrogenation step, which in turn reduced the rate of solid carbon generation. [ABSTRACT FROM AUTHOR]

Lattice defects significantly affect the mechanical properties of crystalline metal oxides. The materials for the components of solid oxide fuel cells (SOFCs) are no exception, and hence understanding of the interplay between lattice defects and the mechanical properties of components is important to ensure the mechanical stability of SOFCs. Herein, we performed an in situ evaluation of the temperature and P(O2) dependence of the elastic moduli of La2NiO4 (LN214), a candidate for the cathode material of SOFCs, using the resonance method to understand the influence of interstitial oxygen on its elastic properties. Above 873 K, both the Young’s and shear moduli of LN214 slightly decreased with increasing P(O2), suggesting that these elastic moduli are correlated with interstitial oxygen concentration and decreased with increasing interstitial oxygen. We analyzed the influence of interstitial oxygen on the Young’s modulus of LN214, based on numerically obtained lattice energy. The P(O2) dependence of the Young’s modulus of LN214 was found to be essentially explained by variation in the c-lattice constant, which was triggered by variation in interstitial oxygen concentration. These findings may contribute to a better understanding of the relationship between lattice defects and mechanical properties, and to the improvement of the mechanical stability of SOFCs.

Double perovskites La 2-x NiO 4-δ doped with Ca and Ba were synthesized via microwave-assisted combustion method and studied as an alternative oxygen carrier (OC) for chemical looping reforming processes (CLR). The OCs, La 2 NiO 4 , La 1. 8 Ca 0. 2 NiO 4 , La 1. 8 Ba 0. 2 NiO 4 and La 1. 8 Ca 0. 1 Ba 0. 1 NiO 4 were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature-programmed reduction and oxidation (TPR/TPO) and cyclic thermogravimetric analysis (TGA). Rietveld's refinement, performed after each redox cycle, confirmed that doping allows smaller amounts of nickel to migrate from the perovskite structure. The double perovskites synthesized for the chemical looping reforming process behave as simple nickel oxide and are considered as alternative oxygen carriers to solve the problems of deactivation due to the interaction of NiO with the support. The Ca-doped OC (La 1.8 Ca 0.2 NiO 4) showed lower NiO concentration outside the structure and smaller crystallite size after the redox cycles, which was associated with a change in the crystal structure, presenting superior performance and stability. The results show that all perovskites have high reactivity in both reduction and oxidation reactions, however the perovskites were not able to uncouple oxygen, which is an unsual behavior for perovskites. Image 1 • The Rietveld refinement contributed to confirm perovskite regeneration capacity. • The La 1.8 Ca 0.2 NiO 4 showed better reactivity and high regeneration capacity. • Nickel-based double perovskites do not present oxygen decoupling property. • Perovskites synthesized exhibit similar behavior to NiO. [ABSTRACT FROM AUTHOR]

The layered perovskite structure material La 2 NiO 4, which is a material with better infrared radiation properties, was synthesized successfully at 950 ºC and above by the molten salt method. The emissivity values of La 2 NiO 4 were all above 0.973 in the 3–5 µm waveband, which was due to the narrow band gap, and those in the 8–14 µm waveband were all above 0.987. The force constants of La 2 NiO 4 were calculated, and it was proven that higher infrared emissivity in the 8–14 µm waveband corresponds to lower force constants. In addition, the high temperature chemical stability of La 2 NiO 4 was studied and it was found that no chemical reactions occurred in La 2 NiO 4 at high temperature. The infrared emissivity of La 2 NiO 4 treated at 1400 ºC was tested. The results showed that the maximum attenuation rate of infrared emissivity was less than 0.40%, indicating that La 2 NiO 4 still had excellent infrared radiation properties after heat treatment. • La 2 NiO 4 was prepared successfully by the molten salt method at 950 ℃. • The emissivity of La 2 NiO 4 was high in the 3–5 µm waveband due to the narrow band gap. • La 2 NiO 4 had a high emissivity of 0.987 in the 8–14 µm waveband. • The force constant was used to analyze infrared radiation in the 8–14 µm waveband. • La 2 NiO 4 has excellent high-temperature chemical stability. [ABSTRACT FROM AUTHOR]

