Intermediate Temperature Range Research Articles

Perovskite Oxide Catalysts for Enhanced CO2 Reduction: Embroidering Surface Decoration with Ni and Cu Nanoparticles

The imperative reduction of carbon dioxide into valuable fuels stands as a crucial step in the transition towards a more sustainable energy system. Perovskite oxides, with their high compositional and property adjustability, emerge as promising catalysts for this purpose, whether employed independently or as a supporting matrix for other active metals. In this study, an A-site-deficient La0.9FeO3 perovskite underwent surface decoration with Ni, Cu or Ni + Cu via a citric acid-templated wet impregnation method. Following extensive characterization through XRD, N2 physisorption, H2-TPR, SEM-EDX, HAADF STEM-EDX mapping, CO2-TPD and XPS, the prepared powders underwent reduction under diluted H2 to yield metallic nanoparticles (NPs). The prepared catalysts were then evaluated for CO2 reduction in a CO2/H2 = 1/4 mixture. The deposition of Ni or Cu NPs on the perovskite support significantly enhanced the conversion of CO2, achieving a 50% conversion rate at 500 °C, albeit resulting in only CO as the final product. Notably, the catalyst featuring Ni-Cu co-deposition outperformed in the intermediate temperature range, exhibiting high selectivity for CH4 production around 350 °C. For this latter catalyst, a synergistic effect of the metal–support interaction was evidenced by H2-TPR and CO2-TPD experiments as well as a better nanoparticle dispersion. A remarkable stability in a 20 h time-span was also demonstrated for all catalysts, especially the one with Ni-Cu co-deposition.

Enhancing protonic ceramic electrolysis cell performance through electrolyte composition optimization

Polarization resistance, chemical stability against high steam, and faradaic efficiency (FE) are important parameters for steam electrolysis using protonic ceramic electrolysis cells (PCEC) at an intermediate temperature range of approximately 500 °C. To investigate the effects of electrolyte composition on these parameters, PCECs were fabricated using two electrolyte compositions: one without Zr, Ba(Ce0.8Y0.1Yb0.1)O3-δ (BCYYb), and one with Zr, Ba(Ce0.3Zr0.5Y0.1Yb0.1)O3-δ (BCZYYb), as well as a double-layered electrolyte BCYYb/BCZYYb. Although Zr in BCZYYb is required for chemical stability, BCYYb without Zr can also be chemically stable against high steam at 500 °C. Additionally, BCYYb has a higher conductivity compared to BCZYYb, which contributes to lower ohmic resistance and the highest peak power density in H2 fuel at 700 °C (2.04 W/cm2) among the cells with three different electrolytes. However, the BCYYb electrolyte exhibits a slightly higher polarization resistance than BCZYYb. In PCEC operation at 500 °C, the electrolyte composition significantly affects the FE. At a high current density (0.8 A/cm2), the FE of the PCEC with the BCYYb electrolyte (85 %) is significantly larger than that with BCZYYb (68 %).

Tunnel-Structured Phosphate Exhibiting High Proton Conductivity and Thermal Stability over a Wide Intermediate Temperature Range.

For the practical application of fuel cells in vehicles, it is a challenge to develop a proton solid electrolyte that coexhibits thermal stability and high proton conductivity at wide intermediate temperatures. Here, we report on the tunnel structured phosphate KNi1-xH2x(PO3)3·yH2O, which exhibits high proton conductivity at room temperature up to 500 °C, with the conductivity value reaching 1.7 × 10-2 S cm-1 at 275 °C for x = 0.18. This material, composed of the smallest cations that form the tunnel framework with face-shared (KO6) and (NiO6) chains and PO4 tetrahedral chains, retained the rigid framework up to 600 °C. Two oxygen sites of water molecules located adjacent to each other along the PO4 tetrahedral chains in the tunnel provided the proton conduction pathway. The sample maintained a conductivity of 5.0 × 10-3 S cm-1 for 10 h at 150 °C while changing the measurement atmosphere to a N2 gas flow, a 4% H2-96% Ar gas flow, and an O2 gas flow. The conductivity value at x = 0.18 obtained from the DC measurement was in the order of 10-6 S cm-1, close to the instrument's measurement limit. These results demonstrate that tunnel phosphate has potential as a proton solid electrolyte for next-generation fuel cells.

