Proton-conducting Perovskites Research Articles

Co-doping effect on the microstructural and electrical properties of barium stannate materials

Proton-conducting perovskite oxides are of considerable interest to researchers as promising electrolytes for low- and intermediate solid oxide electrochemical cells. Therefore, designing new potential proton-conducting phases and improving the functional properties of known materials are of great importance from both fundamental and applied viewpoints. In the present work, BaSnO3 was selected as a reference proton-conducting system and then a co-doping strategy was employed to analyze ‘composition – structure – microstructure – transport properties’ relationships. To perform such an analysis, the properties of previously studied BaSn0.7M0.3O3–δ (M = In, Sc, Y) compounds were compared here to their co-doped derivatives, BaSn0.7In0.15Sc0.15O3–δ, BaSn0.7Y0.15Sc0.15O3–δ, and BaSn0.7In0.15Y0.15O3–δ. It is found that the type of dopant affects the materials sinterability, when more coarse-crystalline ceramics are formed with increasing the average ionic radii at the Sn-position. The introduction of Y3+-cations reduces both ionic and hole conductivities compared to single-doped with In3+ or Sc3+ barium stannate materials. However, simultaneous doping with In3+/Sc3+ cations minimizes the contribution of hole conductivity compared to that of Sc-doped barium stannate with the same acceptor dopant concentration.

Growth of proton conducting strontium cerate composites

The increased population and modern way of life have greatly depleted the effectiveness of traditional energy production methods. There is a strong demand for environmentally friendly and renewable alternatives to replace the old systems. Sustainable energy production systems have emerged as a vital replacement for the conventional use of fossil fuels. Among these, solid oxide fuel cells (SOFCs) play a significant role. Recently, researchers have developed electrolyte components for SOFCs using proton-conducting perovskites with excellent conductivity. This critical assessment presents a yearly overview of innovative strategies for utilizing doped strontium cerate perovskites in energy production systems, a novel approach. The importance of identifying dopants that can enhance conductivity and stability in strontium cerate composites is emphasized, creating a crucial element for high-performance energy systems. Through a comparative study, it's been found that rare earth elements with smaller ionic radii, such as thulium-doped strontium cerium zirconate in an additional composite form, can outperform the traditionally used ytterbium-doped strontium cerate composites in proton-conducting applications.

Machine Learning-Assisted Discovery of High-Performance Perovskite Electrolytes for Intermediate-Temperature Protonic Ceramic Electrochemical Cells

Solid oxide electrochemical cells (SOECs) have attracted intensive attention because of their high efficiency and low environmental impact. Much effort has been made to decrease the operating temperature of SOECs down to the intermediate-temperature range. The electrolyte materials with high ionic conductivity are the crucial factor in deciding the operating temperature of SOECs among all components. Proton-conducting perovskite oxides are one of the most promising electrolyte materials for intermediate-temperature SOECs due to their excellent ionic conductivity, usually called protonic ceramic electrochemical cells (PCECs). The most common method to discover the new potential proton-conducting perovskite electrolytes is that the introduced aliovalent dopants facilitate the creation of oxygen vacancy to maintain electroneutrality and give rise to protonic defects when exposed to a reduced atmosphere. In addition to the dopant elements and the dopant content, the total conductivities of doped perovskite electrolytes also depend on the synthesis conditions, the measurement condition and so on. Therefore, the investigation of potential perovskite electrolytes for the intermediate-temperature range should not only be based on the search for the most promising compositions but also requires a detailed study of the influences of its microstructure and processing conditions on the total conductivities. The traditional models of trial-and-error experimental processes limit the development of promising electrolyte materials. Machine learning has emerged as a powerful tool to gain hidden rules from extensive data. By focusing on the investigation of the potential perovskite electrolytes, we collected 400 training data and defined 34 desirable features. Features related to basic elemental properties, crystal structure, microstructure, synthesis conditions, and measurement conditions have been included. Based on these data from the published literature, machine learning models are utilized to predict the total conductivity of perovskite compositions at targeted conditions. Thereafter, feature importance is evaluated to establish a guideline for the rapid and accurate screening of potential perovskite electrolytes in the intermediate-temperature range. Consequently, the screened compositions with high total conductivity from the trained model are prepared, and the experimental results are consistent with the predicted results. This study establishes a new avenue to discover perovskite electrolytes with high total conductivity for intermediate-temperature PCECs. Keywords: Perovskite electrolyte, Proton conducting, Protonic ceramic cells, Machine learning. Figure 1

