Oxygen Diffusion Research Articles

Rapid oxygen atom capture on perovskite surface boosting the activity and durability of cathode for solid oxide fuel cells

The content and distribution of surface oxygen vacancies are crucial for the oxygen reduction reaction (ORR) activity of solid oxide fuel cell (SOFC) cathodes. Therefore, a facile and rapid oxygen atom capture strategy is developed to modulate the surface oxygen vacancies of the cathode. By controlling the duration of NaBH4 solution reduction, precise modulation of the surface oxygen vacancies of NdBa0.5Sr0.5Co2O5+δ (NBSC) is achieved. Consequently, the processes of oxygen adsorption, dissociation, and diffusion on the surface of the NBSC cathode are enhanced. The research findings demonstrate that NBSC reduced for 10 min (RE-NBSC-10) exhibits optimal ORR catalytic activity and CO2 tolerance. At 800 °C, the Rp of RE-NBSC-10 decreases by 45 %, reaching 0.006 Ω‧cm2. Moreover, the maximum power density (MPD) of the RE-NBSC-10 cathode reaches 1.16 W cm−2, representing a 90.2 % improvement compared to NBSC. This research provides an efficient approach for the advancement of materials tailored for next-generation energy conversion devices.

High extinction risk in large foraminifera during past and future mass extinctions.

There is a strong relationship between metazoan body size and extinction risk. However, the size selectivity and underlying mechanisms in foraminifera, a common marine protozoa, remain controversial. Here, we found that foraminifera exhibit size-dependent extinction selectivity, favoring larger groups (>7.4 log10 cubic micrometer) over smaller ones. Foraminifera showed significant size selectivity in the Guadalupian-Lopingian, Permian-Triassic, and Cretaceous-Paleogene extinctions where the proportion of large genera exceeded 50%. Conversely, in extinctions where the proportion of large genera was <45%, foraminifera displayed no selectivity. As most of these extinctions coincided with oceanic anoxic events, we conducted simulations to assess the effects of ocean deoxygenation on foraminifera. Our results indicate that under suboxic conditions, oxygen fails to diffuse into the cell center of large foraminifera. Consequently, we propose a hypothesis to explain size distribution-related selectivity and Lilliput effect in animals relying on diffusion for oxygen during past and future ocean deoxygenation, i.e., oxygen diffusion distance in body.

Lattice Boltzmann Model Investigation of Simultaneous Imbibition/Evaporation in PEMFC Cathodic Catalyst Layer Using Reconstructed 3D Image Data from Transmission Electron Microscopy

Proton Exchange Membrane Fuel Cells (PEMFCs) are widely used and significant attention is directed towards optimizing of the cathode catalyst layer. The critical focus revolves around refining the multi-phase boundary of the electrically conducting carbon support, the ion-conducting ionomer, the catalyst particles as well as the pore space that can be either occupied by oxygen (feedstock) or water (product). Challenges related to mass transport limitations of oxygen towards these multiple-phase boundaries, also denoted as active sites, persist, especially when liquid water increasingly saturates the pore space (Fig. 1). Furthermore, the evaporated water additionally hinders oxygen transport in the gas phase1,2. This study focuses on the investigation of pore-scale transport mechanisms inside of the cathodic catalyst layer, taking into account the counter-current diffusion of oxygen and water vapor in the gas phase as well as the generation of liquid water that increasingly saturates the void space. For this purpose, a multi-phase and multi-component pore scale Lattice Boltzmann model (LBM), coupled to two-phase reaction, was implemented. The LBM is tailored based on previous works3,4, including the localized generation of water at constant current densities, the imbibition of the pore structure with water counter-currently to the diffusion of oxygen, and the simultaneous evaporation of water. An actual 3D cathode catalyst layer from a commercial membrane electrode assembly, reconstructed from transmission electron microscopy (TEM) image data, was employed. It was imaged using a source voltage of 200kV and a current of 2 nA. The scanned sample had an approximate total volume of 500 × 500 × 100 nm3. From this, a 3D domain of 138 × 138 × 58 nm3 was reconstructed for this study. A 2D cross-section of the reconstructed image is exemplarily shown in Fig. 1. The in-silico study of water and oxygen transport through the catalyst layer elaborates the relationship between the rates of water invasion and evaporation in dependence of current density and catalyst layer structure. The critical conditions for water flooding are evaluated for different process conditions. Fig. 1 Schematic representation of the cathode catalyst layer: The ionomer is represented in white; the carbon for electron connectivity is represented in gray; pore space for oxygen and water transport in yellow; the black circles represent the active sites, i.e., Pt-particles located at the multi-phase boundary of ionomer, carbon and oxygen-filled pores; the red circles represent the inactive sites, that have no connection to ion and/or oxygen transport pathways. References A. Suzuki et al., Int. J. Hydrogen Energy, 36, 2221–2229 (2011) https://www.sciencedirect.com/science/article/pii/S0360319910022913.M. El Hannach, M. Prat, and J. Pauchet, Int. J. Hydrogen Energy, 37, 18996–19006 (2012) https://www.sciencedirect.com/science/article/pii/S0360319912022069.S. Bhaskaran et al., Dry. Technol., 40, 735–747 (2022) https://doi.org/10.1080/07373937.2021.1898417.S. Bhaskaran et al., Int. J. Hydrogen Energy, 47, 31551–31565 (2022) https://www.sciencedirect.com/science/article/pii/S0360319922030932. Figure 1

