Oxygen-deficient Perovskite Research Articles

Direct observation of infinite NiO2 planes in LaNiO2 films

Epitaxial thin films of LaNiO2, which is an oxygen-deficient perovskite with “infinite layers” of Ni1+O2, were prepared by a low-temperature reduction of LaNiO3 single-crystal films on NdGaO3 substrates. We report the high-angle annular dark-field and bright-field scanning transmission electron microscopy observations of infinite NiO2 planes of c-axis-oriented LaNiO2 epitaxial thin films with a layer stacking sequence of NiO2/La/NiO2. Resistivity measurements on the films show T2 dependence between 400 and 150 K and a negative Hall coefficient.

(Invited) Bifunctional Oxide Nanocomposite Catalysts for Reversible Electrochemical Energy Technologies

It is well known that energy conversion and storage through electrochemical reactions are the most important energy technologies available today. They include low-temperature polymer electrolyte fuel cells, metal-air batteries, and water electrolyzers, which have many advantages over traditional gasoline combustion such as better overall efficiency, high energy density, and the reduction in CO2 and other emissions [1-3]. These electrochemical energy technologies greatly rely on the oxygen reduction reaction (ORR) and evolution reaction (OER), which is one pair of the most important electrochemical reactions. In particular, one of important applications of bifunctional ORR/OER oxygen catalysts, which is simultaneously active for the ORR and the OER, is for utilized reversible fuel cells. They can significantly reduce the capital cost and enhance energy density. For example, a single device, during the day time, solar generated electricity can be stored via water splitting into H2 and O2 through an electrolyzer [4]. During the night time, the stored H2 and O2 can be used back in a fuel cell to supply electricity. Thus, a single device is able to be operated in both electrolyzer and fuel cell models. However, the energy conversion efficiency is greatly dependent on the performance of the bifunctional catalysts towards the oxygen evolution for water splitting and oxygen reduction in a fuel cell. The other need of bifunctional catalysts is for rechargeable metal-air batteries such as zinc-air and lithium-air cells. They can provide much higher energy density compared to conventional lithium ion battery [5,6]. This is due to their opening air electrodes, which no longer need to store active species within batteries. Instead of, they can continuously intake O2 from air. Oxygen reduction and oxygen evolution are associated with the battery discharging and charging processes, respectively. Current challenges for developing these highly demanded reversible electrochemical energy conversion and storage is the lack of effective cathode catalysts to simultaneously catalyzing both reactrions [7]. High reaction overpotentials, which mean sluggish kinetics, require catalysts containing large amounts of precious metals such as Pt and Ir to enhance reaction activity and durability. Unfortunately, high cost and limited supply of these precious metals have become a grand challenge for widespread applications of these clean energy technologies [8,9]. Even worse, the highly ORR active Pt is not a good catalyst for the OER. Likewise, the OER active Ir is not an optimal catalyst for the ORR. Thus, development of highly efficient ORR/OER bifunctional catalysts is desperately demanded for such clean energy technologies. In this presentation, based on our ongoing researches [4,10-15], I will discuss several bifunctional oxide nanocomposite catalysts. They includes (1) oxygen-deficient perovskite oxides, (2) transition metal oxides, (3) highly stable and active nanocarbons, and (4) their integrated nanocomposites. In addition, perspectives on these catalysts, future approaches, and possible pathways to address current challenges are discussed as well. Reference [1] G. Wu, P. Zelenay, Acc. Chem. Res., 46 (2013) 1878-1889. [2] Q. Li, R. Cao, J. Cho, G. Wu, Adv. Energy Mater., 4 (2014) 1301415. [3] Q. Li, R. Cao, J. Cho, G. Wu, Phys. Chem. Chem. Phys., 16 (2014) 13568-13582. [4] S. Gupta, W. Kellogg, H. Xu, X. Liu, J. Cho, G. Wu, Chem. An Asian J., (2015) DOI: 10.1002/asia.201500640. [5] J.S. Lee, S. Tai Kim, R. Cao, N.S. Choi, M. Liu, K.T. Lee, J. Cho, Advanced Energy Materials, 1 (2011) 34-50. [6] G. Wu, N.H. Mack, W. Gao, S. Ma, R. Zhong, J. Han, J.K. Baldwin, P. Zelenay, ACS Nano, 6 (2012) 9764–9776. [7] S. Gu, B. Xu, Y. Yan, Annual review of chemical and biomolecular engineering, 5 (2014) 429-454. [8] G. Wu, K.L. More, C.M. Johnston, P. Zelenay, Science, 332 (2011) 443-447. [9] F. Jaouen, E. Proietti, M. Lefèvre, R. Chenitz, J.-P. Dodelet, G. Wu, H.T. Chung, C.M. Johnston, P. Zelenay, Energy Environ. Sci., 4 (2011) 114-130. [10] X. Liu, W. Liu, M. Ko, S. Chae, S. Park, A. Casimir, G. Wu, J. Cho, Adv. Func. Mater., 25 (2015) 5799–5808. [11] X. Liu, M. Park, M.G. Kim, S. Gupta, G. Wu, J. Cho, Angew. Chem.-Int. Edit., 54 (2015) 9654–9658. [12] C.-F. Chen, G. King, R.M. Dickerson, P.A. Papin, S. Gupta, W.R. Kellogg, G. Wu, Nano Energy, 13 (2015) 423–432. [13] X. Liu, M. Park, M.G. Kim, S. Gupta, X.J. Wang, G. Wu, J. Cho, Nano Energy, (2015) doi:10.1016/j.nanoen.2015.1011.1030. [14] X.L. Wang, Q. Li, H. Pan, Y. Lin, Y. Ke, H. Sheng, M.T. Swihart, G. Wu, Nanoscale, 7 (2015) 20290-20298. [15] Q. Li, H. Pan, D. Higgins, R. Cao, G. Zhang, H. Lv, K. Wu, J. Cho, G. Wu, Small, 11 (2015) 1443–1452.

