High Oxygen Ion Conductivity Research Articles

Computational discovery of fast interstitial oxygen conductors.

New highly oxygen-active materials may enhance many energy-related technologies by enabling efficient oxygen-ion transport at lower temperatures, for example, below ~400 °C. Interstitial oxygen conductors have the potential to realize such performance but have received far less attention than vacancy-mediated conductors. Here we combine physically motivated structure and property descriptors, ab initio simulations and experiments to demonstrate an approach to discover new fast interstitial oxygen conductors. Multiple new families were found, which adopt completely different structures from known oxygen conductors. From these families, we synthesized and studied oxygen kinetics in La4Mn5Si4O22+δ, a representative member of the perrierite/chevkinite family. We found that La4Mn5Si4O22+δ has higher oxygen-ion conductivity than the widely used yttria-stabilized ZrO2, and among the highest surface oxygen exchange rates at the intermediate temperature of known materials. The fast oxygen kinetics is the result of simultaneously active interstitial and interstitialcy diffusion pathways. We propose that the essential features for forming an effective interstitial oxygen conductor are the availability of electrons and structural flexibility, enabling a sufficient accessible volume. This work provides a powerful approach for understanding and discovering new interstitial oxygen conductors.

Spectroscopic Elucidation of Phase Evolution in NiO/YSZ Under Oxidative and Reductive Gas Environments

High temperature co-electrolysis of CO2 and H2O serves a viable, energy efficient, and scalable route to produce syngas (CO+ H2), which can be used to generate a variety of utility hydrocarbons. Solid oxide electrolysis cell (SOEC) has proven to be a promising technology for CO2 utilization and a carbon neutral route to curb CO2 emissions. The design of cathode catalyst is critical as it must facilitate the activation of CO2 and H2O and also exhibit high electronic and oxygen ion conductivity. The state-of-the-art cathode material used in SOECs is Ni/YSZ (8 mol% Yttria Stabilized Zirconia) ceramic composite (known as cermet), whose performance is dependent on various operating factors including temperature, composition of feed gas stream, presence of contaminants like SOx/NOx etc. There is a very limited number of studies on the evolution of the cathode materials under process level conditions. To begin with, effect of different oxidative and reductive gas environments and temperature over Ni/YSZ is studied using in situ Raman spectroscopy.Typical flue gas composition is chosen as the basis for the concentration of different components like 15% CO2, 10% H2O, 5% O2 with argon. Under oxidative conditions (O2, CO2, H2O) with temperature variation range of RT-800 0C, NiO/YSZ vibrational modes revealed that it is composed of NiO and YSZ phases. It is seen that there is thermal broadening in the bands of NiO and YSZ, thermal effects reversible upon cooling down and red shift in the NiO bands exemplified the lattice expansion. Exposing the NiO/YSZ to 5% H2 at high temperature resulted in the formation of metallic Ni, which is corroborated by the absence of the Ni-O vibrational modes in Raman spectrum at 400 0C. YSZ phase is quite stable in H2 at elevated temperature.After reduction of NiO/YSZ to get Ni/YSZ, exposure to oxidative environments (i.e., O2, CO2, H2O) aided in the formation of defect laden NiOx phase on YSZ. Specifically, NiOx formation starts at 350 0C under oxygen and at 450 0C under CO2 and H2O. Under 15% CO2, there is an overlap between the bands associated to the carbonate like species and the NiO phase but there is no formation of coke at these conditions as D and G bands were not observed (Fig. 1). It could be due to the oxidation of Ni that obliterated coke formation. The blue shift at 1046 cm-1 (2P mode of NiO) signifies the shortening of bond length in Ni-O with gradual conversion of Ni to NiOx. Compared to the NiOx phase formed under 5% O2 and 15% CO2 which has a sharp feature in Raman spectra, there is a broad band of NiOx phase formed under 10 % H2O in the region 480-580 cm-1 . This observation demonstrates the variation in the microcrystalline size of the defect laden NiOx phase formed under exposure to different oxidizers.Another set of experiments were done with the dry hydrogen (5 % H2) and humidified hydrogen (5% H2 + 10 % H2O) to study the role of presence of water on the reduction of NiO/YSZ with temperature variation between 120 – 800 0C. It was found that reduction of NiO to Ni is not affected by the presence of water. Under both conditions this transformation occurs between 400-600 0C. The results from the current study provide the key information on the effects of temperature and gas compositions over Ni/YSZ which serves as a guide for the process level design and operation of SOECs. References Juliana Carneiro et al, Industrial & Engineering Chemistry Research 2020 59(36), 15884-15893.John Kirtley et al, The Journal of Physical Chemistry C2013, 117 (49), 25908-25916.A. Naumenko et al, Phys Chem Solid State 2008, 9, 121–125. Figure 1