Contribution of strong electron-phonon interaction in the transport properties of La0.8Ca0.2Mn0.5Ni0.5O3 system

La0.8Ca0.2Mn0.5Ni0.5O3 NTC (negative thermal coefficient) thermo-sensitive material was prepared using a conventional solid-state reaction method. From the structural results, we found that the material is pure and crystallizes in the orthorhombic structure with a Pnma space group. It is found that the La0.8Ca0.2Mn0.5Ni0.5O3 ceramic can be used as an NTC thermistor compound in specific temperature sensors and attenuators. Based on Holsten's theory, detailed electrical investigations concerning the nature of the activated small polaron hopping mechanism were reported. The temperature dependence of the DC conductance was used to determine the electrical conduction processes that govern the transport properties of La0.8Ca0.2Mn0.5Ni0.5O3. Hence, the DC mechanisms exhibit changes from the variable range hopping at very low temperatures to the non-adiabatic small polaronic hopping at T = 210 K. In the intermediate temperature range, the semiconductor behavior of La0.8Ca0.2Mn0.5Ni0.5O3 was attributed to the contribution of the tunneling transport process. At various temperatures, the conductance spectra were discussed based on Jonscher and Bruce's laws. Contributions of the overlapping-large-polaron-tunneling, the correlated barrier hopping, the quantum mechanical tunneling, and the non-overlapping small polaron tunneling mechanisms to the transport properties were observed in the dispersive region of the conductance spectra. In addition, Summerfield scaling and corrected Summerfield scaling approaches prove that the charge mobility is temperature-dependent. The positive value of the correction parameter α = 1.2 confirms the presence of interactions in the studied sample.

Localization of overdamped bosonic modes and transport in strange metals

The strange metal phase of correlated electrons materials was described in a recent theory by a model of a Fermi surface coupled a two-dimensional quantum critical bosonic field with a spatially random Yukawa coupling. With the assumption of self-averaging randomness, similar to that in the Sachdev-Ye-Kitaev model, numerous observed properties of a strange metal were obtained for a wide range of intermediate temperatures, including the linear in temperature resistivity. The Harris criterion implies that spatial fluctuations in the local position of the critical point must dominate at lower temperatures. For an [Formula: see text]-component boson with [Formula: see text], we use multiple graphics processing units (GPUs) to compute the real frequency spectrum of the boson propagator in a self-consistent mean-field treatment of the boson self-interactions, but an exact treatment of multiple realizations of the spatial randomness from the random boson mass. We find that Landau damping from the fermions leads to the emergence of the physics of the random transverse-field Ising model at low temperatures, as has been proposed by Hoyos, Kotabage, and Vojta. This regime is controlled by localized overdamped eigenmodes of the bosonic scalar field, also has a resistivity which is nearly linear-in-temperature, and extends into a "quantum critical phase" away from the quantum critical point, as observed in several cuprates. For the [Formula: see text] Ising scalar, the mean-field treatment is not applicable, and so we use Hybrid Monte Carlo simulations running on multiple GPUs; we find a rounded transition and localization physics, with strange metal behavior in an extended region around the transition.

PrBaFe2O6-δ-based composites as promising electrode materials for protonic ceramic electrochemical cells

PrBaFe2O6–δ (PBF) is considered as a promising material for mixed ionic-electronic conductors used in high-temperature applications. In the present work, PBF was used as a basis for two chemical modification approaches, including doping with cobalt, nickel and copper, as well as composite design with the addition of a BaCe0.8Sm0.2O3–δ phase. The single-phase and composite materials were successfully prepared and characterized in terms of their functional properties. The two approaches were found to synergistically affect the functional properties of PBF, allowing a trade-off between thermomechanical and transport properties to be achieved. As a result, the prepared 70 wt% PrBaFe1.9M0.1O6–δ (M = Co, Ni, Cu) + 30 wt% BaCe0.8Sm0.2O3–δ composites exhibit acceptable electrochemical activity in the intermediate-temperature range. The best electrochemical activity was found for the sample with M = Cu, whose polarization resistance at 700 °C reaches 1.7 Ω cm2. Therefore, the designed PBF-based composites can be considered as promising electrode materials for solid oxide fuel cell applications.

