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Confusion has arisen about the Co spin‐state transition under high pressure for multiferroic BiCoO3. The crystal structure analysis indicates a high‐spin (HS) to low‐spin (LS) state transition with increasing pressure, while Co Kβ X‐ray emission spectra present a high‐spin to intermediate‐spin (IS) state transition. Herein, the spin state of Co3+ in BiCoO3 is investigated utilizing soft X‐ray absorption spectroscopy (XAS) at the Co‐L2,3 and O‐K edges at room temperature under ambient pressure. Furthermore, the spin state transition of Co3+ under high pressure is investigated by Co Kβ X‐ray emission spectra. A pure HS‐Co3+ ground state is found in the BiCoO3 sample prepared from the precursor and oxidizer mixed method—and the existence of a small part of LS‐Co3+ in the BiCoO3 sample prepared from the precursor and oxidizer sandwiched method. A complete HS‐Co3+ to LS‐Co3+ transition is observed under high pressure up to 32.3 GPa. The results clarify the debate on the spin‐state transition of BiCoO3 under high pressure and will deepen our understanding of the intrinsic physical properties on it. [ABSTRACT FROM AUTHOR]

The electrochemical reduction of CO2 is a promising route to convert waste products to valuable chemicals. Search for suitable and efficient CO2 reduction electrocatalysts with high C2:C1 selectivity holds great promise. Herein, for the first time we have developed a molten salt oxidized method to modify the morphology and oxidation state of a Cu‐foam catalyst. The catalyst displayed a current density of 30 mA cm−2 (−1.4 V versus reversible hydrogen electrode) and an ethylene/methane ratio of 870. We provide insight into the improved performance of the catalysts by cross section scanning transmission electron microscopy and quasi in situ soft X‐ray spectroscope, which show that copper oxides are surprisingly reconstructed with Cu (I) and Cu (0) on the surface during the reaction. First principle calculations also demonstrate that the partly reduced Cu2O (111) surface has a high reactivity and selectivity for C2+ products. Furthermore, the molten salt treated catalysts could be applied to the direct synthesis of multi‐carbon fuels, including C3‐C4 compounds in high CO2 pressure electrocatalytic reduction. Our results demonstrate that molten salt are both the oxidizing agent and reaction medium, which is a promising approach for synthesis of highly active CO2 electrocatalysts, which may open a new way for industrial application. [ABSTRACT FROM AUTHOR]

The ability to determine the electronic structure of catalysts during electrochemical reactions is highly important for identification of the active sites and the reaction mechanism. Here we successfully applied soft X-ray spectroscopy to follow in operando the valence and spin state of the Co ions in Li2Co2O4 under oxygen evolution reaction (OER) conditions. We have observed that a substantial fraction of the Co ions undergo a voltage-dependent and time-dependent valence state transition from Co3+ to Co4+ accompanied by spontaneous delithiation, whereas the edge-shared Co–O network and spin state of the Co ions remain unchanged. Density functional theory calculations indicate that the highly oxidized Co4+ site, rather than the Co3+ site or the oxygen vacancy site, is mainly responsible for the high OER activity. Determining catalyst electronic structures during electrochemical reactions is crucial to understand mechanisms. Here authors perform in operando soft X-ray spectroscopy on a cobalt oxide catalyst during O2 evolution and observe voltage and time-dependent valence state transitions. [ABSTRACT FROM AUTHOR]

A negative-thermal-expansion-like volume contraction in LaCu 3 Fe 4 O 12-δ was proposed to result from an inter-site charge transfer between Fe and Cu, namely from Cu3+-Fe3+ at room temperature to Cu2+-Fe3.75+ above 393 K (T C , charge-transfer temperature). Although the partial valence transition of the Fe valence state was observed by Mössbauer spectroscopy and the BVS method, there is no direct observation of the electron transfer to the Cu site in this material until now. In this work, we have studied the valence state of Cu ions in LaCu 3 Fe 4 O 12-δ as a function of temperature across T C using soft x-ray absorption spectroscopy at the Cu- L 3 and the O K edges. We indeed observed a sharp decrease in the valence state of Cu across the phase transition temperature T C. Nevertheless, Cu is 2.2 + and 2.7 + at 440 K and 80 K, respectively, indicates an incomplete inter-site charge transfer across T C. The temperature-dependence Cu- L 3 XAS spectra indicate that there is merely partial electron transfer from Fe to Cu. This is different from the proposed charge transfer from Cu3+-Fe3+ to Cu2+-Fe3.75+ since Cu is not pure 3 + at 80 K far below the phase transition temperature (T C = 393 K) and on the other hand not pure 2 + at 440 K far above T C. Image 1 [ABSTRACT FROM AUTHOR]