La0.8Sr0.2Ga0.8Mg0.2O3−δ − molten carbonate membrane for high − temperature CO2 separation

A perovskite structure La0.8Sr0.2Ga0.8Mg0.2O3−δ (LSGM), is a promising support material for dual − phase membrane for high − temperature CO2 separation owing to its high oxygen ion conductivity. The microstructure plays an important role in CO2 separation performance of the membrane. The result shows that effective particle − to − particle contact is a crucial guarantee for improving CO2 permeability. The uniformly distributed small pores of the support can greatly reduce the leakage. The Al2O3 coating on the porous support can improve the wettability between LSGM and molten carbonate, simultaneously increasing CO2 permeation flux while reducing leakage. The Al2O3 coated LSGM − based dual − phase membrane achieves a CO2 permeation flux of 0.34 mL min−1 cm−2 at 750 °C, with no detectable leakage. Above 750 °C, a reaction occurs between LSGM and molten carbonate, leading to a decline in membrane performance. For LSGM − carbonate dual − phase membranes, it is recommended to operate at temperatures not exceeding 750 °C.

Cu2+ and W6+ co-doped Na0·5Bi0·5TiO3 solid solution: An effective approach to inhibit oxygen vacancy generation and suppress oxygen ion conduction

Thanks to its outstanding features, the Na0·5Bi0·5TiO3 is a promising as a dielectric material for various advanced electronic devices. However, its high oxygen ionic conductivity and wide band-gap energy pose limitations on its suitability for commercial applications. In this work, an approach to inhibit oxygen vacancy generation and suppress oxygen ion conduction is investigated through the B-site donor and acceptor doping strategy. This study aims to investigate the morphological, structural, compositional, dielectric, electric, and optical properties of 0.99NBT-0.01BCW and 0.985NBT-0.015BCW perovskite ceramics. The research also explores the impact of Cu2+ and W6+ substitution on the perovskite structure and its potential applications. Morphological analysis revealed well-defined grains with cubic shapes, influenced by Cu2+ and W6+ incorporation. Structural analysis confirmed a rhombohedral lattice with R3c space group. Dielectric analysis showed ferroelectric to antiferroelectric and antiferroelectric to paraelectric phase transitions, with emphasis on relaxor behavior influenced by BCW doping. Electric analysis demonstrated a semiconductor behavior with activation energies, suggesting inhibited conduction loss at high temperatures due to BCW doping. Optical analysis revealed direct bandgap energies suitable for applications in optoelectronics and photonics. These findings suggest that doping with Cu2+ and W6+ restrains conduction losses at elevated temperatures, potentially serving as the primary mechanism for suppressing the high-temperature dielectric loss in NBT-based ceramics. They highlight the potential of these perovskite ceramics in applications such as capacitors, sensors, and optoelectronic devices.