Bifunctional Catalyst of Core–Shell Nanoparticles Socketed on Oxygen-Deficient Layered Perovskite for Soot Combustion: In Situ Observation of Synergistic Dual Active Sites

In this letter, two functional reaction sites, i.e., massive Co core–shell nanoparticles and oxygen-deficient layered perovskite, have been combined into a bifunctional catalyst, which exhibits very high activity in soot combustion. Environmental transmission electron microscopy (TEM), in situ Raman spectroscopy, and other characterizations were applied simultaneously to study the soot consumption process online.

Synthesis and preliminary study of La4BaCu5O13 + δ and La6.4Sr1.6Cu8O20 ± δ ordered perovskites as SOFC/PCFC electrode materials

La4BaCu5O13+δ (LBCu) and La6.4Sr1.6Cu8O20±δ (LSCu) oxygen deficient perovskites, synthesized by a Pechini-type gel combustion method, have been investigated as potential cathode materials for IT-SOFC applications. The thermal stability and chemical compatibility with SOFC/PCFC electrolyte materials are examined using X-ray diffraction technique. For both compounds, no structural change is detected in air until 900°C. The evolution of cell parameters with temperature shows thermal expansion coefficients (TEC) of 17.3×10−6K−1 and 12.1×10−6K−1 for LBCu and LSCu, respectively. For LBCu, the formation of oxygen vacancies is evidenced between 700 and 900°C in air. Chemical reactivity tests with several SOFC electrolyte materials reveal a high reactivity of both cuprates with YSZ, GDC and, to a lesser extent, with LSGM. On the other hand, and contrary to what occurs for LSCu, LBCu presents an excellent chemical compatibility with doped barium cerate and zirconate, opening further perspectives for this material as possible SOFC or PCFC cathode. LBCu material presents a quite high electrical conductivity with metallic-type behavior.

Magnetic Ordering in Sr3YCo4O10+x.

Transition-metal oxides often exhibit complex magnetic behavior due to the strong interplay between atomic-structure, electronic and magnetic degrees of freedom. Cobaltates, especially, exhibit complex behavior because of cobalt’s ability to adopt various valence and spin state configurations. The case of the oxygen-deficient perovskite Sr3YCo4O10+x (SYCO) has attracted considerable attention because of persisting uncertainties about its structure and the origin of the observed room temperature ferromagnetism. Here we report a combined investigation of SYCO using aberration-corrected scanning transmission electron microscopy and density functional theory calculations. Guided by theoretical results on Co-O distances projected on different planes, the atomic-scale images of several different orientations, especially of the fully oxygenated planes, allow the unambiguous extraction of the underlying structure. The calculated magnetic properties of the new structure are in excellent agreement with the experimental data.