Benchmarking the yttrium content in the low temperature/low humidity electrical properties of yttrium-doped barium cerate

Yttrium-doped barium cerate (BCY) is one of the best proton-conducting ceramics to be used in fuel cells/electrolyzers at intermediate temperatures, due to its high hydration enthalpy and high conductivity. Nonetheless, it has commonly been discarded for these applications due to its instability in the presence of carbonaceous and humidified atmospheres. A recent work has addressed this issue, by suggesting the use of this material in very low water vapor partial pressures (pH2O ∼ 10−4 atm) [Electrochimica Acta 334 (2020) 135625] and at low temperatures (T ≤ 400 °C). Under these conditions, BCY can still offer pure protonic conductivity while also offering suitable stability. In the current work, we provide a comprehensive analysis of the effects of the acceptor dopant concentration (Y2O3) in the structural, microstructural, and electrical properties in a wide compositional series of BaCe1-xYxO3-δ (x = 0.05, 0.10, 0.20 and 0.30) at low levels of humidity in the low temperature range (100–400 °C). The results show that BaCe0.9Y0.1O3-δ (BCY10) offers the highest bulk conductivity in these conditions, while further increase in dopant concentration leads to impairment due to “proton trapping” effects. In contrast, the specific grain boundary conductivity increases with increasing dopant concentration due to a reduction of Schottky barrier height at the space-charge layer. We demonstrate that, by operating at very low temperatures (e.g., below 400 °C), the peak performing, BCY10 material can still operate at very low levels of water vapor partial pressure (pH2O ∼ 10−4 atm), where its stability can be maintained. This work paves the way for the optimization of this material, with a focus on utilizing low humidity levels and low temperatures, where it can offer a competitive advantage over that of the majority of other proton-conducting perovskites for potential applications operating under these conditions.

Barium cerate and its composite perovskites – synthesis techniques: a comprehensive review

Perovskites have attracted growing interest in recent eras due to their unique properties and potential applications. Barium cerate (BC) proton-conducting perovskites have been examined over decades for various applications such as hydrogen sensors, fuel cells, proton separation membranes, etc. When compared with oxide ion conductors under the same circumstances, ceramic proton conducting barium cerate can diminish the working temperature of solid oxide fuel cells to an intermediate temperature range, 673–873 K because of their higher ionic conduction. The present review carefully analyses and summarizes different synthesis approaches with optimization conditions to prepare BC-derived perovskites and the reported data have been carefully analyzed. A range of synthesis methods such as solid-state reaction method and wet chemical processes like coprecipitation, combustion, Pechini method, etc., have been systematically investigated. Even though the solid-state method has considerable disadvantages, most researchers avoid its incompetence due to the easiness of processing. Applications of the material have been briefly deliberated to exemplify its technological importance. The present review concluded with the recent signs of progress and innovative techniques employed to overcome the processing complications in these materials.