Field-assisted sintering of refractory oxygen-ion and proton conducting ceramics

Solid oxides with high oxygen-ion and proton conductivity have been extensively studied for applications in electrochemical devices such as fuel cells, electrolyzers, sensors, hydrogen separators, etc. However, the preparation of high-density ceramic electrolytes is often complicated by the exceptional refractoriness of most oxygen-ion conducting solid oxide phases. Therefore, conventional sintering of these materials is very energy consuming and low effective. In recent years, non-conventional field-assisted sintering technologies (FASTs) such as spark plasma sintering, flash sintering and microwave sintering, have been developed and applied for sintering dense ceramic electrolytes at reduced temperatures. In this article, the applications of FASTs for densification of refractory oxygen-ion and proton conducting ceramics are reviewed, while the mechanisms, advantages and limitations of these technologies are discussed, with special emphasis on the effects of FASTs on the microstructural and transport properties of sintered materials, and the performance of FAST-processed electrochemical cells.

Improved La0.8Sr0.2MnO3-δ oxygen electrode activity by introducing high oxygen ion conductor oxide for solid oxide steam electrolysis

The limited oxygen ion conductivity of conventional La0.8Sr0.2MnO3-δ (LSM) electrode has hindered the development of high-performance solid oxide cells. To address this issue, the electrode interface structure of LSM electrode is regulated by incorporating oxides with high oxygen ion conductivity. Specifically, the addition of Dy and Y co-doped Bi2O3-δ oxide (DBY) with a conductivity of 0.34 S cm−1 at 700 °C, which is almost 9 and 20 times higher than conventional SDC and YSZ oxides, has found to substantially reduce the electrode sintering temperature and enhance the transport ability of ion and electron at the interface. As a result, the interface polarization resistance of the LSM/DBY composite electrode is as low as 0.096 Ω cm2 at 700 °C. Finally, a solid oxide cell equipped with an LSM/DBY electrode attains a high power density of 1.78 Wcm−2 in fuel cell mode at 800 °C and 3%H2O–H2, as well as a current density of −1.58 Acm−2 in electrolysis mode under 1.50 V and 50% H2O–H2 condition.

Discovery of New Fast Oxygen Conductors: Bi2MO4x (M= rare earth, X= halogen) Via Unsupervised Machine Learning

Discovering new fast oxygen conductors is critical for developing many technologies, e.g., solid oxide fuel cells (SOFCs), solid oxide electrolysis cells (SOECs), proton ceramic fuel cells (PCFCs), and solid oxide air batteries, particularly for operation at lower temperatures (below 700 ˚C). By leveraging unsupervised machine learning techniques and large databases of computed materials data (e.g., Materials Project), we are able to rapidly explore and screen for new materials with high oxygen mobility. In this work, we used unsupervised machine learning analysis applied to features extracted from the structure of materials and discovered a new structural class of vacancy-mediated oxygen conductor. To do this, we applied the K-nearest neighbor (k-NN) algorithm on all the approximately 62,000 oxygen-containing compounds in the Materials Project database, using X-ray diffraction (XRD) and pair distribution function (PDF) data to represent the structural features. The neighbors of reference known for good oxygen conductors were screened with criteria relating to material stability, synthesizability, and electronic property dissimilarity (to ensure a novel material) compared to the reference material. Starting with the best-known oxygen conductor, the fluorite-type material, we examined the materials list of its nearest neighbors and identified the Bi2MO4X (M=Rare-earth element, X= halogen element) structural family as a novel group of fast oxygen conductors. In particular, Bi2LaO4Cl is a layered bismuth oxyhalide crystallized in the space group P4/mmm, adopting a “triple fluorite” layer [Bi2LaO4]+, balanced by the anion Cl- layer. The stability and mobility of oxygen vacancy in Bi2LaO4Cl were studied using Density Functional Theory (DFT) methods. 2+ oxygen vacancy is the most thermodynamically favorable defect type. Ab initio and machine learning-trained interatomic potential molecular dynamic simulations were performed to study the high temperature oxygen mobility in Bi2LaO4Cl. The simulation results show that Bi2LaO4Cl presents an extremely low migration barrier of 0.14 +/- 0.03 eV below 700 ˚C, suggesting 10 to 20 times higher ionic conductivity compared to yttria-stabilized zirconia (YSZ). Bi2LaO4Cl is an insulator with a wide band gap of 2.65 eV, indicating that Bi2LaO4Cl may be a promising electrolyte material with high oxygen ion conductivity and low electronic conductivity. This work demonstrates the power of combining unsupervised machine learning approaches with large materials databases for finding new fast oxygen conductors.