One of the key points in the development of dry reforming of methane (DRM) is the design of catalysts with high activity and stability. The reactivity and carbon deposition properties of La 2 NiO 4 in DRM, as well as its regeneration performance, were studied. The results showed that the in-situ decomposition of La 2 NiO 4 led to a more uniform distribution of smaller Ni0 particles on the La 2 O 3 matrix compared with the directly loaded NiO/La 2 O 3. A temperature-programmed test revealed that the breakthrough curve temperature for La 2 NiO 4 in DRM was 618 °C. The carbon deposition would carry Ni0 metal away from the La 2 O 3 matrix, making the solid carbon unable to be removed promptly due to insufficient oxygen supply, resulting in an increase in the catalyst's instantaneous carbon deposition rate at 650 °C and 750 °C. The regeneration tests showed that the samples' DRM performance and carbon deposition levels remained relatively stable before and after steam regeneration. However, air-regenerated samples exhibited a hysteresis time in DRM due to sintering. Additionally, CO 2 was unable to completely remove carbon deposition from the samples, resulting in a significant increase in carbon deposition when regenerated samples were used for DRM. • La 2 NiO 4 could maintain high reactivity in DRM for its ability of obtaining finely dispersed Ni0 metal on the La 2 O 3 carrier. • There was a breakthrough curve temperature (618 °C) for La 2 NiO 4 in the DRM atmosphere. • The instantaneous carbon deposition rate of La 2 NiO 4 samples increased over time at 650 and 750 °C for DRM. • The steam was the most effective regeneration atmosphere to regenerate La 2 NiO 4 after the DRM reaction, followed by air and finally CO 2. [ABSTRACT FROM AUTHOR]

One of the research priorities in dry reforming of methane (DRM) technology is the development of highly active and stable catalysts. Using crystalline oxides as catalyst precursors is an effective catalyst optimization scheme for DRM. Therefore, the application of La 2 NiO 4 perovskite in DRM was systematically studied, including preparation, characterization, carbon deposition properties, regeneration properties, and B-site doping, etc. This paper is the first part, the effects of preparation methods (sol-gel, co-precipitation, hydro-thermal, and solid-state methods) on the physicochemical properties and DRM performance of La 2 NiO 4 samples were investigated, and the relationship between materials' structure and their catalytic performance was analyzed. The results showed that compared with the samples prepared by the hydro-thermal and co-precipitate methods, the sample prepared by the sol-gel method exhibited the highest conversion of CH 4 and CO 2 (91.4% and 91.5%, respectively) and the best carbon resistance in DRM, which were mainly attributed to its richer microstructure, higher reducibility and basicity. While the lowest DRM performance of the sample prepared by the solid-state method was mainly due to the small amount of reduced amorphous NiO and the weak reducibility of the perovskite phase in this sample, resulting in the inability of perovskite in-situ decomposition under the DRM atmosphere. • A series of La 2 NiO 4 perovskite oxides were synthesized by the sol-gel, co-precipitation, hydro-thermal, and solid-state methods for DRM. • The sample prepared by the sol-gel method (L2N-SG) exhibited the highest reactivity and the best carbon resistance in the DRM. • The best DRM catalytic activity and carbon resistance of L2N-SG were due to its rich microstructure, high reducibility, and high basicity. • The in-situ reduction process of perovskites in the DRM depends on the amount of reduced amorphous NiO and the reducibility of the perovskite phase in the material. [ABSTRACT FROM AUTHOR]

Chromium deposition and poisoning of La2NiO4 cathode of solid oxide fuel cell were studied. La2NiO4 cathode showed stable performance in the presence of metallic interconnects. Comparing with the polarization resistance (Rp) of La2NiO4 cathode in the absence of metallic interconnects, Rp did not change in the presence of metallic interconnect. After electrical conductivity relaxation method, La2NiO4 with high surface oxygen diffusion coefficients working under Cr atmosphere improved the oxygen reduction kinetics and increased cathode O2 reduction reaction rates. No chromium deposition was observed on the La2NiO4 cathode surface after polarization for 20 h at 800°C. The chemical compatibility of La2NiO4/Cr2O3 and La2NiO4/Gd0.1Ce0.9O1.95 (GDC) study indicates that La2NiO4 did not react with Cr2O3 and GDC under the operating temperature. The results indicate that La2NiO4 cathode is a potential chromium-tolerant material of solid oxide fuel cell.