Proton uptake and proton distribution in perovskite materials for protonic ceramic fuel cell applications

Protonic ceramic fuel cells can generate electric power directly by converting the chemical energy stored in fuels through electrochemical reactions, offering a great potential for practical applications due to their high efficiency, low emissions and fuel flexibility. Lower and intermediate working temperatures (400–700 °C) are prerequisites for the commercialization, but inefficient proton uptake and the conduction ability of electrolyte and cathode materials limits the output performance. In this review, we summarize the common methods used to detect the proton concentration and distribution in some typical proton-conducting perovskites. The infrared absorption and Raman spectra combined with the first-principle calculations could provide the most information about hydrogen bond types with vibrational frequencies at 1000–4500 cm<sup>-1</sup>, the local proton environment and interactions between proton and crystal defects. The protons in a symmetric environment are easier to transport in the structure compared with that in an asymmetrical and trapped environment. A good understanding of proton uptake and proton distribution features in perovskite materials is necessary to design suitable proton-conducting materials.<br> The bibliography includes 167 references.

Accelerated Discovery of Proton-Conducting Perovskites through Density Functional Theory and Machine Learning

Hydrogen is an important energy carrier resource in response to limiting greenhouse gas emissions. Proton-conducting perovskite oxide is one of the key materials for highly efficient carbon-neutral hydrogen technologies, such as hydrogen production, CO2 hydrogenation, and ammonia synthesis. Many attempts have been made based on doped perovskites made of well-tested materials, such as BaZrO3, BaCeO3, BaHfO3, BaTiO3, and SrZrO3. However, the resulting perovskites have often suffered stability and conductivity problems. Furthermore, complex phenomena occurring during hydration present challenges for expanding the materials library. Herein, we demonstrate accelerated discovery of proton-conducting perovskites with high conductivity using machine learning (ML) predictions. We constructed consistent training data using density functional theory (DFT) which enable high accuracy of ML model. DFT computations were performed on > 1000 doped perovskite compositions to get their properties of lattice parameters, point defects (e.g., O vacancies, H interstitials), density of states, hydration energy, and proton migration energy. Several ML algorithms including Linear Regression, Bayesian Ridge Regression, Random Forest Regression, Neural networks, and k-Nearest Neighbor were tested for minimum errors and coefficient of determination. The multidimensional relationships between a set of >50 features and conductivity were mapped out using the optimized ML model. We screened a large material space of A-site and B-site doped perovskites to predict potential proton-conducting materials for various energy applications. The outcomes are promising for accelerating the design and applications of proton-conducting perovskite oxides in hydrogen technologies.

Proton Conduction in Acceptor-Doped BaSnO3: The Impact of the Interaction between Ionic Defects and Acceptor Impurities.

Barium stannate is known as a promising proton-conducting material for clean energy applications. In this work, we elucidate the effect of the interaction of protons and oxygen vacancies with acceptor impurities on proton conduction in acceptor-doped BaSnO3. The analysis relies on our theoretical developments in hydration and proton hopping in proton-conducting perovskites. The transport theory, based on the master equation and effective medium approximation, provides the analytical description of hopping conduction considering the effects of disorder and changes in the potential energy landscape for protons caused by acceptor impurities. Using the proposed approach, we establish the dependence of the proton mobility and conductivity on the energies of the acceptor-bound states of ionic defects and external conditions. It is shown that the considered interactions can substantially affect the effective activation energies and prefactors of these transport coefficients. We also demonstrate that the correlation between the ionic radius rA of an acceptor impurity and the energies of its interaction with ionic defects leads to a non-monotonic dependence of the proton conductivity on rA. The obtained results are in reasonable agreement with the experimental data on the bulk conductivity of BaSnO3 doped with different acceptors.