New Family of Interstitial Oxygen Ion Conductor Discovered By High-Throughput Computational Screening

Discovery and design of highly efficient oxygen-active materials which react with, absorb, and transport oxygen is essential for fuel cells and related applications. Currently, the predominant families of oxygen-active materials used in commercial devices are perovskites and fluorites, which diffuse oxygen via a vacancy mechanism and only have adequate oxygen diffusivity and surface exchange at high temperatures (e.g., ~800 ˚C), impeding their use at lower temperatures desirable for more cost-effective and long-lasting device operation. The development of alternative electrolyte/electrode materials with high oxygen ionic conductivity at low temperatures (e.g., room temperature to 400 °C) is of great interest. Interstitial oxygen ion conductors typically have significantly lower migration barriers than even state-of-the-art vacancy-mediated oxygen conductors, which can provide orders of magnitude kinetic enhancement at low temperatures. In addition, the interstitial oxygen defects typically become more thermodynamically favorable as the temperature is lowered, potentially providing an additional boost to the oxygen conductivity at low temperatures from a higher mediating defect concentration. The synergistic combination of low migration barriers and thermodynamically favorable interstitial oxygen content at low temperatures provides the tantalizing possibility that interstitial oxygen conductors may lead to transformative performance improvements in oxygen-active materials.In this work, we developed an approach to discover new interstitial-mediated oxygen conductors by performing high-throughput computational screening of the 34k oxide materials from the Materials Project database and discovered a new structural family of interstitial oxygen diffusers, perrierite-type oxide La4Mn5Si4O22+ 𝜹 (LMS). We used a hierarchy of screening criteria including the geometric free space, thermodynamic stability, synthesizability, redox-active elements, and presence of short diffusion pathways. This approach, based largely on simple, physically intuitive properties, quickly winnowed the field of 34k oxides down to just 345 oxides, an approximate 99% reduction in the search space considered, with essentially no significant computational cost. From this reduced set of promising materials, ab initio simulations were performed to calculate the interstitial oxygen formation energy and migration energy. Our screening has yielded several material families to date, among which the A4B5C4O22+ 𝜹, with La4Mn5Si4O22+ 𝜹 (LMS) as a representative material, was selected for investigation with higher-fidelity DFT hybrid functional calculations and experimental validations. The calculated formation energy of interstitial oxygen is -0.11 eV at a concentration of 2.3% under air condition, indicating that LMS is predicted to be oxygen hyperstoichiometric with an expected composition of La4Mn5Si4O22+0.5 in air. Two separate interstitial and interstitialcy (“kick-out”) diffusion mechanisms are revealed by ab initio molecular dynamics (AIMD) simulation. For the interstitial diffusion pathway, the moves through the channel in between the zigzag-arranged sorosilicate Si2O7 groups, with a barrier of 0.69 eV. For the interstitialcy diffusion pathway, the moves along the corner-sharing Si2O7-MnO2-Si2O7 framework by kicking out the lattice oxygen, with a barrier of 0.74 eV. These results align well with the experimental findings of stable interstitial oxygen content and high oxygen mobility in LMS (Please see a separate poster from Md Sariful Sheikhfor experimental results). This work provides a systematic approach to screening a large number of prospective materials and opens a new avenue of finding promising interstitial oxide ion conducting materials for potential applications in a range of fast oxygen ion conduction-based technologies.