Oxide ion conductivity in doped NdBaInO4

Oxide ion conductivity in doped NdBaInO4 with new type oxygen deficient perovskite was studied and it was found that doping Ti to In site is effective for increasing the oxide ion conductivity. Since increasing amount of doped Ti increased the partial electronic conductivity under reducing atmosphere, the optimized amount of Ti doped for In site exists around 20mol%, namely, NdBaIn0.8Ti0.2O4. The estimated transport number of oxide ion in this optimized composition was higher than 0.8 from H2–O2 oxygen concentration cell, however, it is lower than 0.1 from N2–O2 cell because the hole conduction is dominant in high PO2 range. Consequently, although the oxide ion conductivity is around log(σ/Scm−1)=−2.5 at 1173K, this study reveals that Ti doped NdBaInO4 which is unique edge oxygen facing structure, is a new family of oxide ion conductor.

Efficient Bi-Functional Electrocatalysts of Strontium Iron Oxy-Halides for Oxygen Evolution and Reduction Reactions in Alkaline Media

Strontium iron oxyhalide perovskitic oxides were investigated by electrochemical characterization as bi-functional electrocatalysts for oxygen evolution (OE) and oxygen reduction (OR) reactions in alkaline media. The electrochemical investigations showed that the presence of lower levels of oxygen and higher levels of chloride, as in Sr4Fe3O8Cl2 and Sr2FeO2Cl2 significantly enhanced the oxygen evolution and reduction over the other perovskitic oxides. Additionally, Sr4Fe3O8Cl2 and Sr2FeO2Cl2 was proven to have high bi-functional activity due to an overpotential gap (ΔE = 0.70 V) between the OER and ORR much lower than that of other similar perovskite bi-functional catalysts. In comparison with other strontium iron oxyhalide based electrocatalysts, Sr2FeO2Cl2 was shown to have higher OER activities among all investigated catalysts. This work demonstrates that the oxygen-deficient layered perovskites of the type A2BO2X2 are a new class of high-performance electrocatalysts for oxygen evolution (OE) and oxygen reduction (OR) reactions in alkaline media.

Density functional study on redox energetics of LaMO3−δ (M=Sc–Cu) perovskite-type oxides

This study evaluates the redox energetics of LaMO3−δ (M=Sc–Cu) perovskite-type oxides via generalized gradient approximation (GGA) to DFT. Two different approaches to redox energetics of oxygen deficient perovskites of strongly non-stoichiometric (δ=0.5) and dilute defect limits (δ→0) are studied. In the first approach the enthalpies of oxidation are calculated using the stoichiometric end-compounds of LaMO3 and LaMO2.5. The most common structures for the reduced lanthanides and strontides similar to the ones experimentally reported for SrMnO2.5, SrFeO2.5, and LaNiO2.5 are considered. The second approach to the oxidation enthalpies termed (δ→0) follow the trend observed experimentally. This approach represents the experimental conditions of the measured oxygen enthalpies, and is hampered less by the artificial features due to spurious self-interaction errors in GGA.

Synthesis and thermoelectric properties of La0.8Sr0.2CuO2.4+δ

Oxygen deficient perovskites are potential candidate materials for thermoelectric power generation and applications in solid oxide fuel cells. In this study, single phase La0.8Sr0.2CuO2.4+δ compound was synthesized by a citrate method. The room temperature DC electrical conductivity was 1774S/cm which decreased to 650S/cm with an increase in temperature, suggesting the on-set of semi-metallic behavior. The Seebeck measurements indicated p-type conduction in La0.8Sr0.2CuO2.4+δ which was low at room temperature and increased with increasing temperature. The maximum ZT value (7.24×10−3) was obtained at 700°C.