(Digital Presentation) Electrochemical Sensors for Hydrogen/Deuterium Speciation

By the end of the century, global energy demand is expected to increase by a factor of three due to population growth. In this context, fossil fuels should not be the main power source due to the elevated environmental cost. Nuclear fusion technology is planned as an alternative to this demand as it is expected to generate large quantities of energy without all the inconveniences of fossil fuels. The most feasible reaction to take place is the fusion between two hydrogen nuclei. Specifically, deuterium and tritium will react releasing helium, neutrons, and large amounts of energy [1]. 2H + 3H → 4He + n + 17.59 MeV (1)In the present work, BaCe0.6Zr0.3Y0.1O3-α electrolyte (BCZY) was used to construct amperometric sensors for hydrogen monitoring. Firstly, BCZY powder was synthesized by the solid-state method and characterized using SEM and XRD. Secondly, it was sintered as a pellet and bound to an alumina tube to construct the electrochemical sensors. Finally, amperometric measurements were performed inside a stainless-steel reactor at 500 °C and applying 0.15 V between electrodes. The response of the sensors was evaluated using hydrogen and deuterium calibration mixtures. The concentration in the WE ranged from 150 to 300 ppm H2 or D2 in Ar. Argon was used in the CE as a cover gas. Finally, measurements with hydrogen and deuterium were compared to determine the isotope effect on the response.[1] J.Kenneth. Shultis, R.E. Faw, Fundamentals of nuclear science and engineering, Marcel Dekker, 2002.[2] E.C.C. de Souza, R. Muccillo, Properties and applications of perovskite proton conductors, Materials Research. 13 (2010) 385–394. https://doi.org/10.1590/S1516-14392010000300018.[3] A. Benes, A. Molinari, R. Witte, R. Kruk, J. Brötz, R. Chellali, H. Hahn, O. Clemens, Proton Conduction in Grain-Boundary-Free Oxygen-Deficient BaFeO2.5+δ Thin Films, Materials. 11 (2017) 52. https://doi.org/10.3390/ma11010052.[4] A. Hinojo, I. Soriano, J. Abellà, S. Colominas, Evaluation of High-Temperature Hydrogen Sensors Based on BaCe0.6Zr0.3Y0.1O3-α and Sr(Ce0.9Zr0.1)0.95Yb0.05O3-α Perovskites for Industrial Applications, Sensors. 20 (2020) 7258. https://doi.org/10.3390/s20247258.

Dehydrogenation Coupling of Methane Using Catalyst-Loaded Proton-Conducting Perovskite Hollow Fiber Membranes.

Catalytic dehydrogenation coupling of methane (DCM) represents an effective way to convert natural gas to more useful C2 products (C2H6, C2H4). In this work, BaCe0.85Tb0.05Co0.1O3−δ (BCTCo) perovskite hollow fiber membranes were fabricated by the combined phase inversion and sintering method. SrCe0.95Yb0.05O3−δ (SCYb) perovskite oxide was loaded as a catalyst onto the inner hollow fiber membrane surface, which promoted the CH4 conversion and the C2 hydrocarbon selectivity during the DCM reaction. The introduction of steam into the methane feed gas mixture elevated the C2 selectivity and yield due to the alleviation of coke deposition. Switching N2 to air as the sweep gas further increased the C2 selectivity and yield. However, the conversion of methane was limited by both the low permeability of the membrane and the insufficient catalytic activity of the catalyst, leading to low C2 yield.

Preparation and conductive properties of double perovskite oxides Ba3Ba1+xTa2-xO9-δ

In this work, Ba3Ba1+xTa2-xO9-δ (x = 0, 0.1, 0.3, and 0.5) double perovskite proton conductors were prepared by solid-state reaction process. Phase compositions and microstructures were characterized by X-ray diffraction and field emission scanning electron microscope techniques. valence and semi-quantitative composition of components were identified by X-ray photoelectron spectroscopy. Conductivities of Ba3Ba1+xTa2-xO9-δ were then measured under various vapor and oxygen pressures by AC impedance spectroscopy technique. Results revealed linear increase in total conductivities of Ba3Ba1+xTa2-xO9-δ oxides as a function of temperature. Ba3Ba1.3Ta1.7O8.55 exhibited the highest total conductivity of 8.41 × 10−4 S cm−1 under humidity and 800 °C. The transport numbers calculated by defect equilibria model revealed. Ba3Ba1+xTa2-xO9-δ oxides as pure proton conductors at 400–800 °C. Also, transport numbers of oxide ions and holes both increased with temperature. Ba3Ba1.3Ta1.7O8.55 illustrated the highest protonic transport number of 0.60 at 800 °C. In sum, these results suggest that Ba3Ba1+xTa2-xO9-δ oxides display excellent proton conductivity.