Application of Hipims Coatings to Enhance the Durability and Performance of Structural Components of PEM Electrolyzer Anodes

Porous transport layers (PTL) and bipolar plates (BPP) are structural elements that transport water, gases, electrons as well as heat within the electrolysis cells. On the anode side, the state-of-the-art material for BPP and PTL is titanium due its higher corrosion resistance under the operating conditions of electrolysis (high electrochemical potential, acidic and oxidizing environment) compared to other materials [1]. However, titanium components tend to form an oxide layer that rises the interfacial contact resistance (ICR) and leads to a poor performance since metal oxides are semiconductors or insulators. This issue is usually addressed by applying precious metal coatings, such as platinum or gold. In this work, we present the potential of high power sputtering techniques (HiPIMS) to manufacture ultra-low loading Pt coatings (<20 nm) with good homogeneity and high performance at an industrial scale. The influence of HiPIMS parameters on coating-substrate interface, as well as the coating properties have been evaluated. SEM, AFM and HRTEM microscopy have been used to evaluate the coating thickness and morphology. XRD analysis has been carried out to evaluate the influence of the HiPIMS parameters on the growth mode of Pt coatings, tailoring the coating texture from [200] to [111]. HiPIMS technique also provide enhanced density compared with other coating techniques due to the higher ionization achieved in the plasma [2]. The deposition of denser and defect-free coatings by HiPIMS enables the application of stainless steel components. HiPIMS prevents the formation of columnar structures and reduces oxygen diffusion. In this work, Nb- and Ti-based protective coatings have been deposited by HiPIMS on stainless steel 316L. A comparative between coated Ti Gr2 and SS316L has been set, showing the potential to reduce costs in the next generation of PEMWE structural components.

Impact of Thermochemical Treatments on Electrical Conductivity of Donor-Doped Strontium Titanate Sr(Ln)TiO3 Ceramics.

