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The single‐atom Fe−N−C catalyst has shown great promise for the oxygen reduction reaction (ORR), yet the intrinsic activity is not satisfactory. There is a pressing need to gain a deeper understanding of the charge configuration of the Fe−N−C catalyst and to develop rational modulation strategies. Herein, we have prepared a single‐atom Fe catalyst with the co‐coordination of N and O (denoted as Fe−N/O−C) and adjacent defect, proposing a strategy to optimize the d‐orbital spin‐electron filling of Fe sites by fine‐tuning the first coordination shell. The Fe−N/O−C exhibits significantly better ORR activity compared to its Fe−N−C counterpart and commercial Pt/C, with a much more positive half‐wave potential (0.927 V) and higher kinetic current density. Moreover, using the Fe−N/O−C catalyst, the Zn‐air battery and proton exchange membrane fuel cell achieve peak power densities of up to 490 and 1179 mW cm−2, respectively. Theoretical studies and in situ electrochemical Raman spectroscopy reveal that Fe−N/O−C undergoes charge redistribution and negative shifting of the d‐band center compared to Fe−N−C, thus optimizing the adsorption free energy of ORR intermediates. This work demonstrates the feasibility of introducing an asymmetric first coordination shell for single‐atom catalysts and provides a new optimization direction for their practical application. [ABSTRACT FROM AUTHOR]

The structure and properties of Mn‐doped 0.67BiFeO3‐0.33BaTiO3 ceramics are systematically investigated with respect to the effects of annealing prior to rapid cooling by quenching in air. Air‐quenching induces a change in crystal structure from pseudo‐cubic to rhombohedral, with higher quenching temperatures leading to an increased rhombohedral distortion. These structural changes are correlated with the appearance of more well‐defined ferroelectric domain configurations. It is shown that the surface preparation procedures for XRD measurements can induce significant changes in the peak profiles, indicating differences in crystal structure between the surface and bulk regions. Frequency dispersion in the temperature‐dependent relative permittivity for the as‐sintered sample is significantly reduced after quenching, accompanied by enhancement of the Curie point and improved temperature‐stability of piezoelectric properties. It is proposed that the formation of defect clusters by A‐site cation diffusion during cooling is circumvented by quenching, leading to the observed modification of structural distortion and ferroelectric properties. [ABSTRACT FROM AUTHOR]

The structures and functional properties of Na0.5Bi0.5TiO3- xKNbO3 (NBT-xKN) solid solutions, with x in the range from 0.01 to 0.09, were investigated using a combination of high-resolution synchrotron X-ray powder diffraction (SXPD) and ferroelectric property measurements. For low KN contents, an irreversible transformation from cubic to rhombohedral phases was observed after the application of a high electric field, indicating that the polar nanoregions (PNRs) in the unpoled state can be transformed into metastable long-range ordered ferroelectric domains in the poled state. In contrast, the near-cubic phase of the unpoled ceramics was found to be remarkably stable and was retained on cooling to a temperature of −175°C. Upon heating, the field-induced metastable ferroelectric rhombohedral phase transformed back to the nanopolar cubic state at the structural transformation temperature, TST, which was determined as approximately 225°C and 125°C for KN contents of 3% and 5% respectively. For the field-induced rhombohedral phase in the poled specimens, the pseudo-cubic lattice parameter, ap, exhibited an anomalous reduction while the inter-axial angle increased towards a value of 90° on heating, resulting in an overall increase in volume. The observed structural changes were correlated with the results of temperature-dependent dielectric, ferroelectric and depolarization measurements, enabling the construction of a phase diagram to define the stable regions of the different ferroelectric phases as a function of composition and temperature. [ABSTRACT FROM AUTHOR]

Aerosol deposition is a feasible method of fabricating dense ceramic films at room temperature by the impact consolidation of submicron‐sized particles on ceramic, metal, glass, and polymer substrates at a rapid rate. Despite the potential usefulness of the aerosol deposition process, there are issues, such as deposition mechanisms and structure of the film‐substrate interface, that are not well understood. We have used complementary structural and microstructural analysis to capture the state of the substrate surface after the aerosol deposition process. The results reveal that modification of the substrate surface by the ejected submicron‐sized particles is essential for the formation of anchoring layer, thereby, a change in internal residual stress state and surface free energy of the substrate is required to deposit film using AD process. Our analysis also suggests that the adhesion between the metal substrate and ceramic particles is possibly contributed by both physical bonding and mechanical interlocking. [ABSTRACT FROM AUTHOR]

2D MXenes have attracted wide attention due to their unique chemical and physical properties. However, MXene nanosheets suffer from restacking and are susceptible to oxidation and consequently lose their functional properties which limits their applications. Thus, it is desirable to explore strategies to preserve MXene nanosheets and avoid oxidation. Herein, an effective strategy to produce MXene‐based conjugated microporous polymers (M‐CMPs) by covalently sandwiching MXene between CMPs using p‐iodophenyl functionalized MXene as templates is demonstrated. The as‐prepared M‐CMPs inherit the 2D architecture and high conductivity of MXene in terms of hierarchical porous structure and large specific surface area of CMPs. Moreover, the restacking and oxidation of MXene are simultaneously suppressed. Such advanced structural merits are critical for electrochemical energy storage. As‐proof‐of‐concept, the M‐CMPs are used as electrode materials for supercapacitors. As expected, with the improved structural advantages, M‐CMPs showcase superior capacitive performance than the MXene and CMPs counterparts. This work not only provides an opportunity for fabricating high performance MXene nanocomposites for energy storage/conversion but also has the potential to be generalized to resolve the challenges in the area of MXene engineering. [ABSTRACT FROM AUTHOR]

This paper herein studies subcritical crack growth ( SCG) behavior of a perovskite-structured Ba0.5Sr0.5Co0.8Fe0.2O3−δ ( BSCF) as an oxygen transport membrane material. The SCG behavior of BSCF is evaluated by a constant load method and constant stress rate method at room temperature ( RT) and 800°C in air, respectively. The low crack velocity measurements are carried out by ring-on-ring bending tests while the high crack velocity measurements by compact tension tests. The stress rates vary approximately from 0.1012 to 101.2 MPa/min. The fracture stress increases with increasing stress rate at 800°C. The SCG parameter, n, of BSCF is determined to be 24.32 and 13.83 at RT and 800°C in air, respectively. This indicates that BSCF is more susceptible to SCG at 800°C. The strength-probability-time ( SPT) diagram is constructed for design proposes. The stress for a lifetime of 40 years should not exceed 27.21 MPa at RT or 4.53 MPa at 800°C to assure a failure probability below 1%. [ABSTRACT FROM AUTHOR]