Investigation of structural, morphological, and ionic conduction behaviour of Na+ substituted trimeric strontium silicate Sr3–3xNa3xSi3O9-δ (0.00 ≤ x ≤ 0.20)

Extensive research has been carried out to search new electrolytes for Solid Oxide Fuel Cells (SOFCs) in order to reduce their operating temperature in the intermediate temperature range (500 ̊C < t < 800 ̊C) for wide commercialization. Recently, alkali doped strontium silicates materials have been reported to show adequate ionic conductivity in the intermediate temperature range. Hence, in the present work, we have tried to synthesize trimeric Sr3–3xNa3xSi3O9-δ (0.00 ≤ x ≤ 0.20; SNS) system and did a comprehensive study on this system to examine its applicability as a solid electrolyte for electrochemical devices such as IT-SOFCs. The SNS system was prepared via solid state reaction route and characterized by means of XRD, FT-IR and Raman spectroscopy to authenticate the structural phase formation and to gather its spectroscopic traits. The optical Energy band gap of the system was calculated by means of UV-Visible absorption spectroscopy. Surface morphology, microstructure and elemental confinement of the system was examined via Scanning Electron Microscopy (SEM) and Energy dispersive spectroscopy (EDX) techniques. The ionic transport study of the system has been conducted via AC conductivity analysis and Electrical Impedance Spectroscopy (EIS) technique. The highest total conductivity ∼ 0.46×10−2 Scm−1 at 650 ºC was found for the composition Sr2.40Na0.60Si3O9-δ thru EIS method.

Electrochemical performance of Pr0.6Sr0.4Fe0.8Co0.2O3−δ as potential cathode material for IT-SOFC

Solid oxide fuel cells (SOFCs) are renowned for being effective energy sources that have potential to influence how energy is developed in future. SOFCs operate at low temperatures provides different benefits for widespread commercialization. In the present study a perovskite material Pr0.6Sr0.4Fe0.8Co0.2O3−δ (PSFCo) was investigated as cathode for SOFC in intermediate temperature range. Glycine nitrate process was used for the preparation of the samples. PSFCo exhibited cubic structure having small particle size (100–200 nm). The electrical conductivity of the PSFCo was measured as function of temperature up to 850 ℃. The sample displayed maximum electrical conductivity of 370 Scm−1 at around 550–600 ℃. The polarization behavior of PSFCo was calculated by means of AC impedance with Sm0.8Ce0.2O2 (SDC) as electrolyte. The value of area specific resistance (ASR) was calculated as 0.146 Ωcm2 at 800 ℃ and 0.248 Ωcm2 at 700 ℃.

Elaboration of La (Sr/Na) Mn (Ti) O3 ceramic, structural, and morphological investigations, and contribution of direct and indirect interactions on transport properties

The charge carrier's dynamics of La0.7(Sr5/6Na1/6)0.3Mn0.7Ti0.3O3 (LSNMTO) ceramic is conducted using the temperature and frequency dependences of the electrical conductivity and their scaling formalisms. The structural study indicates that LSNMTO crystallizes in a rhombohedral R3‾c perovskite structure with no detectible secondary phases. A phase transition from the high-temperature metallic behavior to the low-temperature semiconductor nature is observed from the electrical conductivity curve at TS-M = 415 K. Further, it is observed that the cation-anion-cation and the cation-cation interactions are present in the material, and play important role in governing the electrical behaviors of LSNMTO. From 200 K to 415 K, the Non-adiabatic Small Polaron Hopping is the predominant conduction process, although the Mott-Variable Range Hopping mechanism governs the conductivity at low temperatures. In the intermediate temperature range, the dynamic of the charge carriers is explained using the Shklovskii Efros model. The frequency-activated conductivity obeyed the universal laws (double-Jonscher and Jonscher laws). At high frequencies, the dispersion of the conductivity spectra is attributed to the presence of hopping and tunneling conduction processes. The Time-Temperature Superposition Principle (TTSP) is obeyed over a large temperature range from 160 K to 350 K. Below 160 K, the deviation from the TTSP is attributed to the coexistence of hopping and tunneling conduction mechanisms. Deviations from the Summerfield scaling and shifts of the isotherms to higher values on decreasing the temperature are due to the local structural disorder in LSNMTO. Therefore, the structural particularities of LSNMTO can result in diverse conduction pathways giving an increase to the deviations from the Summerfield scaling. The studied ceramic exhibits a very motivating maximum negative temperature coefficient of resistance NTCR = −13.36% which is significantly elevated as compared to previously investigated compounds.