The remarkable stability, suitable thermomechanical characteristics, and acceptable electrical properties of donor-doped strontium titanates make them attractive materials for fuel electrodes, interconnects, and supports of solid oxide fuel and electrolysis cells (SOFC/SOEC). The present study addresses the impact of processing and thermochemical treatment conditions on the electrical conductivity of SrTiO3-derived ceramics with moderate acceptor-type substitution in a strontium sublattice. A-site-deficient Sr0.85La0.10TiO3-δ and cation-stoichiometric Sr0.85Pr0.15TiO3+δ ceramics with varying microstructures and levels of reduction have been prepared and characterized by XRD, SEM, TGA, and electrical conductivity measurements under reducing conditions. The analysis of the collected data suggested that the reduction process of dense donor-doped SrTiO3 ceramics is limited by sluggish oxygen diffusion in the crystal lattice even at temperatures as high as 1300 °C. A higher degree of reduction and higher electrical conductivity can be obtained for porous structures under similar thermochemical treatment conditions. Metallic-like conductivity in dense reduced Sr0.85La0.10TiO3-δ corresponds to the state quenched from the processing temperature and is proportional to the concentration of Ti3+ in the lattice. Due to poor oxygen diffusivity in the bulk, dense Sr0.85La0.10TiO3-δ ceramics remain redox inactive and maintain a high level of conductivity under reducing conditions at temperatures below 1000 °C. While the behavior and properties of dense reduced Sr0.85Pr0.15TiO3+δ ceramics with a large grain size (10-40 µm) were found to be similar, decreasing grain size down to 1-3 µm results in an increasing role of resistive grain boundaries which, regardless of the degree of reduction, determine the semiconducting behavior and lower total electrical conductivity of fine-grained Sr0.85Pr0.15TiO3+δ ceramics. Oxidized porous Sr0.85Pr0.15TiO3+δ ceramics exhibit faster kinetics of reduction compared to the Sr0.85La0.10TiO3-δ counterpart at temperatures below 1000 °C, whereas equilibration kinetics of porous Sr0.85La0.10TiO3-δ structures can be facilitated by reductive pre-treatments at elevated temperatures.

Influence of the atmosphere on the phosphorescence of a brominated diphenylphosphine oxide-ethyl naphthaleneimide dyad.

The molecular dyad diphenylphosphine-ethyl bromine naphthaleneimide (Br-DPPENI) emits strong fluorescence and phosphorescence. We studied the intensity and lifetime of the phosphorescence of Br-DPPENI embedded in PMMA films in atmospheres of air, He, Ar, N2, and O2 as a function of pressure between vacuum and ambient pressure (1 bar). The experiment was performed in the frequency domain with a two-channel lock-in amplifier, and the data were analyzed with the polar plot or phasor technique. Reversible shortening of the lifetime due to triplet-triplet annihilation was found in the presence of atmospheric or pure oxygen. With small modulation frequencies, an additional slow component of the phosphorescence dynamics is observed, which is ascribed to the diffusion of oxygen into the sample films.

Customizable Hydrogel Coating of ECM-Based Microtissues for Improved Cell Retention and Tissue Integrity.

Overcoming the oxygen diffusion limit of approximately 200 µm remains one of the most significant and intractable challenges to be overcome in tissue engineering. The fabrication of hydrogel microtissues and their assembly into larger structures may provide a solution, though these constructs are not without their own drawbacks; namely, these hydrogels are rapidly degraded in vivo, and cells delivered via microtissues are quickly expelled from the area of action. Here, we report the development of an easily customized protocol for creating a protective, biocompatible hydrogel barrier around microtissues. We show that calcium carbonate nanoparticles embedded within an ECM-based microtissue diffuse outwards and, when then exposed to a solution of alginate, can be used to generate a coated layer around the tissue. We further show that this technique can be fine-tuned by adjusting numerous parameters, granting us full control over the thickness of the hydrogel coating layer. The microtissues' protective hydrogel functioned as hypothesized in both in vitro and in vivo testing by preventing the cells inside the tissue from escaping and protecting the microdroplets against external degradation. This technology may provide microtissues with customized properties for use as sources of regenerative therapies.

A High Capacity Gas Diffusion Electrode for Li-O2 Batteries.

