Synthesis and Characterization of 40 wt % Ce0.9Pr0.1O2-δ-60 wt % NdxSr1-xFe0.9Cu0.1O3-δ Dual-Phase Membranes for Efficient Oxygen Separation

High-Entropy Perovskites Pr1-xSrx(Cr,Mn,Fe,Co,Ni)O3-δ (x = 0-0.5): Synthesis and Oxygen Permeation Properties

High-entropy perovskite oxides have already been studied in various fields owing to their high-entropy-induced properties. Partial substitution of an element by a lower valence element usually improves the oxygen permeability of perovskite oxides, but high substitution amounts may lead to structural instability. In this work, pure high-entropy perovskites Pr_1-xSr_x(Cr,Mn,Fe,Co,Ni)O_3-δ with high amounts Sr up to x = 0.5 were synthesized via a sol-gel method. Several characterization methods prove that the solubility of Sr increases with higher temperatures of the heating treatment. The ceramic with x = 0.5 shows a transition from semi-conductive to metallic behavior when the temperature reaches 873K. Its oxygen flux is comparable to the low-entropy counterpart La_0.6Sr_0.4Co_0.5Fe_0.5O_3-δ. A stable run of ca. 46.2 h was documented for oxygen permeation under an air/CO₂ gradient.

Zirconium and Yttrium Co-Doped BaCo0.8Zr0.1Y0.1O3-δ: A New Mixed-Conducting Perovskite Oxide-Based Membrane for Efficient and Stable Oxygen Permeation

Oxygen permeation membranes (OPMs) are regarded as promising technology for pure oxygen production. Among various materials for OPMs, perovskite oxides with mixed electron and oxygen-ion (e^-/O^2-) conducting capability have attracted particular interest because of the high O^2- conductivity and structural/compositional flexibility. However, BaCoO_3-δ-based perovskites as one of the most investigated OPMs suffer from low oxygen permeation rate and inferior structural stability in CO₂-containing atmospheres. Herein, zirconium and yttrium co-doped BaCoO_3-δ (BaCo_1-2xZr_xY_xO_3-δ, x = 0, 0.05, 0.1 and 0.15) are designed and developed for efficient and stable OPMs by stabilizing the crystal structure of BaCoO_3-δ. With the increased Zr/Y co-doping content, the crystal structural stability of doped BaCoO_3-δ is much improved although the oxygen permeation flux is slightly reduced. After optimizing the co-doping amount, BaCo_0.8Zr_0.1Y_0.1O_3-δ displays both a high rate and superior durability for oxygen permeation due to the well-balanced grain size, oxygen-ion mobility, crystal structural stability, oxygen vacancy concentration and surface exchange/bulk diffusion capability. Consequently, the BaCo_0.8Zr_0.1Y_0.1O_3-δ membrane delivers a high oxygen permeation rate of 1.3 mL min^-1 cm^-2 and relatively stable operation at 800 ∘C for 100 h. This work presents a promising co-doping strategy to boost the performance of perovskite-based OPMs, which can promote the industrial application of OPM technology.

High-temperature charge transport in Nd0.25Sr0.75FeO3-δ: the influence of various factors

The oxygen content and electrical conductivity in Nd_0.25Sr_0.75FeO_3-δ were measured in the range of oxygen partial pressure from 10^-19 to 0.5 atm at 750-950 °C by coulometric titration and four-probe dc techniques. The thermodynamic analysis of defect equilibrium in the oxide allowed successful simulation of the oxygen content data and calculation of charge carrier concentrations that were used for the analysis of electrical conductivity. The electrical conductivity data were accurately described in the models, which implied that the hole mobility increased upon an increase in the oxygen content in the oxide. The results suggest that only some of the Fe³⁺ sites are available for hole transport, and their fraction increases with an increase in the oxygen content. The migration energy for oxygen ions, electrons and holes was found to be 0.89 ± 0.02, 0.62 ± 0.01 and 0.230 ± 0.006 eV, respectively. Nd_0.25Sr_0.75FeO_3-δ was shown to have a considerable oxygen conductivity (0.12 S cm^-1 at 950 °C) and fairly good stability under reducing conditions, which is a good recommendation for using this oxide as a functional material in high-temperature electrochemical applications.