Structural and magnetic properties of the new brownmillerite oxides La1−xNaxSrMn2O5+δ (0.1 ≤ x ≤ 0.3)

Na-doped brownmillerite oxides La1−xNaxSrMn2O5 (x = 0, 0.1, 0.2 and 0.3) were synthesized by the solid state reaction method at high temperature. The structural and magnetic properties of the samples were investigated by X-ray diffraction and magnetization experiments. The results from X-ray diffraction analysis showed that all samples were single phase and crystallized in the orthorhombic system, with space group Pnma. This structure can be described as an oxygen-deficient perovskite, resulting in a sequence of regular alternating layers of corner-sharing BO6 octahedra (O) and BO4 tetraedra (T) according to axis b. The results from magnetization versus temperature measurements in a magnetic applied field of 0.05 T indicated that the samples underwent a paramagnetic–ferromagnetic transition with decreasing temperature. The Curie temperature TC decreased from 365 to 345 K with Na content. An electronic phase separation model considering the formation of ferromagnetic clusters in the antiferromagnetic matrix was proposed to interpret the observed magnetization results for the Na-substituted samples. Overall, the present study provided an effective approach to achieve new functional materials based on naturally occurring layered systems such as La1−xNaxSrMn2O5+δ, for possible application in the spintronics industry.

Oxygen non-stoichiometry and mixed conductivity of La0.5Sr0.5Fe1–x Mn x O3–δ

Oxygen non-stoichiometry, thermal expansion, and high-temperature transport properties of perovskite-type La0.5Sr0.5Fe1– x Mn x O3–δ , where x = 0, 0.10, 0.17, 0.25, and 0.33 have been studied in the oxygen partial pressure range 10−19 to 0.5 atm. The major trends observed under oxidizing and reducing conditions were found to exhibit substantial differences due to changes in the manganese oxidation state. The high $$ {p}_{{\mathrm{O}}_2} $$ range is characterized with replacement of Fe4+ by Mn4+ cations, which results in the decreasing concentration of mobile p-type electronic carriers, oxygen non-stoichiometry, and thermal expansion. The oxygen pressure decrease below 10−5 atm is accompanied with gradual reduction of manganese to Mn3+/Mn4+ mixed oxidation state, followed by larger variations in the non-stoichiometry, electrical conductivity, and thermal expansion. The observed increase in the oxygen ion conductivity with manganese content can be explained as a consequence of strong Mn preference for fivefold oxygen coordination in the oxygen-deficient perovskite lattice, which promotes the formation of oxygen vacancies available for anion diffusion. The calculated oxygen permeation fluxes through La0.5Sr0.5Fe0.67Mn0.33O3–δ membranes at 950 °C become higher compared with La0.5Sr0.5FeO3–δ , which may be advantageous for application in the integrated processes of oxygen separation, partial hydrocarbon oxidation, and hydrogen production.

ChemInform Abstract: Charge Ordering in Cobalt Oxides: Impact on Structure, Magnetic and Transport Properties

AbstractReview: 92 refs.