Development and application of lanthanum tungstate series proton conductors

<p indent=0mm>As one of the most important clean energy and commodity chemicals, hydrogen is widely used in human life and industrial production. In the present decade, three main technologies for hydrogen recovery have been developed, namely pressure swing adsorption (PSA), cryogenic separation, and membrane separation. Among these three different hydrogen recovery technologies, the membrane separation method is favored for its high efficiency. Benefiting from its absolute selectivity of hydrogen and the low cost, mixed protonic-electronic conductors (MPEC) have become an important research object in the field of hydrogen separation membrane materials, which enable a significant approach for the purification and utilization of hydrogen energy. For the traditional proton-conducting perovskite oxides doped with Ce and Zr, although they have high proton conductivity, their poor chemical stability under the atmosphere in the presence of CO₂ and H₂O hinders the commercial application. Rare-earth metal compound lanthanum tungstate material (LWO) is a kind of crucial proton conductor, which has good chemical stability in CO₂ atmosphere. However, the hydrogen permeability of LWO is not satisfactory because of the low electronic conductivity. A variety of effective methods to improve the hydrogen permeability of lanthanum tungstate film are summarized in this review. This review introduces the basic electronic conductivity of LWO-based single-phase materials, with the emphasis on improving the electronic conductivity of LWO by adjusting La/W ratio, cation doping strategies, and preparation methods. Furthermore, it reviews breakthroughs in their application in proton-conducting solid oxide fuel cells (SOFC) as well as hydrogen separation membranes. The problems now faced by LWO oxides are analyzed and their future development is predicted. Firstly, the proton conductivity of LWO is positively correlated with the La/W ratio. Adjusting the La/W ratio improves proton conductivity of LWO. For cation doping, the substitution of W rather than La more effectively improves the proton conductivity of LWO. Secondly, compositing LWO and the electronic conductors effectively enhance the performance of the hydrogen permeation membranes. Thirdly, in terms of the SOFC applications, an additional oxide layer between the LWO electrolyte layer and the electrode layer avoids the phase reaction on the interface, which prevents the chemical incompatibility between the LWO and electrode materials. Many studies show that the maximum utilization of LWO can be realized by optimizing crystal structure, phase composition, and the SOFC structure. In view of the problems existing in the research of LWO materials, future research can be focused on the following aspects: (1) Further exploring the electronic-ionic conducting pathway and catalytic mechanism of LWO series materials, and then optimizing the electrochemical properties under the guidance. (2) Developing the electrode materials with good catalytic performance and good chemical compatibility with LWO which is significant to the stable operation of SOFC. Also, it is necessary to improve the cell preparation process in which the unbeneficial interface reaction between the electrode and the LWO can be avoided. (3) For hydrogen permeation membrane, future research can be developed towards optimization with cation doping, surface engineering, and composite materials preparation.

Accelerated Discovery of Proton-Conducting Perovskite Oxide by Capturing Physicochemical Fundamentals of Hydration

Accelerated Discovery of Proton-Conducting Perovskite Oxide by Capturing Physicochemical Fundamentals of Hydration

Effect of the addition mechanism of ZnO sintering aid on densification, microstructure and electrical properties of Ba(Zr,Y)O3-δ proton-conducting perovskite

We explore three different potential mechanisms to introduce 4 mol% ZnO sintering additive to the promising yttrium-doped barium zirconate (Ba(Zr,Y)O3-δ, BZY) proton conductor. The mechanisms involve Zn substitution for Y, Zr, or B-site cation excess. The addition of ZnO promotes high densification levels (up to 98% of the theoretical value) at 1300 °C, irrespective of the mechanism. However, scanning electron microscopy shows that the B-site cation excess mechanism leads to an impaired grain growth compared to the other mechanisms. Rietveld refinement of the lattice-parameters and scanning transmission electron microscopy-energy dispersive X-ray spectroscopy indicates that Zn resides in both grains and grain boundaries in all cases. Determination of partial conductivities demonstrates that the Zr substitution mechanism provides slightly higher values of bulk protonic conductivity, as well as a higher hydration enthalpy. In contrast, the B-site excess mechanism provides the highest specific grain-boundary conductivity, as a result of greater Zn segregation to the grain boundary.

