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The development of cost-effective, non-noble metal electrocatalysts for the oxygen evolution reaction (OER) is of paramount importance for sustainable technologies. Efficient screening strategies for electrocatalysts can greatly increase the commercialization speed of these advanced technologies. Here, ternary phase diagrams with large-scale tuning and designated-scale tuning strategies are applied for the first time to provide a new method for screening perovskite oxide-based electrocatalysts for OERs. Specifically, the family of double perovskites (SrFeCoNiMoO, 0 ≤ x, y ≤ 1.5) was utilized to understand the role of transition metals in perovskite oxides. Ternary phase diagrams can facilitate a rapid screening process, provide a straightforward relationship between phase structures and catalytic activities, and help to confirm the effects of various combinations of transition metals on the OER activity. The Fe-Co system (SrFeCoMoO) improves the catalytic activities, as demonstrated by the reduced Tafel slope and enhanced stability, while the Fe-Ni system (SrFeNiMoO) improves the surface kinetic properties of the OER, as demonstrated by its reduced overpotential. Significantly, the Co, Ni, and Fe ternary phase systems can serve as the synergistic coactive sites (SrFeCoNiMoO) to catalyze the OER, resulting in an improved overall OER performance. This systematic study not only demonstrates a new strategy to allow the rapid screening of double perovskite OER catalysts based on large-scale tuning and designated-scale tuning strategies but, more importantly, also provides an insightful understanding of the use of multitransition metal-based double perovskites for catalysis of the OER.

Y2CoRuO6 was synthesized as a B-site ordered double perovskite with distorted monoclinic P21/n symmetry and an average tilting of the CoO6 and RuO6 octahedra of ψ = 19.7°. DC magnetization measure...

Red-light phosphor materials are crucial components in solid-state lighting (SSL) for simulating natural sunlight. Mn-doped Mg2TiO4 is a promising fluoride-free red-emitting phosphor; however, a sensitizer is necessary to enhance its brightness. In this work, we perform ab initio calculations based on the density functional theory (DFT) to systematically examine the electronic-band coupling between the luminescent center, Mn, and several possible sensitizers, Zn, Nb, Mo, In, Sn, and Ta. Nb was identified as the optimal sensitizer. Well-crystallized 0.1 at. % Mn and 0.0–0.7 at. % Nb-codoped Mg2TiO4 were synthesized at 1450 °C. Synchrotron-radiation-based X-ray absorption spectroscopy (XAS) experimentally validated the proposed atomistic structure, indicating that the Nb5+ dopant substitutes Ti4+ at the 16d sites, leading to the formation of Ti vacancies and of a parasitic MgTiO3 phase. Effective sensitization, resulting in a 243% enhancement of the photoluminescence intensity, was achieved. The 0.1 at. % M...

Novel promising blue MSiAl2O3N2:Ce3+ (M = Sr, Ba) and green BaSiAl2O3N2:Eu2+ oxynitride phosphors with broad band emission for white light-emitting diodes are obtained in this study. The detailed energy transfer mechanism from Ce3+ to Eu2+ in SrSiAl2O3N2 is reported. Moreover, the unexpected red shift emission when the compositional variable x is increased from 0 to 0.92 in the Sr0.92-xBaxSiAl2O3N2:Ce3+0.04,Eu2+0.04 system is well investigated. The decrease in emission energy and the increase in thermal quenching barrier height of x are caused by a dominant chemical pressure compression effect on the activator sites, through which the replacement of Sr2+ (occupied by activators) by larger Ba2+ enhances the covalency of Sr–N/O bonding in spite of unit cell enlargement. The chemical pressure compression effect control for photoluminescence is verified by the ionic-radii equilibrium between 9-coordinate IXSr2+ and (IXCa2+, IXBa2+).