Deep insights into the Cu- and W-doped Na0.5Bi0.5TiO3 solid solution: A study focusing on optical, dielectric and electrical properties

Na0.5Bi0.5TiO3 ceramic is among the most promising dielectric materials for several advanced electronic devices due its exceptional features. However, its high oxygen ionic conductivity and wide band-gap energy limit its use for commercial applications. Here, a new Lead-free solid solution 0.995(Na0.5Bi0.5TiO3)-0.005(BiCu0.75W0.25O3), abbreviated 0.995NBT-0.005BCW, was investigated to enhance the electrical and optical performance of NBT ceramic. 0.995NBT-0.005BCW was successfully elaborated by the solid-state technique. The structural, optical, dielectric and electric properties were investigated systematically. The incorporation of BCW into NBT improved the long-range order of the structure, facilitated the poling process, enhanced the electrical properties of the pure NBT and led to the local lattice distortion, generating new electronic levels inside the NBT bandgap. The calculated band gap value ∼3 eV suggests its suitability in power electronic devices. The variation of dielectric constant and dielectric loss with temperature (370–800 K) at different frequencies (100–106 Hz) showed diffused phase transition. The study of dc-conductivity suggests that the substitution of Cu2+ for Ti4+ would formCuTi″, which transforms Cu2+ to Cu+. Our compound is a novel material with interesting properties and offers exciting possibilities for engineering and manufacturing applications.

Oxygen–Ion Conductivity, Dielectric Properties and Spectroscopic Characterization of “Stuffed” Tm2(Ti2−xTmx)O7−x/2 (x = 0, 0.1, 0.18, 0.28, 0.74) Pyrochlores

Tm2(Ti2−xTmx)O7−x/2 (x = 0, 0.1, 0.18, 0.28, 0.74) solid electrolytes have been investigated as potential electrolyte materials for solid oxygen fuel cells (SOFCs), operating in the medium temperature range (600–700 °C). The design of new oxygen-conducting materials is of importance for their possible utilization in the solid oxide fuel cells. The oxygen–ion conductivity of the Tm2(Ti2−xTmx)O7−x/2 (x = 0, 0.1, 0.18, 0.28, 0.74) “stuffed” pyrochlores ceramics was investigated by electrochemical impedance spectroscopy (two-probe AC) in dry and wet air. The synthesis of precursors via co-precipitation and the precipitate decomposition temperature have been shown to be of key importance for obtaining dense and highly conductive ceramics. At ~770 °C, the highest total conductivity, ~3.16 × 10−3 S/cm, is offered by Tm2Ti2O7. The conductivity of the fluorite-like solid solution Tm2(Ti2−xTmx)O7−x/2 (x = 0.74) is an order of magnitude lower. However, for the first time a proton contribution of ~5 × 10−5 S/cm at 600 °C has been found in Tm2(Ti2−xTmx)O7−x/2 (x = 0.74) fluorite. Until now, compositions with proton conductivity were not known for the intermediate and heavy rare earth titanates Ln2(Ti2−xLnx)O7−x/2 (Ln = Ho − Lu) systems. The use of X-ray diffraction (structural analysis with Rietveld refinement), optical spectroscopy and dielectric permittivity data allowed us to follow structural disordering in the solid solution series with increasing thulium oxide content. High and low cooling rates have been shown to have different effects on the properties of the ceramics. Slow cooling initiates’ growth of fluorite nanodomains in a pyrochlore matrix. The fabrication of such nanostructured dense composites is a promising direction in the synthesis of highly conductive solid electrolytes for SOFCs. We assume that high-temperature firing of nanophase precursors helps to obtain lightly doped “stuffed” pyrochlores, which also provide the high oxygen–ion conductivity.