Proton‐Conducting Fuel Cells: A New Pd Doped Proton Conducting Perovskite Oxide with Multiple Functionalities for Efficient and Stable Power Generation from Ammonia at Reduced Temperatures (Adv. Energy Mater. 19/2021)

In article number 2003916, Guangming Yang, Zongping Shao and co-workers investigate a new Pd doped BaZr0.1Ce0.7Y0.1Yb0.1O3−δ as an anode component and electrolyte, which boosts the activity of anodes for NH3 decomposition, and increases proton conductivity and sintering of electrolytes. The NH3-fueled proton-conducting fuel cell delivers superior power density and stability, making it highly promising for practical applications.

Diffusional Dynamics of Hydride Ions in the Layered Oxyhydride SrVO2H.

Perovskite-type oxyhydrides are hydride-ion-conducting materials of promise for several types of technological applications; however, the conductivity is often too low for practical use and, on a fundamental level, the mechanism of hydride-ion diffusion remains unclear. Here, we, with the use of neutron scattering techniques, investigate the diffusional dynamics of hydride ions in the layered perovskite-type oxyhydride SrVO2H. By monitoring the intensity of the elastically scattered neutrons upon heating the sample from 100 to 430 K, we establish an onset temperature for diffusional hydride-ion dynamics at about 250 K. Above this temperature, the hydride ions are shown to exhibit two-dimensional diffusion restricted to the hydride-ion sublattice of SrVO2H and that occurs as a series of jumps of a hydride ion to a neighboring hydride-ion vacancy, with an enhanced rate for backward jumps due to correlation effects. Analysis of the temperature dependence of the neutron scattering data shows that the localized jumps of hydride ions are featured by a mean residence time of the order of 10 ps with an activation energy of 0.1 eV. The long-range diffusion of hydride ions occurs on the timescale of 1 ns and with an activation energy of 0.2 eV. The hydride-ion diffusion coefficient is found to be of the order of 1 × 10–6 cm2 s–1 in the temperature range of 300–430 K, which is similar to other oxyhydrides but higher than for proton-conducting perovskite analogues. Tuning of the hydride-ion vacancy concentration in SrVO2H thus represents a promising gateway to improve the ionic conductivity of this already highly hydride-ion-conducting material.

A New Pd Doped Proton Conducting Perovskite Oxide with Multiple Functionalities for Efficient and Stable Power Generation from Ammonia at Reduced Temperatures

AbstractThe combination of ammonia fuel and proton‐conducting fuel cells (PCFCs) technology may provide an ideal clean energy system for the future, considering matured NH3 synthesis technology and transportation and storage infrastructure, the high energy density of NH3, and the high efficiency of fuel cells. However, poor catalytic activity of the anode for NH3 decomposition, quick performance degradation due to the ammonia induced nickel coarsening, difficult sintering, and insufficient proton conductivity of electrolytes are the main challenges for stable and high‐power generation from ammonia‐fueled PCFCs. Herein, a new Ba(Zr0.1Ce0.7Y0.1Yb0.1)0.95Pd0.05O3−δ perovskite is reported as a key anode component and electrolyte, which demonstrates multifunctionalities and tackles most challenges of conventional PCFCs. The incorporation of a small amount of Pd boosts catalytic activity of the nickel‐perovskite cermet anode for NH3 decomposition and increases proton conductivity from the creation of B‐site cation deficiency and electrolyte sintering. The corresponding thin‐film electrolyte PCFC delivers a maximum power density of 724 mW cm–2 at 650 °C operated on NH3, much higher than the similar cell without Pd incorporation (450 mW cm–2). Furthermore, no apparent performance decay is observed for the cell operated at 550 °C in H2 and NH3 for 350 h, making it highly promising for practical applications.