Carbon-supported PdCFe/C catalyst was synthesized by impregnation method. X-ray absorption spectroscopy (XAS) revealed the incorporation of C atoms in PdFe/C clusters and high-temperature annealing was facilitated the formation of the Pd−Fe−C alloy. The catalytic activity oxygen operated via reduction reaction (ORR) of Pd−Fe−C alloy demonstrated the strong dependence upon composition of Pd−Fe−C catalysis, the half-wave potential raise with the increase of iron content. A cyclic voltammetry (CV) test conducted in methanol/ perchloric acid mixed solution was employed to elucidate the tolerance of PdCFe/C electrocatalysts for methanol, which exhibited the methanol-proof character of PdCFe/C electrocatalysts.

Here we demonstrate that the Cu L-edge XANES (X-ray absorption near-edge structure) spectroscopy can be employed for quantitative analysis of the level of carrier-doping in the prototype hole- and electron-doped high-T c superconductor systems, (La 1-x sr x ) 2 CuO 4+δ and (Nd 1-x Ce x ) 2 CuO 4+δ . The progress in hole-doping in the (La 1-x Sr x ) 2 CuO 4+δ system is seen as development of the shoulder peak (due to nominally trivalent copper) on the high-energy side of the main peak (due to nominally divalent copper) in the Cu L 3 -edge region, whereas the progress in electron-doping in the (Nd 1-x Ce x ) 2 CuO 4+δ system results in an additional absorption peak at about 934 eV (due to nominally monovalent copper), together with a decrease in the intensity of the main peak (due to nominally divalent copper). On the basis of these features, Cu-valence values are quantitatively obtained in excellent agreement with those calculated for the same samples from the precise oxygen contents, 4+δ, determined by means of wet-chemical analysis. The valence of Ce in (Nd 1-x Ce x ) 2 CuO 4+δ is revealed to be somewhat lower than +4 (ca. +3.8) on the basis of Ce M 5 -edge XANES data. In the O K-edge XANES spectra, the increase in the CuO 2 -plane hole concentration with increasing x in (La 1-x Sr x ) 2 CuO 4+δ is seen as an enhancement in the intensity of the pre-edge feature at ∼528.9 eV, whereas for (Nd 1-x Ce x ) 2 CuO 4+δ , no signs are observed that could be directly assigned to the change in electron-doping level.

Here we employ both Fe K and L2,3 edge X-ray absorption near-edge structure (XANES) spectroscopy techniques to clarify that in the B-site ordered double-perovskite halfmetal, Sr2FeMoO6.0, iron possesses a mixed-valence state, FeII/III, and accordingly, molybdenum a mixed MoV/VI valence state. A reliable interpretation of the spectral features has been made possible by using a series of samples of the Sr2Fe(Mo,W/Ta)O6.0 system. Replacing MoV/VI gradually with WVI causes an increasing amount of Fe to adopt the FeII state, whereas TaV substitution shifts the valence of iron toward FeIII. As the valence of Fe increases from II to III in the Sr2Fe(Mo,W/Ta)O6.0 system, the absorption energy at the Fe K-edge gradually shifts toward the higher energy side. Similarly, in the L2,3-edge XANES spectra intermediate spectral features are revealed for the Sr2FeMoO6.0 sample in comparison with those for samples heavily substituted with either W or Ta.

The variations of crystal structure, magnetization, and conductivity resulting from the chemical pressure effects of substituting Sr2+ by the smaller Ca2+ in the double-perovskite (Sr2-xCax)FeMoO6 have been investigated. An increase in the Ca content leads to an increase in the Fe/Mo ordering in the materials, which raises the magnetic moments close to the theoretical value of 4 μB. An increase in conductivity with increasing Ca content is also found and is consistent with an increase in (Fe2+ + Mo6+)/(Fe3+ + Mo5+) band overlap rather than bandwidth changes. The changes observed by physical measurements are supported by the X-ray absorption near-edge structures of Fe and Mo and by band structure calculations.

A novel green-yellow emitting Mn2+-doped LiZnPO4 phosphor can be excited under ultraviolet and blue light. The phosphor will be an attractive candidate as an ascendant phosphor for potential applications in light emitting diodes.