Evaluation of Hydrogen Crossover in Pemfcs at Intermediate Temperature (80 - 120 °C)

Proton Exchange Membrane Fuel Cells (PEMFCs) are promising for heavy-duty vehicles (HDV) in the strive to make the transportation sector more sustainable. However, because of the small temperature gradient between the cell (typically run around 80°C) and the ambient temperature, these cells require a large cooling system. Raising the operating temperature to an intermediate temperature range (IT: 80 – 120 °C) would reduce the cooling system size required in HDVs and improve the tolerance towards contaminants, although higher temperature may accelerate degradation [1,2]. To be able to withstand IT operation, reinforcements and chemical modifications have been implemented in commercial PFSA polymers. Unfortunately, most of the data available for PEMFCs are referred to non-reinforced membranes and only few studies analysed the latter under realistic operating conditions. Among some possible issues regarding proton exchange membranes (PEMs), hydrogen crossover is an undesirable, but inevitable phenomenon. The membrane is not perfectly impermeable to hydrogen gas and this results in a safety concern, lower cell efficiency and can lead to faster cell degradation.This work investigates the influence of the reinforcement in a PEM on the hydrogen crossover. Specifically, Nafion HP (reinforced) and Nafion 211 (non-reinforced) are compared under different operating conditions. The purpose of the reinforcement is to improve thermo-mechanical stability, and its physical properties can differ from the rest of the membrane, which can influence hydrogen crossover.Using electrochemical methods, the hydrogen crossover is measured in-situ in a PEMFC with hydrogen on one side and inert gas on the other side. The measurements have been performed between 80 and 120 °C, at different cell relative humidity (RH) conditions (20-90 %) and multiple levels of pressure for both reinforced and non-reinforced membranes. Particular attention has been paid to the case in which the hydrogen side of the cell is more pressurized than the inert side, as this is most often the case in HDV applications. In such conditions, hydrogen permeation increases considerably as a result of the total pressure gradient over the membrane, although this factor is rarely considered in the literature [3]. By adapting the methodology established in our previous work [4], here the effects of the differential total pressure and hydrogen partial pressures are decoupled through a systematic dilution of the hydrogen gas stream. Special points are measured in which the hydrogen partial pressure is kept equal to the ambient case, while the total pressure on the hydrogen side is increased by adding the inert gas, as shown in Figure 1, plot I.Results show that the presence of a reinforcement affects the amount of hydrogen that crosses through the membrane, as seen in Figure 1. Moreover, among the different conditions tested, higher total pressures, especially on the hydrogen side of the cell, are affecting hydrogen crossover the most, while a more modest change is observed for different RH and cell temperatures.The observation that pressure is the most important factor for hydrogen crossover has noteworthy implications and should have an influence when deciding at which pressure the PEMFC is operated in transportation applications. Minimizing hydrogen crossover, while still ensuring adequate cell performance, should be a priority to improve the overall fuel consumption and the electric power obtained from the fuel cell.Figure 1: Hydrogen crossover due to concentration gradients and, in certain conditions, to a differential total pressure. Three different conditions are used to measure crossover, whose results are reported in the right figure: I) the total pressure on the hydrogen side is increased by diluting with inert gas, while the hydrogen partial pressure is kept constant, the inert side is unvaried; II) the total pressure is increased symmetrically on both sides, the hydrogen side is not diluted; III) the total pressure on the hydrogen side is increased and no dilution is employed.[1] Cullen et al., “New roads and challenges for fuel cells in heavy-duty transportation,” Nat. Energy, 2021, doi:10.1038/s41560-021-00775-z.[2] Akitomo et al., “Investigation of effects of high temperature and pressure on a polymer electrolyte fuel cell with polarization analysis and X-ray imaging of liquid water,” J. Power Sources, 2019, doi:10.1016/j.jpowsour.2019.04.115.[3] Kreitmeier et al., “Investigation of membrane degradation in polymer electrolyte fuel cells using local gas permeation analysis,” J. Power Sources, 2012, doi:10.1016/j.jpowsour.2012.03.071.[4] Butori et al., “The Effect of Oxygen Partial Pressure and Humidification in Proton Exchange Membrane Fuel Cells at Intermediate Temperature,” J. Power Sources, 2023, doi:10.1016/j.jpowsour.2023.232803. Figure 1