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]

The present work aims at developing a computational model for the prediction of oxygen separation through La2NiO4 disk shaped membranes. The influence of oxygen concentration on the permeation rate was studied experimentally. The mode! has been validated by comparing the numerical results with those of experiments. The optimal diameter of the inner tube for sweep gas and its distance (gap height) from the membrane surface for maximum oxygen permeation has been investigated. For the present geometry, the optimum gap height (P) is in the range of 0.85-1.25 mm and the optimum diameter (D,) is in the range of 1.5-2.5 mm. Finally it is concluded, as indicated by the numerical and experimental investigations, that with increase in the ratio of O2/N2 mixture on the feed side the oxygen permeation rate increases. [ABSTRACT FROM AUTHOR]

• SOFC electrodes were impregnated by the solution method in which oxide nanofilms are formed. • The inclusion of nanofilms of some oxides in SOFC electrodes increases their activity. • The polarizing conductivity of the impregnated electrodes correlates with the ambipolar conductivity of the films. • Submicron barrier layers prevent interaction between the electrode and the YSZ electrolyte. The present paper is a review of our research results (obtained at the Institute of High Temperature Electrochemistry) on the electrode reactions at the Pt|YSZ electrolyte (yttria-stabilized zirconia) interface during the impregnation of porous electrodes by some rare-earth oxides (CeO 2-x , PrO x , TbO x) as well as Tb 1-x Ce x O 2-α mixed oxides. The impregnation was performed in the nitrate solutions of rare-earth elements, in such a way that oxide nanofilms were formed at the surface of the electrolyte. The impact of the submicron barrier Ce 0.8 R 0.2 O 2-a (R = Y, Sm, Tb) films on the polarization resistance of the La 2 NiO 4 |YSZ boundary is studied. A comprehensive review of available literature data is performed. [ABSTRACT FROM AUTHOR]

A solid oxide fuel cell in operando is a complex multiphasic entity under electrical polarization and operating at high temperatures. In this work, we reproduce these conditions while studying transition metal redox chemistry in situ at the cathode. This was achieved by building a furnace that allowed for X-ray absorption near-edge structure and AC impedance spectroscopy data to be obtained simultaneously on symmetrical cells while at operating temperatures. The cell electrodes consisted of phases from the Ruddlesden-Popper family; La2NiO4+δ, La4Ni3O10-δ, and composites thereof. The redox chemistry of nickel in these cathodes was probed in situ through investigation of changes in the position of the X-ray absorption K-edge. An oxidation state reduction (Ni3+ to Ni2+) was observed on heating the cells; this was correlated to changing concentrations of ionic charge carriers in the electrode. Polarizing the cells resulted in dramatic changes to their electrical performance but not to the bulk redox chemistry of the electrode. The implications of this with respect to explaining the polarization behavior are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Single crystal La2NiO4 films were grown on STO (001) substrates by use of pulsed laser deposition (PLD). It was found that these films grow with the c-axis in the out of plane direction up to a certain critical thickness. Films thicker than that resulted in a structural reorientation from c-axis to a-axis out of plane orientation. The evolution of the c and a axis were measured by using a four circle X-ray diffractometer. [Copyright &y& Elsevier]

Abstract: Single-phase La2NiO4 has been prepared using polyvinyl alcohol (PVA) as a complexing agent. Thermogravimetric (TG), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) were used to characterize precursor and derived oxide powders. The particle size and morphologies of La2NiO4 crystallites were characterized by field emission scanning electron microscope (FSEM). The effect of the mol ratios of metal ion to hydroxyl groups in polyvinyl alcohol on the formation of La2NiO4 was investigated. XRD analysis showed that single-phase and well-crystallized La2NiO4 was obtained from precursor with M/OH=1:3 at 900°C. The La2NiO4 ceramics sintered at 1300°C for 4h exhibits an electrical conductivity of 42.5Ω−1 cm−1 at room temperature. [Copyright &y& Elsevier]

Abstract: In order to study the effect of oxygen doping on magnetic correlations in La2NiO4+d, electron spin resonance (ESR) measurements, which allow to characterize the spin fluctuations, have been performed on three compounds with δ = 0.09, 0.12, and 0.17. The ESR parameters anomalies are in relation with charge and spin order in stripes observed by others techniques such as neutron diffraction. [Copyright &y& Elsevier]

Abstract: In this study, the non-stoichiometric redox compounds La2NiO4+δ and La2Ni0.9V0.1O4.15+δ have been tested as an oxidant in selective oxidation of propane in pulse experiments at temperatures between 450 and 650°C. The oxygen contents in the samples at different temperatures were calculated based on back-titration with O2 pulses as well as on TGA. In the case of La2Ni0.9V0.1O4.15+δ over-stoichiometric oxygen was the only active species, responsible for the formation of CO2, C3H6, C2H4 and CH4 while pulsing propane at all investigated temperatures. Contrary, the reactive species in La2NiO4+δ changed from over-stoichiometric oxygen only at 450°C, to both over-stoichiometric and lattice oxygen at 550°C, to lattice oxygen only at 650°C. The activation of lattice oxygen and the consequent formation of Ni metal were detrimental for selectivity to propylene as formation of CO x , CH4 and coke mainly occurred and no olefins were formed. [ABSTRACT FROM AUTHOR]