Modeling Water Reduction on Doped Ceria Thin Films

In recent years, there has been an increasing interest in understanding electrochemical reactions on oxide surfaces. The advent of techniques such as ambient-pressure x-ray photoelectron spectroscopy (AP-XPS) has helped to provide a better understanding of aspects such as the nature of the surface1-2 and the species involved in the reactions3-4. However, a quantitative connection between macroscopic rates and the surface structure and dynamics remains elusive. Among these reactions, water electrolysis has attracted interest due to favorable kinetics when compared to low temperature electrolysis5. Doped ceria, a mixed ionic and electronic conductor, is a potential candidate for this reaction due to higher stability and more efficient use of the electrode area compared to currently available materials, such as nickel/yttria-stabilized zirconia cermet6. Recent spectroscopic studies of water reduction/oxidation on doped ceria have shed valuable new insights about this reaction, but uncertainties remain in the interpretation of these measurements (in terms of a rate-determining step) and the connection to macroscopic rates3,4. In order to better connect spectroscopic observations to macroscopic rates, we have developed a thermodynamically self-consistent elementary kinetic model for H2/H2O exchange on the surface of ceria. This model considers both the bulk defect thermodynamics, as well as the effects of cation reconstruction/segregation at the surface and space charge effects, both of which are expected to alter the defect chemistry and concentrations of reactive intermediates. We have used this model to explore a variety of mechanisms and rate-limiting steps proposed in the literature3,4, and to predict the expected nonlinear electrochemical rate law. This includes prediction of the nonlinear electrochemical impedance (NLEIS) response of thin film ceria electrodes, in an approach similar to our previous studies of O2 reduction kinetics on perovskite thin films8. References Mueller, D. N.; Machala, M. L.; Bluhm, H; Chueh, W. C. Redox activity of surface oxygen anions in oxygen-deficient perovskite oxides during electrochemical reactions. Nature Comm. 2015, 6, 6097Chueh, W.C.; McDaniel, A. H.; Grass, M. E.; Hao, Y; Jabeen, N; Liu, Z; Haile, S. M.; McCarthy, K. F.; Bluhm, H; El Gabaly, F. Highly Enhanced Concentration and Stability of Reactive Ce3+ on Doped CeO2 Surface Revealed in Operando. Chem. Mater. 2012, 24, 1876-1882Zhang, C; Yu, Y; Grass, M. E; Dejoie, C; Ding, W; Gaskell, K; Jabeen, N; Hong, Y. P; Shavorskiy, A; Bluhm, H; Li, W. X; Jackson, G. S; Hussain, Z; Liu, Z; Eichhom, B. W. Mechanistic Studies of Water Electrolysis and Hydrogen Electro-Oxidation on High Temperature Ceria-Based Solid Oxide Electrochemical Cells. J. Am. Chem. Soc. 2013 , 135, 11572-15579Feng, Z. A; El Gabaly, F; Ye, X; Shen, Z. X; Chueh, W. C. Fast vacancy-mediated oxygen ion incorporation across the ceria-gas electrochemical interface. Nature Comm. 2014 , 5, 4374Brisse, A; Chefold, J; Zahid, M. High Temperature Water Electrolysis in Solid Oxide Cells. International Journal of Hydrogen Energy. 2008, 33, 5375-5382Nakamura, T; Yashiro, K; Kaimai, A; Otake, T; Sato, K; Kawada, T; Mizusaki, J. Determination of the Reaction Zone in Gadolinia-Doped Ceria Anode for Solid Oxide Fuel Cell. J Electrochem Soc. 2008, 155, B1244-B1250Wilson, J. R; Schwartz, D. T; Adler, S. B. Nonlinear electrochemical impedance spectroscopy for solid oxide fuel cell cathode materials. Electrochimica Acta. 2006, 51, 1389-1402Wilson, J.R.; Sase, M; Kawada, T; Adler, S. B. Measurement of Oxygen Exchange Kinetics on Thin-Film La0.6Sr0.4CoO3-δ Using Nonlinear Electrochemical Impedance Spectroscopy. Electrochemical and Solid State Letters. 2007, 10, B81-B86

ChemInform Abstract: Double Cationic‐Anionic Ordering in Ba‐Based Oxygen‐Deficient Perovskites

AbstractReview: 64 refs.

Double Cationic‐Anionic Ordering in Ba‐Based Oxygen‐­Deficient Perovskites

AbstractComplex cationic‐anionic ordering in barium‐based oxygen deficient perovskites is reviewed. Considering the parent ABO3 structure, the ordering between barium and a rare earth cation in the A site generates three classes of oxides, called double, triple and nanoscale ordered quintuple perovskites. From the ordering between a transition element (Fe, Co) and a larger cation on the B site two structural families are obtained, containing calcium and yttrium respectively. These oxides offer a vast playground for the investigation of magnetic and transport properties.

Charge Ordering in Cobalt Oxides: Impact on Structure, Magnetic and Transport Properties

AbstractThis review shows the great impact of charge ordering upon the magnetic and transport properties of mixed valent Co4+/Co3+ and Co3+/Co2+ cobalt oxides. The relationships between charge ordering and physical properties are described for three structural families: the ordered oxygen deficient perovskites and the Ruddlesden and Popper (RP) derivative La1.5Sr0.5CoO4, the layered NaxCoO2 series and the “114” CaBaCo4O7 oxide.

Oxygen-deficient BaTiO3−x perovskite as an efficient bifunctional oxygen electrocatalyst