Enhanced plasticity in a Zr-rich refractory high-entropy alloy via electron irradiation

Refractory high-entropy alloys (RHEAs) possess remarkable high-temperature mechanical properties and have significant potential for use in nuclear fission reactors. However, the phase stabilities of RHEAs are relatively poor in the intermediate temperature range. The coarsening of the nanoprecipitates weakens the plasticity of RHEAs, which imposes substantial restrictions on their scope of application. In this study, electron irradiation was employed to address the challenges associated with nanoprecipitate coarsening and discontinuous precipitation in Zr35Ti30Nb20Al10Ta5 RHEAs after intermediate-temperature annealing. Electron irradiation caused the B2 nanoprecipitates to dissolve, re-precipitate, and induce the precipitation of omega nanoprecipitates. Compared with the unirradiated Zr35Ti30Nb20Al10Ta5 RHEAs with poor plasticity (fracture before yielding), the elongation of irradiated Zr35Ti30Nb20Al10Ta5 RHEAs reaches up to 10 %. This study provides a unique viewpoint and pioneering methodology to effectively tackle the challenge of inadequate plasticity in RHEAs.

Control of the tribological temperature dependence of hydrogenated amorphous carbon films by doping with W

While numerous strategies have been developed to enhance the high-temperature performance of amorphous carbon films, challenges persist regarding high coefficients of friction and wear rates within the mid-temperature range (200–300 °C). In this study, we developed a series of a-C:H(W) films with varying tungsten concentrations and systematically investigated their wear and friction characteristics using Al2O3 ceramic balls at different temperatures. The results reveal that the a-C:H(W) film (W3) with a WC target current of 0.3 A exhibits friction coefficients of 0.10 and 0.06 at 300 °C and 500 °C, respectively. The addition of hydrogen to the film enables stable lubrication in the intermediate temperature range. The presence of carbide facilitates the formation of a continuous protective layer during friction at 500 °C. Additionally, the inclusion of tungsten trioxide effectively reduces friction during high-temperature lubrication. Overall, this a-C:H(W) film shows promise in addressing the challenges of high-temperature wear in mechanical engineering applications under harsh operating conditions.

Influence of the Holding Thickness and Process in the Microstructure and Mechanical Properties of a Microalloyed 380 MPa Structural Steel

Flat low carbon microalloyed structural steels processed by controlled rolling have excellent mechanical properties, particularly regarding toughness, since austenite is rolled with full recrystallization between rolling passes (roughing stage at high temperatures), and, subsequently, with no recrystallization at all between passes (finishing stage at low temperatures), maximizing nucleation of ferrite grains during austenite transformation after hot rolling. However, rolling must be prompted in an intermediate temperature range where recrystallization of austenite between rolling passes occurs partially, as this can lead to great heterogeneity in the grain size distribution of the product, a potential condition to impairs its low temperature toughness. On the other hand, this holding period that is necessary to avoid rolling within this temperature range can last several minutes, reducing the productivity of the rolling line and, in this way, potentially harming the financial performance of the plant. This work was developed to analyze several proposed rolling conditions for the finishing stage during controlled rolling of 16 mm thick strips of a low C Nb-Ti microalloyed steel strip, 380 MPa structural grade, processed in a Steckel mill, to identify the best condition that provides maximum productivity without affecting the required microstructural, toughness and mechanical characteristics of the final product.