Research on the tetragonal phase content and microstructure of microwave-assisted sintering Y-PSZ system doped Bi2O3

Partially stabilized Y2O3–ZrO2 (Y-PSZ) is often used as a material in the field of oxygen sensors and batteries. However, the presence of a tetragonal phase will seriously reduce the conductivity of Y-PSZ materials. As a sintering aid, Bi2O3 can be used to sinter materials with high oxygen ion conductivity at low temperatures. It is the first choice for the Y-PSZ doped system. A new microwave sintering technique prepared Bi2O3–Y-PSZ powders. The effects of doping amount of Bi2O3 on the microstructure, phase transition, and tetragonal phase content of Y-PSZ during sintering were researched. The results displayed that doping Bi2O3 improved the tetragonal phase content of the ZrO2. The tetragonal phase content of the samples increased from 59.72% to 94.69% after sintering at 750 °C for 1 h. After doping Bi2O3, the aggregation of the samples reduced gradually, and the particles dispersed evenly. The average particle sizes of raw material and samples doped with different amounts of Bi2O3 were 0.0794 μm, 0.0638 μm, 0.0629 μm, 0.0794 μm, 0.1116 μm, respectively. Therefore, in the doping amount (1 mol%-4 mol%), the Bi2O3 doped Y-PSZ system with 2 mol% has the highest tetragonal phase content, the best dispersion, the smallest average particle size, and the most uniform particle distribution.

A high performance IT-EOG cell based on a solid/molten Bi2O3–B2O3 composite electrolyte

New electrolytes with high oxygen ionic conductivity are required to realize efficient intermediate temperature electrochemical oxygen generators (IT-EOGs).

Revealing the impact of the voltage-induced interfacial effect on conduction properties of CeO2-based electrolyte: A modeling investigation

As widely used electrolyte materials in intermediate-temperature solid oxide fuel cells, the acceptor-doped CeO2 possesses not only high oxygen-ionic conductivity but also nonnegligible electronic conductivity. It has been experimentally confirmed that the voltage-induced interfacial effect can significantly affect the properties of the CeO2-based electrolyte. However, the voltage-induced interfacial effect is not yet properly treated in modeling studies concerning the charged defect distribution in the CeO2-based electrolyte. In this study, a new mathematical model of mixed oxygen-ionic and electronic conducting electrolyte, considering the voltage-induced interfacial effect upon the charged defect distributions within the electrolyte layer, is built. The mathematical treatment of the model based on the finite element method is clearly presented. The good agreements between the experimental data and model-predicted results at both open-circuit and operation conditions well validate the developed model. The modeling results elucidate that output voltages can significantly affect the distribution of charged defects, particularly for the localized electron, then further influencing its mixed conduction properties and behaviors. The results of this work can provide fundamental insight into the mixed ionic and electronic conducting properties and behaviors of the CeO2-based electrolyte.

Effects of Sintering Parameters on the Low-Temperature Densification of GDC Electrolyte Based on an Orthogonal Experiment

A solid oxide fuel cell is a high-efficiency power device in hydrogen energy utilization. The durability and dynamic performance of metal-supported solid oxide fuel cells (MS-SOFCs) are superior to those of electrolyte- or electrode-supported cells, with many potential applications. Gadolinium-doped cerium (GDC) has a high oxygen ionic conductivity, making it suitable to act as the electrolyte in MS-SOFCs operating at 500–650 °C. However, the low-temperature sintering of GDC is difficult for MS-SOFCs. In this study, the factors affecting the low-temperature densification of GDC are analyzed based on an orthogonal experimental method. The shrinking rates of 16 experiments are determined. The effects of the particle diameter, pressure of the uniaxial press machine, sintering temperature, and fractions of aid and binder are estimated. The results of a range analysis indicate that the content of sintering aid has the greatest impact on the low-temperature densification of GDC, followed by the powder diameter and the uniaxial pressure. A maximum shrinking rate of 46.99% is achieved with a temperature of 1050 °C.

Zirconia- and ceria-based electrolytes for fuel cell applications: critical advancements toward sustainable and clean energy production.