Perovskite oxide catalysts have emerged as the most promising bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts for electrochemical energy conversion and storage. In this work, a new type of oxygen-deficient BaTiO3−x has been synthesized using a sol–gel method followed by a reductive heat treatment at 1300°C in vacuum. The prepared perovskite nanoparticles have an average particle size on the order of 100nm with uniform size distribution. X-ray diffraction shows that this perovskite catalyst consists of a significant amount of hexagonal BaTiO3−x. State-of-the-art IrO2 nanoparticles were also prepared in this work, which were used for reference and has excellent OER activity. Importantly, the oxygen-deficient perovskite catalysts exhibited high catalytic activity simultaneously for the ORR and the OER in alkaline electrolyte. The more challenged OER activity measured with the perovskite exceeds the IrO2 catalyst at relatively low potentials (<1.6V) evidenced by a much reduced onset potential (1.32V) and increased current density. In order to clearly elucidate the structure of the oxygen-deficient BaTiO3−x catalysts, X-ray and neutron diffraction experiments were further carried out, indicating that the hexagonal phase in the best performing BaTiO3−x catalyst is oxygen-deficient with a stoichiometry of BaTiO2.76. The oxygen vacancies in the perovskite crystal structure may lead to vastly enhanced electrocatalytic activity toward the ORR and OER. This work demonstrates a new type of highly efficient perovskite bifunctional catalyst for electrochemical energy technologies relying on oxygen electrocatalysis.

Hydration thermodynamics of the proton conducting oxygen-deficient perovskite series BaTi1-xMxO3-x/2 with M = In or Sc.

This article establishes the effect of structure and composition on water uptake and the hydration and proton transport properties of the oxygen-deficient perovskite series BaTi1-x(In,Sc)xO3-x/2, with 0.2 ≤ x ≤ 0.7. The equilibrium water uptake is determined by thermogravimetry, while combining thermogravimetry with differential scanning calorimetry allows for direct determination of the materials' hydration thermodynamics. Proton and oxide ion transport properties are characterized by means of ac impedance measurements up to 1000 °C. In general, the hydration thermodynamics of the scandates are more favorable than that of the indates and are also affected by changes in crystal structure throughout the series. The more favorable hydration thermodynamics of cubic scandates increase their proton conductivity at higher temperatures compared to their indate counterparts. In contrast to the BaTi1-xInxO3-x/2 series, the BaTi1-xScxO3-x/2 (0.5 ≤ x ≤ 0.7) materials retain their cubic structures upon full saturation by protons and show no signs of chemical instability upon exposure to 1 atm H2O(g) down to 100 °C. The BaTi1-xScxO3-x/2 materials with 0.5 ≤ x ≤ 0.7 may therefore find application in, for instance, steam electrolysis or similar processes involving high water vapor pressures.

Redox activity of surface oxygen anions in oxygen-deficient perovskite oxides during electrochemical reactions

Surface redox-active centres in transition-metal oxides play a key role in determining the efficacy of electrocatalysts. The extreme sensitivity of surface redox states to temperatures, to gas pressures and to electrochemical reaction conditions renders them difficult to investigate by conventional surface-science techniques. Here we report the direct observation of surface redox processes by surface-sensitive, operando X-ray absorption spectroscopy using thin-film iron and cobalt perovskite oxides as model electrodes for elevated-temperature oxygen incorporation and evolution reactions. In contrast to the conventional view that the transition metal cations are the dominant redox-active centres, we find that the oxygen anions near the surface are a significant redox partner to molecular oxygen due to the strong hybridization between oxygen 2p and transition metal 3d electronic states. We propose that a narrow electronic state of significant oxygen 2p character near the Fermi level exchanges electrons with the oxygen adsorbates. This result highlights the importance of surface anion-redox chemistry in oxygen-deficient transition-metal oxides.

Oxygen deficient layered double perovskite as an active cathode for CO2 electrolysis using a solid oxide conductor.

A-site ordered PrBaMn2O(5+δ) was investigated as a potential cathode for CO2 electrolysis using a La(0.9)Sr(0.1)Ga(0.8)Mg(0.2)O3 (LSGM) electrolyte. The A-site ordered layered double perovskite, PrBaMn2O(5+δ), was found to enhance electrocatalytic activity for CO2 reduction on the cathode side since it supports mixed valent transition metal cations such as Mn, which could provide high electrical conductivity and maintain a large oxygen vacancy content, contributing to fast oxygen ion diffusion. It was found that during the oxidation of the reduced PrBaMn2O(5+δ) (O5 phase) to PrBaMn2O(6-δ) (O6 phase), a reversible oxygen switchover in the lattice takes place. In addition, here the successful CO2 electrolysis was measured in LSGM electrolyte with this novel oxide electrode. It was found that this PrBaMn2O(5+δ), layered perovskite cathode exhibits a performance with a current density of 0.85 A cm(-2) at 1.5 V and 850 °C and the electrochemical properties were also evaluated by impedance spectroscopy.