Exploring complex magnetic phase transitions and magnetocaloric effect in the nanocrystalline Nd0.5Ca0.5MnO[formula omitted] compound

In this article, we have investigated the temperature and magnetic field-induced complex magnetic phases and magnetocaloric properties of the nanocrystalline Nd0.5Ca0.5MnO3 (NCMO) compound in detail. The compound exhibits charge-ordered antiferromagnetic (CO-AFM) and charge-orbital-ordered antiferromagnetic (AFM) phases at TCO≃ 225 K and TN= 160 K respectively. At the intermediate temperature range, i.e. TN≤ T ≤ TCO, an unfamiliar magnetic state is present where the orbital ordering of manganese ions sets progressively. Both the short-range and zig-zag ordered ferromagnetic (FM) chains and an AFM phase coexist within this temperature window. The effect of magnetic field and temperature drastically modifies the fragile magnetic ground state and this change is also reflected in the magnetocaloric properties of the studied compound. At the low-temperature region, an inverse magnetocaloric effect (MCE) is noticed due to the kinetically arrested magnetic moments of the AFM phase. However, a conventional MCE is noticed in the high-temperature regime. The anomalous behavior of the MCE in the nanocrystalline NCMO compound is analyzed by considering the effect of the reduction of particle size and the meta-stable nature of the magnetic ground state. In addition, we have paid attention to the hysteretic losses associated with the first-order phase transition (FOPT) in order to estimate the magnetic cooling capacity for the material. These studies carry notable importance for the usefulness of nanocrystalline half-doped manganite compounds not only for basic scientific research purpose, but also having possible practical utilization in the magnetic refrigeration industries.

Medium-entropy oxide (Ce0.25Sm0.25La0.25Gd0.25)2O3-δ as promising electrolyte for low-temperature solid oxide fuel cells

The development of high-performance electrolyte is crucial for low-temperature solid oxide fuel cells (LT-SOFCs). Traditional ceria-based materials such as Gd0.1Ce0.9O2-δ (GDC) are promising electrolytes in intermediate-temperature range but their performance drop rapidly with decreasing temperature. Recent advances proposed a new concept for SOFC materials design in terms of entropy, indicative of enormous potential. Herein, a medium-entropy ceria-based oxide (Ce0.25Sm0.25La0.25Gd0.25)2O3-δ (CSLG25) is developed via entropy engineering and evaluated as potential electrolyte for LT-SOFCs by comparing with low-entropy electrolyte GDC. The effects of configuration entropy on crystal structure, oxygen vacancy, electrochemical performance, and proton transport characteristic of the materials are systematically investigated. It is found the CSLG25 cell device exhibits a remarkable power density of 747 mW cm−2 at 520 °C, along with a superionic conductivity of 0.1534 S cm−1. Further study via XPS and Raman technology reveals that the higher entropy of CSLG25 creates more oxygen vacancies and contributes to fast proton transport, which leads to promising fuel cell performance at 430–520 °C. The CSLG25 cell device also delivers the 55.5 h durability performance at 520 °C. This study thus provides a novel electrolyte material for LT-SOFCs and points out a feasible entropy engineering strategy for developing ionic conductors.

Accurate descriptions of molecule-surface interactions for understanding CO2 capture by MgO-based sorbents in wet conditions

MgO shows promise as a CO2 sorbent material for the intermediate temperature range. Here, a hybrid computation scheme, xDH:GGA that combines the XYG3-type of doubly hybrid (xDH) and the generalized gradient approximation (GGA) functionals, is applied. It aims to provide an accurate description of molecular-surface interactions to reduce calculation uncertainties in exploring CO2 capture mechanisms for MgO-based systems. After validating the accuracy of the hybrid scheme by modeling CO adsorption on both MgO(100) and NaCl(100) surfaces against the experimental results, CO2 capture in wet conditions is examined. The results highlight the importance of competitive adsorption between CO2 and water, which undermines the significance of the conventionally identified active sites on MgO surfaces. In contrast, the intermediate Mg(OH)2 layer emerges as a more viable active phase, whose presence was experimentally observed, where the layered structure of Mg(OH)2 is found to kinetically retard water dissociative adsorption. In addition to surface areas and pore structures, our study emphasizes the pivotal role played by selective CO2 chemical adsorption in the development of effective CO2 sorbent materials.