A composite Ni-La-Ce0.8Gd0.2O2 catalyst was investigated for the autothermal reforming of propane. A stable performance was recorded during a 100 h endurance test with a syngas yield of 85% at 800 °C. The catalyst was also investigated as anode for the direct utilization of propane in solid oxide fuel cells (SOFCs). This catalyst appeared less affected by carbon deposition during SOFC operation than conventional Ni-cermets. Schematic illustration of a SOFC operating with direct utilization of propane [Figure not available: see fulltext.]. [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: A composite Ni–perovskite anode was investigated for operation in dry propane-fed intermediate temperature solid oxide fuel cells (IT-SOFC). A La0.6Sr0.4Fe0.8Co0.2O3 (LSFCO) perovskite, characterized by mixed electronic–ionic conductivity, was used to support a highly dispersed Ni-phase. However, the catalyst structure was modified during SOFC operation. X-ray diffraction analysis of the electrocatalyst showed that, after operation, Ni was mainly present as La2NiO4; whereas, the LSFCO structure was partially modified into a lanthanum-depleted SrFe1−x Co x O3−y (SFCO) perovskite structure. These results were corroborated by X-ray photoelectron spectroscopy (XPS). Transmission electron microscopy (TEM) analysis showed the presence of a suitable dispersion of a nanosized Ni-phase and a strong interaction of Ni-enriched particles with the perovskite substrate. High reaction rates for the propane reaction were achieved with this electrocatalyst while minimizing carbon deposition. Power densities of about 300mWcm−2 for dry propane oxidation were obtained at 800°C in the presence of a thick gadolinia-doped ceria electrolyte. Fuel cell time-tests indicated promising electrochemical stability. [Copyright &y& Elsevier]

Abstract: In order to elucidate the relation between thermodynamic quantities, the defect structure, and the defect equilibrium in La2− x Sr x NiO4+ δ , statistical thermodynamic calculation is carried out and calculated results are compared to those obtained from experimental data. Partial molar enthalpy of oxygen and partial molar entropy of oxygen are obtained from δ-P(O2)–T relation by using Gibbs–Helmholtz equation. Statistical thermodynamic model is derived from defect equilibrium models proposed before by authors, localized electron model and delocalized electron model which could well explain the variation of oxygen content of La2− x Sr x NiO4+ δ . Although assumed defect species and their equilibrium are different, the results of thermodynamic calculation by localized electron model and delocalized electron model show minor difference. Calculated results by the both models agree with the thermodynamic quantities obtained from oxygen nonstoichiometry of La2− x Sr x NiO4+ δ . [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: La2NiO4 coatings were co-sputtered on rotating substrates from metallic La and Ni targets in the presence of a reactive argon–oxygen gas mixture. This material is a potential candidate as cathode material for Intermediate Temperature-Solid Oxide Fuel Cells. The structural and chemical features of these films have been determined by X-ray Diffraction and Scanning Electron Microscopy. Their electrical properties have been characterised using the four point probe method and by Complex Impedance Spectroscopy measurements. It is shown that the as-deposited coatings, initially amorphous, crystallise in the LaNiO3 perovskite-type oxide or in the convenient K2NiF4 structure as a function of their composition. The electrical measurements show a clear relation between resistivity and structure of the coatings. Despite electrical resistivity values close to the theoretical ones, the activation energy of a coating presenting the convenient K2NiF4 structure is slightly higher than those given in the literature data. [Copyright &y& Elsevier]

Abstract: X- and Q-band ESR experiments on ceramics and single crystals of La2NiO4+δ (0.03≤ δ ≤0.17) are reported. The observed intrinsic ESR signals were interpreted in terms of ferromagnetic resonance of isolated oxidized nickel species in the lattice. The origin of the ferromagnetic component differs according to the δ value, consistent with the phase diagram and the phenomenon of charge and spin order. The ESR spectra on powders exhibit an anisotropic signal attributed to the presence of a magnetic local field, induced by the external magnetic field applied during the first ESR measurement. For specific value of δ, the ESR spectra show a “multilines signal” from the origin which could be due to the presence of magnetic polarons which are pinned on the surface. An ESR study vs. temperature for a powder sample with δ =0.16 shows that the linewidth evolution is in relation with the transition from a dynamic stripe to a static stripe state at 160K. At high temperature (T >600K), a polaronic liquid is observed. [Copyright &y& Elsevier]