During the last 20 years, beamline BL08B has been upgraded step by step from a photon beam-position monitor (BPM) to a testing beamline and a single-grating beamline that enables experiments to record X-ray photo-emission spectra (XPS) and X-ray absorption spectra (XAS) for research in solar physics, organic semiconductor materials and spinel oxides, with soft X-ray photon energies in the range 300-1000 eV. Demands for photon energy to extend to the extreme ultraviolet region for applications in nano-fabrication and topological thin films are increasing. The basic spherical-grating monochromator beamline was again upgraded by adding a second grating that delivers photons of energy from 80 to 420 eV. Four end-stations were designed for experiments with XPS, XAS, interstellar photoprocess systems (IPS) and extreme-ultraviolet lithography (EUVL) in the scheduled beam time. The data from these experiments show a large count rate in core levels probed and excellent statistics on background normalization in the L-edge adsorption spectrum. [ABSTRACT FROM AUTHOR]

Next generation high energy density lithium‐ion batteries have aroused great interests worldwide. Herein, in a high‐voltage (5 V‐class) LiNi0.5Mn1.5O4/MCMB (graphitic mesocarbon microbeads) battery system using 1 m lithium difluoro(oxalate)borate/sulfolane, tris(trimethylsilyl) phosphite (TMSP) additive is added to significantly improve room/high temperature cycling performances. The unchanged X‐ray diffraction patterns suggest the bulk crystal structure of cycled MCMB anode and LiNi0.5Mn1.5O4 cathode are well preserved. Moreover, soft X‐ray absorption spectroscopy (XAS) taken from bulk sensitive fluorescence‐yield (FY) mode reveals the unchanged bulk electronic structure of cycled LiNi0.5Mn1.5O4 cathode. Therefore, it is concluded that only interface instability contributes to capacity fading of full‐cells. However, electrode/electrolyte interface and corresponding interfacial reaction processes are always "enigmatic." First, X‐ray photoelectron spectroscopy (XPS) and in situ differential electrochemical mass spectrometry (DEMS) are used to more accurately decipher the TMSP additive action mechanism in MCMB/electrolyte interfacial reaction processes, by identifying the interfacial solid and gas byproducts, respectively. Then, the crucial role of TMSP additive in modifying cathode/electrolyte interface is revealed by XPS and soft XAS taken from surface sensitive total electron yield (TEY) mode. This paper provides valuable perspectives for formulating novel electrolytes, and for more accurately depicting additive action mechanism in "enigmatic" electrode/electrolyte interfacial reaction processes. [ABSTRACT FROM AUTHOR]

Confusion has arisen about the Co spin‐state transition under high pressure for multiferroic BiCoO3. The crystal structure analysis indicates a high‐spin (HS) to low‐spin (LS) state transition with increasing pressure, while Co Kβ X‐ray emission spectra present a high‐spin to intermediate‐spin (IS) state transition. Herein, the spin state of Co3+ in BiCoO3 is investigated utilizing soft X‐ray absorption spectroscopy (XAS) at the Co‐L2,3 and O‐K edges at room temperature under ambient pressure. Furthermore, the spin state transition of Co3+ under high pressure is investigated by Co Kβ X‐ray emission spectra. A pure HS‐Co3+ ground state is found in the BiCoO3 sample prepared from the precursor and oxidizer mixed method—and the existence of a small part of LS‐Co3+ in the BiCoO3 sample prepared from the precursor and oxidizer sandwiched method. A complete HS‐Co3+ to LS‐Co3+ transition is observed under high pressure up to 32.3 GPa. The results clarify the debate on the spin‐state transition of BiCoO3 under high pressure and will deepen our understanding of the intrinsic physical properties on it. [ABSTRACT FROM AUTHOR]

• Mo-doping is responsible for an enhanced OER activity of the exsoluted catalyst Co 0.76 Fe 0.18 Mo 0.06 O 1.35. • Mo-doping enhanced the oxidation state of the exsolved Co 0.76 Fe 0.18 Mo 0.06 O 1.35 before and after OER. • The O-K SXAS spectra revealed no La ions at the surface layers, and confirmed the formation of oxyhydroxide. Developing and understanding efficient catalysts for anodic oxygen evolution reaction (OER) is critical for the electrochemical production of H 2 for energy storage and transformation. Herein, a Co 0.76 Fe 0.18 Mo 0.06 O 1.35 catalyst with a spinel structure (CFMO-800) was prepared from Mo-doped LaCo 0.8 Fe 0.2 O 3 perovskites (LCF) by a simple exsolution method. The CFMO-800 catalyst exhibited a low potential of 1.48 V (vs. RHE) at a current density of 10 mA cm−2 in 1 M KOH surpassing all spinel and perovskite Co/Fe oxide catalysts reported. The surface-sensitive soft X-ray absorption spectroscopies (SXAS) at the Co-L 2,3 and the O-K edges revealed an unexpected increase in the Co valence state of CFMO-800 upon doped with the high-valence Mo and the clear formation of Co/Fe (oxyhydr)oxides on the surface layers of the exsolved catalyst. This study presents a strategy for the surface reconstruction by combining the exsolution and the high-valence ion doping to develop highly active electrochemical catalysts. [ABSTRACT FROM AUTHOR]