Improved temperature dependence of rate coefficients for rotational state-to-state transitions in H2O + H2O collisions

Aims. We present an improved database of temperature-dependent rate coefficients for rotational state-to-state transitions in H2O + H2O collisions. The database includes 231 transitions between the lower para-states of H2O and 210 transitions between its lower ortho-states (up to j = 7) and can be employed in cometary and planetary applications up to the temperature of 1000 K. Methods. We developed and applied a new general method that allows the generation of rate coefficients for excitation and quenching processes that automatically satisfy the principle of microscopic reversibility and also helps to cover the range of low collision energies by interpolation of cross sections between the process threshold and the computed data points. Results. We find that in the range of intermediate temperatures, 150 &lt; T &lt; 600 K, our new rate coefficients are in good agreement with those reported earlier, but for higher temperatures, 600 &lt; T &lt; 1000 K, the new revised temperature dependence is recommended. The low temperature range, 5 &lt; T &lt; 150 K, is now covered by the above-mentioned interpolation of cross sections down to the process threshold.

Phase Behavior and Defect Structure of HoBaCo2O6-δ

The differential scanning calorimetry study showed that the double perovskite HoBaCo2O6-δ (HBC), depending on its oxygen content, undergoes three phase transitions in the temperature range 298–773 K. Their origin was tentatively explained using the relevant literature data. For the single-phase tetragonal HBC, the oxygen nonstoichiometry dependences on the oxygen partial pressure were investigated by thermogravimetric and flow reactor methods in the intermediate-temperature range of 573–773 K. The proposed defect structure of HBC was successfully verified using the obtained data on its oxygen nonstoichiometry combined with those reported earlier. As a result, the values of the thermodynamic parameters (∆Hi∘, ∆Si∘) of the defect reactions proceeding in HBC were determined. The defect structure of HBC was shown to be similar to that of YBaCo2O6-δ (YBC) likely due to similar ionic radii of Ho3+ and Y3+.

Perovskite SrCo0.5Fe0.25Cu0.2Nb0.05O3-δ cathode for intermediate-temperature solid oxide fuel cells: Improved working stability and CO2 tolerance

Commercial solid oxide fuel cells (SOFCs) primarily operate in the intermediate temperature range (600 °C–800 °C); hence, developing cathode materials with good stability and excellent catalytic activity in this temperature range is necessary. Herein, we are reporting the performance of SrCo0.5Fe0.5O3−δ (SCF) and SrCo0.5Fe0.25Cu0.2Nb0.05O3−δ (SCFCN) perovskite oxide as cathode materials for solid oxide fuel cells (SOFCs). The SCFCN sample maintains a cubic structure under a CO2 atmosphere. The polarization resistance of the SCFCN cathode on La0.9Sr0.1Ga0.83Mg0.17O3−δ (LSGM) reaches 0.067 Ωcm2 at 700 °C. The charge transfer and oxygen reduction reactions of the SCFCN cathode on the LSGM electrolyte are the main rate-limiting steps at 600 °C–700 °C. The SCFCN cathode maintains good electrochemical stability during a 200-h test with a configuration of SCFCN/LSGM/SCFCN symmetrical cell. Compared with SCF, the doping of Cu and Nb effectively reduces the Rp attenuation of SCFCN from 0.00012 to 0.00005 Ωcm2/h. The output power density of the fuel cell with SCFCN as the cathode on LSGM reaches 1124 mWcm−2 at 800 °C. This indicates that SCFCN can be a potential material for fabricating cathode for intermediate-temperature SOFCs (IT-SOFCs).

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