Enhanced proton conductivity and stability of Ba-deficient BaCe0.8Y0.2O3-δ

A-cation deficiency has a significant impact on the properties of proton-conducting perovskites (ABO3), depending on factors such as the ionic radius, concentration of dopant and degree of substoichiometry of the A-site cation. Here, we focus on the influence of Ba deficiency on the structure, stability and partial electrical conductivities of the perovskite BaCe0.8Y0.2O3-δ (BCY20). Neutron powder diffraction is employed to determine a monoclinic symmetry (space group I2/m) for Ba0.95Ce0.8Y0.2O3-δ (B95CY20), with greater distortion and specific free volume than BCY20. Confocal Raman microscopy integrated with atomic force microscopy and X-ray diffraction confirm improved resistance to carbonate formation in the Ba-deficient material. Electrical conductivity is also greater for B95CY20 in both wet and dry oxidising and moderate reducing conditions, reaching ≈1.4 and 1 S m−1 in dry conditions of O2 and N2, respectively, at 600 °C. Partial conductivities determined by a defect-chemistry-based method indicate that proton conductivity is dominant in wet air for temperatures <700 °C and greater for B95CY20 (≈0.95 S m−1 at 600 °C) in comparison to BCY20 (≈0.58 S m−1 at 600 °C), with an associated hydration enthalpy of −128 kJ mol−1. Mixed oxide ionic-electronic conductivity dominates in dry oxidising conditions and, again, is greater for Ba substoichiometric material.

Non-stoichiometry, structure and properties of proton-conducting perovskite oxides

The demand for clean and sustainable energy has garnered great interest in new energy materials. Among them, high temperature proton-conducting perovskite oxides are, or can be widely used in clean energy applications (including fuel cells, electrochemical reactors, solid-state separators and supports of catalytic components via various reduction and oxidation reactions) in the intermediate temperature range. The control of defect chemistry is the main strategy to fine tune properties for these applications. This review provides a critical discussion about non-stoichiometry-structure-property relation in terms of structure distortions by intrinsic octahedral titling and extrinsic acceptor doping, chemical stability, hydration behavior, transport properties, and catalytic effects in some typical classes of proton conducting perovskites and perovskite-related derivatives. A good understanding of A-site and B-site non-stoichiometry is also given to allow the perovskite structure with desired properties.

Determination of Oxide Ion Conductivity in Ba-Doped LaYbO3 Proton-Conducting Perovskites via an Oxygen Isotope Exchange Method

Proton-conducting oxides have garnered much attention as electrolyte materials of electrochemical devices operating at intermediate temperatures ranging 400–700 °C. For the implementation, quantifying the transport number of oxygen ions is crucial to predict the fuel utilization efficiency of solid oxide fuel cells (SOFCs). The acceptor-doped LaYbO3 proton conductors are one of the candidates for the electrolyte material of electrochemical devices such as SOFCs because of their high pure proton conduction. However, the oxide ion conductivity in this material is not quantified yet. Here, we evaluate the tracer diffusion coefficient (D*) of 5 mol % Ba-doped LaYbO3 by the oxygen isotope exchange and depth profile technique using secondary ion mass spectrometry. It is found that the oxygen ion conductivities in this material are lower than 10–4 S cm–1 below 800 °C, less than 2% to the total conductivity. We also visualize the domain of dominant conduction in this material. It reveals that proton conduction is dominant in fairly wide areas of the atmospheric condition, in particular below 600 °C, suggesting that the Ba-doped LaYbO3 is suitable for the SOFC electrolyte in terms of transport number.