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A dependence of structural transformation and iron exsolution on chemical environment and reducing conditions is proven for the perovskite La0.6Sr0.4FeO3−δ.

The crystal structure changes and iron exsolution behavior of a series of oxygen-deficient lanthanum strontium ferrite (La0.6Sr0.4FeO3-δ , LSF) samples under various inert and reducing conditions up to a maximum temperature of 873 K have been investigated to understand the role of oxygen and iron deficiencies in both processes. Iron exsolution occurs in reductive environments at higher temperatures, leading to the formation of Fe rods or particles at the surface. Utilizing multiple ex situ and in situ methods (in situ X-ray diffraction (XRD), in situ thermogravimetric analysis (TGA), and scanning X-ray absorption near-edge spectroscopy (XANES)), the thermodynamic and kinetic limitations are accordingly assessed. Prior to the iron exsolution, the perovskite undergoes a nonlinear shift of the diffraction peaks to smaller 2θ angles, which can be attributed to a rhombohedral-to-cubic (R3̄c to Pm3̄m) structural transition. In reducing atmospheres, the cubic structure is stabilized upon cooling to room temperature, whereas the transition is suppressed under oxidizing conditions. This suggests that an accumulation of oxygen vacancies in the lattice stabilize the cubic phase. The exsolution itself is shown to exhibit a diffusion-limited Avrami-like behavior, where the transport of iron to the Fe-depleted surface-near region is the rate-limiting step.

Transition-metal-incorporated cerium oxides with Cu and a small amount of Ru (Cu0.18Ru0.05CeOz) were prepared, and their low-temperature redox performance (<423 K) and catalytic alcohol ammoxidation performance were investigated. Temperature-programmed reduction/oxidation under H2/O2 and in situ X-ray absorption fine structure revealed the reversible redox behavior of the three metals, Cu, Ru, and Ce, in the low-temperature redox processes. The initially reduced Ru species decreased the reduction temperature of Cu oxides and promoted the activation of Ce species. Cu0.18Ru0.05CeOz selectively catalyzed the production of benzonitrile in the ammoxidation of benzyl alcohol. H2-treated Cu0.18Ru0.05CeOz showed a slightly larger initial conversion of benzyl alcohol than O2-treated Cu0.18Ru0.05CeOz, suggesting that the reduced structure of Cu0.18Ru0.05CeOz was active for the ammoxidation. The integration of both Cu and Ru resulted in the efficient promotion of ammoxidation, in which the Ru species were involved in the conversion of benzyl alcohol and Cu species were required for selective production of benzonitrile. [ABSTRACT FROM AUTHOR]

In situ 3D computed tomography imaging with statistical analysis successfully revealed the water accumulation and drainage characteristics in the stacked gas diffusion layers (GDLs) and membrane electrode assembly (MEA) of a polymer electrolyte fuel cell. Efficient water drainage at the interface between the cathode GDL and MEA was confirmed upon supplying oxygen to the cathode. [ABSTRACT FROM AUTHOR]

Dynamic M/P invertible helicity was successfully induced at a SiO2 surface immobilized with a dynamic helical trinuclear cobalt complex, [LCo3(NHMe2)6](OTf)3, using chiral ((R) or (S))-1-phenylethylamine. Solid-state CD spectra and theoretical calculations suggested that the fixation of the M/P helical complex on the surface via coordination interactions was the key factor of the induced chirality at the surface. [ABSTRACT FROM AUTHOR]

A non‐solvated alkyl‐substituted Al(I) anion dimer was synthesized by a reduction of haloalumane precursor using a mechanochemical method. The crystallographic and theoretical analysis revealed its structure and electronic properties. Experimental XPS analysis of the Al(I) anions with reference compounds revealed the lower Al 2p binding energy corresponds to the lower oxidation state of Al species. It should be emphasized that the experimentally obtained XPS binding energies were reproduced by delta SCF calculations and were linearly correlated with NPA charges and 2p orbital energies. [ABSTRACT FROM AUTHOR]

For devices encountering long‐term stability challenges, a precise evaluation of degradation is of paramount importance. However, methods for comprehensively elucidating the degradation mechanisms in devices, particularly those undergoing dynamic chemical and mechanical changes during operation, such as batteries, are limited. Here, a method is presented using operando computed tomography combined with X‐ray absorption near‐edge structure spectroscopy (CT‐XANES) that can directly track the evolution of the 3D distribution of the local capacity loss in battery electrodes during (dis)charge cycles, thereby enabling a five‐dimensional (the 3D spatial coordinates, time, and chemical state) analysis of the degradation. This paper demonstrates that the method can quantify the spatiotemporal dynamics of the local capacity degradation within an electrode during cycling, which has been truncated by existing bulk techniques, and correlate it with the overall electrode performance degradation. Furthermore, the method demonstrates its capability to uncover the correlation among observed local capacity degradation within electrodes, reaction history during past (dis)charge cycles, and electrode microstructure. The method thus provides critical insights into the identification of degradation factors that are not available through existing methods, and therefore, will contribute to the development of batteries with long‐term stability. [ABSTRACT FROM AUTHOR]

Iron oxides with various compositions and polymorphs have been widely used as compounds that require reversible redox properties, such as catalysts. However, partial decomposition during phase transitions often causes irreversible degradation of the redox properties of iron oxides. Cr doping into the crystalline framework of iron oxide dendrites improves the stability of the structural transformation of iron oxides. We spatially visualized the FeOx-dendrite phase distribution during oxidation in crystalline dendritic FeOx and Cr-FeOx particles by full-field nano-X-ray absorption fine structure spectroimaging. The spectroimaging visualized propagation in the phase transitions in the individual FeOx particles and changes in the phase transition behaviors of the Cr-FeOx particles. The statistical analysis of the spectroimaging data revealed the phase transition trends in parts of the FeOx and Cr-FeOx particles in three Fe density zones (particle thicknesses) and the probability densities of the phase proportions in the dendrites. [ABSTRACT FROM AUTHOR]