The very high theoretical specific energy of the lithium-air (Li-O2) battery (3500Wh kg-1) compared with other batteries makes it potentially attractive, especially for the electrification of flight. While progress has been made in realizing the Li-air battery, several challenges remain. One such challenge is achieving a high capacity to store charge at the positive electrode at practical current densities, without which Li-air batteries will not outperform lithium-ion. The capacity is limited by the mass transport of O2 throughout the porous carbon positive electrode. Here it is shown that by replacing the binder in the electrode by a polymer with the intrinsic ability to transport O2, it is possible to reach capacities as high as 31 mAh cm-2 at 1mA cm-2 in a 300µm thick electrode. This corresponds to a positive electrode energy density of 2650Wh L-1 and specific energy of 1716Wh kg-1, exceeding significantly Li-ion batteries and previously reported Li-O2 cells. Due to the enhanced oxygen diffusion imparted by the gas diffusion polymer, Li2O2 (the product of O2 reduction on discharge) fills a greater volume fraction of the electrode and is more homogeneously distributed.

3D culture of ovarian follicles in granular and nanofibrillar hydrogels

3D culture of ovarian follicles in hydrogel matrices is an important emerging tool for basic scientific studies as well as clinical applications such as fertility preservation. For optimizing and scaling 3D culture of preantral follicles, there is a need for identifying biomaterial matrices that simplifies and improves the current culture procedures. At present, microencapsulation of follicles in alginate beads is the most commonly used approach. However, this technique involves notable manual handling and is best suited for encapsulation of single or several follicles. As a potential alternative, we here explore the suitability of different particle-based hydrogel matrices, where follicles can easily be introduced in tunable 3D environments, in large numbers. Specifically, we study the growth of secondary murine follicles in microgranular alginate and nanofibrillar cellulose matrices, with and without cell-binding cues, and map follicle growth against the viscoelastic properties of the matrices. We cultured follicles within the particle-based hydrogels for 10 days and continuously monitored their size, survival, and tendency to extrude oocytes. Interestingly, we observed that the diameter of the growing follicles increased significantly in the particle-based matrices, as compared to state-of-the-art alginate micro-encapsulation. On the other hand, the follicles displayed an increased tendency for early oocyte extrusion in the granular matrices, leading to a notable reduction in the number of intact follicles. We propose that this may be caused by impaired diffusion of nutrients and oxygen through thicker matrices, attributable to our experimental setup. Still, our findings suggest that viscoelastic, granular hydrogels represent promising matrices for 3D culture of early-stage ovarian follicles. In particular, these materials may easily be implemented in advanced culturing devices such as micro-perfusion systems.

Oxygen-generating biomaterials for cardiovascular engineering: unveiling future discoveries

Oxygen-generating biomaterials are emerging as a groundbreaking solution for transforming cardiovascular engineering. These biomaterials generate and release oxygen within various biomedical applications, marking a new frontier in healthcare. Most cardiovascular treatments face a significant challenge, ensuring a consistent oxygen supply to nurture engineered tissues or even implanted devices. Traditional methods relying on passive oxygen diffusion often fall short, hindering functional cardiovascular tissue development. Oxygen-generating biomaterials, incorporating agents like calcium peroxide, provide a controlled oxygen source to the surrounding cells. This innovation potentially enhances cell viability, stimulates growth and boosts metabolic activity crucial for tissue health. Applications include repairing cardiac and vascular tissues, disease modeling, drug testing and personalized medicine, promising tailored treatments. Challenges like material toxicity and oxygen release control need consideration. As research progresses, the use of these innovative biomaterials in clinical translation could reshape cardiovascular healthcare, revolutionizing patient outcomes in heart disease treatment.

Quantifying oxygen diffusion during thermal degradation of combustible porous media