Solid oxide fuel cells (SOFCs) are emerging as energy conversion devices for large-scale electrical power generation because of their high energy conversion efficiency, excellent ability to minimize air pollution, and high fuel flexibility. In this context, this critical review has focussed on the recent advancements in developing a suitable electrolyte for SOFCs which has been required for the commercialization of SOFC technology after emphasizing the literature from the prior studies. In particular, the significant developments in the field of solid oxide electrolytes for SOFCs, particularly zirconia- and ceria-based electrolytes, have been highlighted as important advancements toward the production of sustainable and clean energy. It has been reported that among various electrolyte materials, zirconia-based electrolytes have the potential to be utilized as the electrolyte in SOFC because of their high thermal stability, non-reducing nature, and high mechanical strength, along with acceptable oxygen ion conductivity. However, some studies have proved that the zirconia-based electrolytes are not suitable for low and intermediate-temperature working conditions because of their poor ionic conductivity to below 850°C. On the other hand, ceria-based electrolytes are being investigated at a rapid pace as electrolytes for intermediate and low-temperature SOFCs due to their higher oxygen ion conductivity with good electrode compatibility, especially at lower temperatures than stabilized zirconia. In addition, the most emerging advancements in electrolyte materials have demonstrated that the intermediate temperature SOFCs as next-generation energy conversion technology have great potential for innumerable prospective applications.

Rational design of mixed ionic–electronic conducting membranes for oxygen transport

The mixed ionic–electronic conducting (MIEC) oxides have generated significant research efforts in the scientific community during the last 40 years. Since then, many MIEC compounds, most of which are based on perovskite oxides, have been synthesized and characterized. These compounds, when heated to high temperatures, form solid ceramic membranes with high oxygen ionic and electrical conductivity. The driving force for oxygen ion transport is the ionic transfer of oxygen from the air as a result of the differential partial pressure of oxygen across the membrane. Electronic and ionic transport in a range of MIEC materials has been studied using the defect theory, particularly when dopants are introduced to the compound of interest. As a result, many types of ionic oxygen transport limits exist, each with a distinct phase shift depending on the temperature and partial pressure of oxygen in use. In combination with theoretical principles, this work attempts to evaluate the research community's major and meaningful achievements in this subject throughout the preceding four decades.

The Gd2-xMgxZr2O7-x/2 Solid Solution: Ionic Conductivity and Chemical Stability in the Melt of LiCl-Li2O.

Materials with pyrochlore structure A2B2O7 have attracted considerable attention owing to their various applications as catalysts, sensors, electrolytes, electrodes, and magnets due to the unique crystal structure and thermal stability. At the same time, the possibility of using such materials for electrochemical applications in salt melts has not been studied. This paper presents the new results of obtaining high-density Mg2+-doped ceramics based on Gd2Zr2O7 with pyrochlore structure and comprehensive investigation of the electrical properties and chemical stability in a lithium chloride melt with additives of various concentrations of lithium oxide, performed for the first time. The solid solution of Gd2−xMgxZr2O7−x/2 (0 ≤ x ≤ 0.10) with the pyrochlore structure was obtained by mechanically milling stoichiometric mixtures of the corresponding oxides, followed by annealing at 1500 °C. The lattice parameter changed non-linearly as a result of different mechanisms of Mg2+ incorporation into the Gd2Zr2O7 structure. At low dopant concentrations (x ≤ 0.03) some interstitial positions can be substituted by Mg2+, with further increasing Mg2+-content, the decrease in the lattice parameter occurred due to the substitution of host-ion sites with smaller dopant-ion. High-density ceramics 99% was prepared at T = 1500 °C. According to the results of the measurements of electrical conductivity as a function of oxygen partial pressure, all investigated samples were characterized by the dominant ionic type of conductivity over a wide range of pO2 (1 × 10–18 ≤ pO2 ≤ 0.21 atm) and T < 800 °C. The sample with the composition of x = 0.03 had the highest oxygen-ion conductivity (10−3 S·cm−1 at 600 °C). The investigation of chemical stability of ceramics in the melt of LiCl with 2.5 mas.% Li2O showed that the sample did not react with the melt during the exposed time of one week at the temperature of 650 °C. This result makes it possible to use these materials as oxygen activity sensors in halide melts.