High temperature measurements on Ln2NiO4 + δ (Ln=La, Pr, Nd) have been performed indicating a complex behavior in PAC experiments which can be attributed to fluctuating electric field gradients caused by the high mobility of excess oxygen. [ABSTRACT FROM AUTHOR]

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]

Abstract: LaNiO3 and La2NiO4 type perovskites were prepared by the “self-combustion” method and were used as catalyst precursors for the CO2 reforming of CH4 reaction at 700°C. The catalysts were tested in reduced and non-reduced form. High CH4 and CO2 conversion were obtained without carbon deposition. This result was explained by the occurrence of the RWGS (reverse water gas shift) reaction. The La2NiO4 perovskite used as precursor presents the smallest nickel particles after the reduction treatment. Consequently the catalytic activity is higher than that obtained with Ni/La2O3 or LaNiO3. When La2NiO4 is used without treatment prior to the reaction high methane and carbon dioxide conversions are reached but a carbon deposition is observed. The perovskite structure is not completely transformed and the presence of metallic nickel particles at the surface of La2NiO4 would be responsible for the carbon deposition. It is assumed that the role of the support is to allow the activation of carbon dioxide, which is favoured over La2O3 whereas it is limited over La2NiO4. Consequently the reaction between the complex C–Ni species (resulting from methane activation at the surface of the nickel particle) and gaseous CO2 is inhibited over Ni/La2NiO4 leading to a carbon accumulation at the surface of the catalyst. As soon as the perovskite structure is completely transformed, after reductive treatment or during the reaction, a high activity is reached and no carbon deposition was further observed, the catalytic performances being optimal when the average nickel particles size is the smallest. [Copyright &y& Elsevier]

La2NiO4 tubular membranes of relative density over 92% were used to separate oxygen from air and facilitate the partial oxidation of methane to H2 and CO at 900 °C. When methane was fed into a tube of inner surface area 5.11 cm2 at a rate of 10.5 ml/min, methane throughput conversion was 89%, CO selectivity 96%, H2/CO ratio 1.5, and the equivalent oxygen flux was 6.8 ml/min. The surface of the La2NiO4 membrane exposed to CH4 decomposed into La2O3 and Ni, while the surface in contact with air remained almost unchanged. It is suggested that the conversion of methane in the membrane reactor involves the reforming of methane by the H2O and CO2 catalyzed by nickel. [Copyright &y& Elsevier]

A large amount of more graphitic carbon nanotubes with a narrow size distribution was produced from catalytic decomposition of CH4 over pre-reduced LaNiO3, La4Ni3O10, La3Ni2O7 and La2NiO4. The structure and component of fresh and reduced LaNiO3, La4Ni3O10, La3Ni2O7 and La2NiO4 were determined by X-ray diffraction (XRD). The carbon nanotubes obtained were characterized by means of transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Thermal oxidation of carbon nanotubes in air was made by thermogravimetric experiments (TG). The results revealed that the value of La/Ni in different catalyst precursors influences the diameter distribution and graphitic degree of carbon nanotubes. Lower La/Ni leads to wider diameter and higher graphitic degree of carbon nanotubes. [ABSTRACT FROM AUTHOR]

Lattice defects significantly affect the mechanical properties of crystalline metal oxides. The materials for the components of solid oxide fuel cells (SOFCs) are no exception, and hence understanding of the interplay between lattice defects and the mechanical properties of components is important to ensure the mechanical stability of SOFCs. Herein, we performed an in situ evaluation of the temperature and P(O2) dependence of the elastic moduli of La2NiO4 (LN214), a candidate for the cathode material of SOFCs, using the resonance method to understand the influence of interstitial oxygen on its elastic properties. Above 873 K, both the Young's and shear moduli of LN214 slightly decreased with increasing P(O2), suggesting that these elastic moduli are correlated with interstitial oxygen concentration and decreased with increasing interstitial oxygen. We analyzed the influence of interstitial oxygen on the Young's modulus of LN214, based on numerically obtained lattice energy. The P(O2) dependence of the Young's modulus of LN214 was found to be essentially explained by variation in the c-lattice constant, which was triggered by variation in interstitial oxygen concentration. These findings may contribute to a better understanding of the relationship between lattice defects and mechanical properties, and to the improvement of the mechanical stability of SOFCs. [ABSTRACT FROM AUTHOR]