Oxygen diffusion controlled combustion occurs when local oxygen transport is slower than the chemistry, commonly found in porous combustible material or combustible material embedded within an inert porous medium. This mode of combustion, such as smouldering, can pose dangerous fire risks and also be harnessed in environmentally beneficial applications. However, the oxygen diffusion limitation is poorly understood in all contexts and persists as a key knowledge gap. Quantitative analysis of oxygen diffusion effects is therefore crucial for understanding the combustion behavior of combustible porous media and developing precise smouldering simulation models. In this paper, a reactive transport model incorporating both oxygen diffusion and chemical consumption was developed. Using coal as the model fuel, the impacts of key parameters on global mass loss during the one-dimensional diffusion combustion of coal samples were simulated and compared with TGA experiments conducted within a range of oxygen concentrations between 3–21%. Using this method, key kinetic and oxygen diffusion parameters were obtained within reasonable ranges by using a genetic algorithm optimization method. With these optimized parameters, the local oxygen distribution profiles in the samples at different inlet oxygen concentrations were simulated. The results indicate that oxygen diffusion can lead to large oxygen concentration differences within the coal samples, exceeding 63% of the inlet oxygen concentration. These oxygen differences can impact the local chemistry throughout the sample, and lead to fundamental errors in analyzing global kinetic analyses, if the transport effects are not considered. Altogether, this study delivers new insights into a potentially rate-limiting phenomenon that is relevant in progressing knowledge on many fire problems and engineering applications.

A new insight into the oxygen reduction reaction of the Ca3Co4O9+δ/CGO composite air electrode

The calcium cobaltite Ca3Co4O9+δ (CCO) is an emerging electrode for Solid Oxide Fuel Cells or Solid Electrolyser Cells. Thanks to a thermal expansion coefficient which is in the same range of magnitude than the commonly used electrolytes, it should lead to improved durability. However, because the material suffers of a lack of oxide ion conductivity, it has to be used in composite with an ionic conductor. Displaying good compatability with ceria, first studies were carried out on composite with Ce0.9Gd0.1O1.95 (CGO). At 700 °C, an optimal Area Specific Resistance of 0.5 Ω cm2 was obtained for a 50/50 wt.% CCO/ CGO, 21 μm thick electrode, with CCO powder prepared by a solid-state route whose synthesis method led to large grains compared to the CGO powder. Here, to increase the density of triple-phase boundaries between the gas and the two materials, a CCO powder with smaller grain size was prepared using a citrate route. For screen printed 50/50 wt.% CCO (citrate)/CGO composite electrode deposited on symmetrical cell with a CGO electrolyte, an ASR of 0.35 Ω cm2 was achieved at 700 °C, under air. To go further in the understanding of the oxygen reduction reaction, the cell was then carefully studied at variable temperatures and under variable oxygen partial pressures, combining calculation of the distribution function of relaxation times (DFRT) and complex nonlinear least squares fitting (CNLS) of impedance spectra. At 700 °C, under air, it was shown that 55 % of the ASR was due to the oxygen molecule dissociation and diffusion of atomic oxygen species at the surface of the electrode materials. It was only 37 % at 600 °C. Experiment carried out under 21 % of oxygen in helium proved that gas diffusion was a limiting step at temperature higher that 650 °C whereas the redox of CCO was limiting at lower temperature. When deposited on a commercial anode supported 2R-Cell™ half cell, the maximum power density was improved by 284 %, reaching 532 mW/cm2 at 700 °C with a 50/50 wt.% CCO (citrate)/CGO composite air electrode against 187 mW/cm2 for a 50/50 wt.% CCO (solid-state)/CGO composite air electrode at the same temperature.

Microstructure, mechanical performance, thermal stability, and oxidation resistance of AlCrN/AlCrBN nano-multilayer coating

This study synthesized three different coatings using multi-arc ion coating technology: AlCrN, AlCrBN monolayer, and AlCrN/AlCrBN nano-multilayer coatings. A comparative investigation was conducted on the microstructure, mechanical performance, thermal stability, and oxidation properties of coatings. The results indicate the AlCrN, AlCrBN, and AlCrN/AlCrBN nano-multilayer coatings consist of face-centered cubic solid solution fcc-(Cr, Al)N phase. AlCrN/AlCrBN nano-multilayer coatings also exhibit better thermal stability and oxidation resistance than AlCrN and AlCrBN monolayer coatings. The AlCrN/AlCrBN nano-multilayer coatings have a dense, protective, Al2O3 layer formed during high-temperature oxidation. During high-temperature oxidation, the AM (amplitude modulation) decomposition of the AlCrN and AlCrBN monolayers in the AlCrN/AlCrBN nanolayers is inhibited by the structure of the multilayer coatings. The formation of dense oxides on the surface prevents the diffusion of Al and Cr atoms to the outside and prevents the diffusion of oxygen from the outside to the inside of the AlCrN/AlCrBN nanolayers.