Revealing the impact of acceptor dopant type on the electrical conductivity of sodium bismuth titanate

Solid solutions of sodium bismuth titanate (NBT) belong to the most performant lead-free dielectric ceramics for energy storage. However, the defect chemistry of NBT is very complex, and acceptor doping can lead to an unexpected and extraordinarily high oxygen ionic conductivity. This can be attributed to a non-linear change in the formation of defect associates between acceptor and oxygen vacancy with increasing acceptor doping. Using different acceptor dopants with varying concentrations, we elucidate the interaction between acceptors and oxygen vacancies in this work. With the help of total energy calculations based on density functional theory and molecular dynamics simulations, the experimentally observed differences in conductivity can be rationalized.

Plasma-Sprayed (Bi2O3)0.705 (Er2O3)0.245 (WO3)0.05 Electrolyte for Intermediate-Temperature Solid Oxide Fuel Cells (IT-SOFCs).

Stabilized bismuth oxide material with fluorite structure (δ-Bi2O3) has been studied as a promising electrolyte material for intermediate temperature solid oxide fuel cells (IT-SOFCs) due to its high oxygen ion conductivity in mediate temperature. Especially, the ternary system Bi2O3-Er2O3-WO3 is widely concerned for its high ionic conductivity and thermal stability. In this study, regarding its low melting point, the possibility to deposit dense Bi2O3-Er2O3-WO3 ((Bi2O3)0.705 (Er2O3)0.245 (WO3)0.05, EWSB) electrolyte by plasma spraying was examined. It was confirmed that the sintered EWSB bulk presents a high ion conductivity of 0.34 S cm−1 at 750 °C and excellent stability that indicates no structure transformation and conductivity degradation after annealing at 600 °C for 1000 h. The phase structure and cross-sectional microstructure of plasma-sprayed EWSB were characterized by XRD and SEM. Results showed that the as-plasma-sprayed EWSB presents a dense microstructure with well bonded lamellae. The XRD showed the formation of EWSB with δ-phase and a trace of β-phase, while the β-phase disappeared after annealing at 750 °C for 10 h. The deposited EWSB electrolyte presented the excellent ionic conductivity of 0.26 S cm−1 at 750 °C which can be directly applied to SOFC at intermediate temperature.

Semiconductor ionic based Sm0.2Ce0.8O2−δ-La0.6Sr0.4Fe0.8Cu0.2O3-δ heterostructure for low temperature ceramic fuel cells

Structural design/doping strategy is an efficient method to prepare electrolytes with high oxygen ionic conductivity, but there is still hindrance for solid oxide fuel cell (SOFC) commercialization. Recent advances in semiconductor ionic materials have developed a novel strategy in designing low-temperature electrolyte materials. Here, a heterostructure composite of LSFC (La 0.6 Sr 0.4 Fe 0.8 Cu 0.2 O 3-δ ) and SDC (Sm 0.2 Ce 0.8 O 2−δ ) is developed. The LSFC-SDC composite exhibits a high ionic conductivity, >0.1S/cm at 550 °C. With symmetrical NCAL (Ni 0.8 Co 0.15 Al 0.05 LiO 2-δ )-coated electrode, cells with SDC-LSFC electrolyte exhibit high open-circuit voltage (OCV), and achieve a significant power improvement (>1000 mW/cm 2 ) compared with pure SDC electrolyte at 550 °C. The short-term stability result has proven the operating ability of SDC-LSFC electrolyte under fuel cell environment (H 2 /air). This work demonstrates a new developing route of low-temperature solid oxide fuel cell (LTSOFC), which is different from the conventional SOFC.