Structural and morphological modification of the PEO coating on the Ti-25Ta-10Zr-15Nb alloy through heat treatment

This study aims to produce a Plasma Electrolytic Oxidation (PEO) layer on the Ti-25Ta-10Zr-15Nb alloy (TTZN) and analyze the influence of heat treatment at different temperatures without a controlled atmosphere to promote thermal oxidation, and in a vacuum (10−7 Torr), to prevent oxidation. The results showed that the PEO coating was initially amorphous, and heat treatments promoted the formation of crystalline compounds. Raising the heat treatment temperature led to higher surface roughness in all conditions. The heat treatment under vacuum reduced thickness (9 → 4 μm), while the heat treatment in air promoted a thickness increasing (10 → 174 μm) and decreased the wettability (82 → 25°) of the oxide layer. Due to oxygen diffusion, there was an increase in the hardness of the TTZN alloy at the oxide/metal interface after heat treatment in the air (268 → 504 HV, 268 → 845 HV, and 268 → 1011 HV, at 800, 1000, and 1200 °C).

Consistent differences in tissue oxygen levels across 15 insect species reflect a balance between oxygen supply and demand and highlight a hitherto unknown adaptation for extracting sufficient oxygen from water

Animals, including insects, need oxygen for aerobic respiration and eventually asphyxiate without it. Aerobic respiration, however, produces reactive oxygen species (ROS), which contribute to dysfunction and aging. Animals appear to balance risks of asphyxiation and ROS by regulating internal oxygen relatively low and stable, but sufficient levels. How much do levels vary among species, and how does variation depend on environment and life history? We predicted that lower internal oxygen levels occur in insects with either limited access to environmental oxygen (i.e., insects dependent on aquatic respiration, where low internal levels facilitate diffusive oxygen uptake, and reduce asphyxiation risks) or consistently low metabolic rates (i.e., inactive insects, requiring limited internal oxygen stores). Alternatively, we predicted insects with long life-stage durations would have internal oxygen levels > 1 kPa (preventing high ROS levels that are believed to occur under tissue hypoxia). We tested these predictions by measuring partial pressures of oxygen (PO2) in tissues from juvenile and adult stages across 15 species comprising nine insect orders. Tissue PO2 varied greatly (from 0 to 18.8 kPa) and variation across species and life stages was significantly related to differences in habitat, activity level, and life stage duration. Individuals with aquatic respiration sustained remarkably low PO2 (mean = 0.88 kPa) across all species from Ephemeroptera (mayflies), Plecoptera (stoneflies), Trichoptera (caddisflies), and Diptera (true flies), possibly reflecting a widespread, but hitherto unknown, adaptation for extracting sufficient oxygen from water. For Odonata (dragonflies), aquatic juveniles had higher PO2 levels (mean = 6.12 kPa), but these were still lower compared to terrestrial adults (mean = 13.3 kPa). Follow-up tests in juvenile stoneflies showed that tissue PO2 remained low even when exposed to hyperoxia, suggesting that levels were down-regulated. This was further corroborated since levels could be modulated by ambient oxygen levels in dead individuals. In addition, tissue PO2 was positively related to activity levels of insect life stages across all species and was highest in stages with short durations. Combined, our results support the idea that internal PO2 is an evolutionarily labile trait that reflects the balance between oxygen supply and demand within the context of the environment and life-history of an insect.

Effects of Al and refractory alloying elements (W, Ta and Hf) on oxidation kinetics, oxygen dissolution and diffusion in titanium alloys

The effect of aluminium, tungsten, tantalum and hafnium on the oxidation behaviour of titanium was investigated. Model alloys were oxidized in air for 5000 h at 650 °C. All alloying elements decreased oxide growth and oxygen dissolution in the metal; tungsten was the most efficient. The oxygen diffusivity decreased with aluminium. Tungsten enhanced the formation of Ti2N at the oxide/metal interface which decreased oxygen dissolution in the alloys. Experiments in Ar-20%O2, where Ti2N could not form, confirmed the major role of nitrogen on the oxidation resistance of tungsten-containing alloys. The ternary model alloy Ti-10Al-2W outperformed the high-temperature alloy Ti6242S.

High Temperature Intergranular Oxidation of Nickel Based Superalloy Inconel 718

AbstractIntergranular oxidation (IGO) of the Ni-based superalloy Inconel 718 was studied at 650 °C, 700 °C and 900 °C. The oxidized samples were characterized by X-ray diffraction and scanning electron microscopy. For all the studied temperatures, the external scale was mainly composed of Cr2O3, while the oxides along the grain boundaries were rich in Al and, to a minor extent, Ti. This was consistent with thermodynamic computations. The time evolution of the maximum depth of IGO was found to be parabolic with an apparent activation energy of 164 kJ/mol. The results of this study confirm with three temperatures that IGO kinetics can be described using an extension of the Wagner’s theory of internal oxidation, as recently suggested in the literature at 850 °C. According to this description, the mechanisms controlling the IGO kinetics of Inconel 718 are the aluminum diffusion in the alloy matrix and the oxygen diffusion along the interface between the alloy matrix and the oxidized grain boundary.

Cross-Scale Prediction Model of Oxygen Diffusion in Concrete Under Dry Conditions

Cross-Scale Prediction Model of Oxygen Diffusion in Concrete Under Dry Conditions

Ab Initio Investigation of Oxygen Ion Diffusion in the Layered Perovskite System YSr2Cu2FeO7+δ (0 &lt; δ &lt; 1)

Extensive research on transition metal perovskite oxides as electrodes in solid oxide cells (SOC) has highlighted the potential ability of Fe-based perovskite oxides to catalyze oxygen reduction/evolution reactions (ORR/OER). The layered perovskite-type system YSr2Cu2FeO7+δ has been reported to possess attractive electrocatalytic properties. This work applies density functional theory (DFT) calculations to investigate oxygen ion diffusion in the YSr2Cu2FeO7+δ system. For δ = 0.5, it is found that in the most stable configuration, the oxygen vacancies in the FeO1+δ plane are arranged to form Fe ions in tetrahedral, square pyramid, and octahedral coordination. Ab initio molecular dynamics (AIMD) simulations for YSr2Cu2FeO7.5 (δ = 0.5) yield an oxygen ion diffusion coefficient of 1.28 × 10−7 cm2/s at 500 °C (Ea = 0.37 eV). Complementary results for YSr2Cu2FeO7.2 (δ = 0.2) and YSr2Cu2FeO7.75 (δ = 0.75) indicate that the oxygen diffusion occurs in the FeO1+δ plane, and depends on the oxygen vacancies distribution around the Fe centers.

High-temperature oxidation and ablation behavior of (Zr1/3Hf1/3Ti1/3)C ceramic

With the increasing requirements on thermal protection systems of aerospace aircraft, multi-component ultra-high temperature ceramics (MC-UHTCs) are emerging and considered to be candidate materials. In this work, (Zr1/3Hf1/3Ti1/3)C ceramics were prepared by hot pressed sintering, and the behaviors from oxidation to ablation of the ceramics over a wide temperature range was systematically investigated for the first time. The oxidation rate is controlled by oxygen diffusion at initial stage with high activation energy and is slower at lower oxygen partial pressure. The intermediate layer (Zr,Hf,Ti)CxOy, along with the dense oxide layer formed through preferential oxidation, plays a crucial role in hindering oxygen diffusion. Diffusion of Zr, Hf, and Ti elements during oxidation results in Ti enrichment on the ablation surface, enhancing ablation protection. However, high temperatures and prolonged ablation times cause Ti-rich oxides dissipation and significant evaporation of TiO, resulting a porous surface, compromising ablation protection efficacy.