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Abstract: We report the technical design, implementation and operation of a newly developed X-ray emission spectrometer on the I20 beamline at Diamond Light Source. The spectrometer consists of 14 crystal analysers arranged in an up–down configuration, allowing for operation in one- or two-colour acquisition modes. Since beginning operations in 2023, the spectrometer has substantially enhanced the capability of the beamline to perform X-ray emission spectroscopy (XES) and has demonstrated high reliability with minimal operational issues during user experiments. The latter achievement is particularly significant given the complexity of the instrument, and the difficulty of maintaining the Rowland condition when scanning the energy. We show that the spectrometer can effectively measure spectra in two-colour mode and is capable of detecting weak valence-to-core emission features with a significantly improved signal-to-background ratio. We also present data taken using a newly developed quick-scanning XES acquisition mode, which enables data collection in seconds rather than minutes. This mode opens up possibilities for time-resolved studies and investigating radiation-sensitive materials.

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Abstract: Understanding the interplay between redox behavior and structural stability is crucial for the development of transition metal oxides in electrocatalysis. In this work, we use both X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) to investigate the electrochemical response of Mn-based perovskite oxides (La1–xCaxMnO3) under oxygen reduction reaction (ORR) conditions. This dual approach enables tracking of changes in both the oxidation state and local coordination environment. Mn Kβ XES data show that oxidation-state changes are reversible, despite a shift in transition potentials across a range of compositions, including CaMnO3. In contrast, Mn K-edge EXAFS analyses reveal that while LaMnO3 retains structural integrity, CaMnO3 undergoes irreversible structural changes at low potentials, associated with the collapse of the perovskite framework. Intermediate compositions show partially reversible structural behavior. This decoupling of redox reversibility and structural instability, a picture only accessible through the use of XAS and XES, provides critical insight into the complex behavior of these materials under operational conditions. Additionally, our analysis shows that Mn(II) formation is only detected in CaMnO3 at potentials more negative than 0.4 V (vs RHE). The ORR onset is associated with Mn(IV) reduction, while peroxide formation correlates with an increased Mn(III)/Mn(IV) ratio, supporting a 2e– + 2e– reduction pathway. This study demonstrates the power of XAS and XES analyses to disentangle electronic and structural dynamics, providing a more complete understanding of activity–stability relationships in perovskite electrocatalysts.

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Abstract: Metals play an essential role in cellular homeostasis and are key components of several formulations currently used in the clinic. Synchrotron-based X-ray microscopy at submicron resolution is a powerful approach to map intracellular elemental distributions and to monitor how these patterns change upon genetic or pharmacological perturbations. However, existing sample-preparation protocols often rely on costly and highly specialized equipment for vitrification and dehydration, limiting their widespread adoption. Here, we present an adapted plunge-freezing and freeze-drying workflow that enables the preparation of mammalian cell samples for X-ray fluorescence (XRF) and X-ray absorption spectroscopy (XAS) studies with submicron resolution in a cost-effective and versatile manner. Furthermore, we define acquisition parameters optimized for the reliable detection of low-abundance metals, such as endogenous iron. We anticipate that this accessible protocol will facilitate the broader implementation of synchrotron-based inner-shell spectromicroscopy in cell biology.

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Abstract: Deep-sea sediments hold large quantities of critical rare earth-elements and yttrium (REY) sequestered in nanoparticulate biogenic fluorapatite (Ca5(CO3)x(PO4)3−xF1+x). Understanding their enrichment processes and improving recovery and mineral processing methods require atomic-scale information about their chemical form, but it is difficult to obtain. Here, we use novel high-energy-resolution fluorescence-detected extended X-ray absorption fine structure (HERFD-EXAFS) spectroscopy to elucidate the local structure of gadolinium (Gd) in the highly enriched REY deposit from the Clarion–Clipperton fracture zone (CCFZ) in the Pacific Ocean. Our findings reveal that Gd is neither incorporated into the apatite structure nor precipitated alongside Ce in a Ce–PO4 precipitate. Instead, it is bound at short-range distances to Ca and PO4 in a defective apatite-type bonding environment within an amorphous matrix that encases fluorapatite nanocrystals. Density functional theory (DFT) suggests that Gd and Y, whose atomic fraction is ten times higher than that of Gd, are not dispersed throughout the amorphous matrix, but are likely segregated at medium-range distances. The entrapment of Ce, Gd, and Y within an amorphous matrix explains, at the microscopic level, why REY can be easily recovered through straightforward acid leaching. This is due to the intrinsic instability of disordered atomic structures compared to crystalline phases. This research highlights the complementarity of HERFD-EXAFS and DFT calculations for atomic-scale analysis of trace elements in complex natural matrices. It establishes a basis for their use across diverse terrestrial and marine materials.

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Abstract: Carbon monoxide is one of the most hazardous pollutants in automotive gas exhaust emissions due to its severe impact on the human body and environment. There are many methods for CO removal, including adsorption, methanation, and catalytic oxidation. Catalyst oxidation has been considered the most efficient technique for CO removal. Although CO oxidation has received extensive attention in past decades, achieving high activity and stability at both engine working and cold starting temperatures is still challenging. Noble metal catalysts generally exhibit excellent catalytic activity in high-temperature regions. However, it still suffers from several obstacles, such as over-absorption of CO in low-temperature regions for Pt-based catalysts. Therefore, researchers still focus on seeking alternative candidates for noble metals due to their high cost and low availability, promising non-noble metals including manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu) receive increasing attention due to their high catalytic activity and stability. Many forms of catalysts have been studied exclusively, such as metal catalysts, metal oxide catalysts, supported catalysts, zeolite, and carbon-based catalysts. Supported catalysts with available metal surface area and unique metal-support interfacial perimeter play pivotal roles in heterogeneous catalysis across various industrial applications. Depending on the size of supported active metal, supported metal catalysts can be categorized into particle, cluster, and single-atom catalysts. Among these, single-atom catalysts (SACs) with relatively specific active structures offer prominent advantages in optimizing catalytic activity and product selectivity, leading to an increasing interest in this research area. In recent years, the catalytic performance of SACs has been largely improved through some reported methods including adjusting coordination number, doping heterogeneous atoms, modulating support anchoring sites, and so on. Despite these advancements, it has always been ignored that with the change of the catalyst synthetic process as well as the metal-support interaction (MSI), supported active sites may appear at different positions in catalyst supports, especially at surface or subsurface, thus exhibiting distinct different catalytic behaviour with surrounding molecules. However, the isolated metal site-related location effect is very difficult to deeply explore, because the complexity of catalyst synthesis, combined with the absence of a metal atom location descriptor, poses significant obstacles to achieving precise control over the location of active metal. Herein, we first proposed an electronic metal-support-carbon interaction (EMSCI), which provides a complete picture of the mass and electron flow and expands on the traditional electronic metal-support interactions (EMSI) concept. Furthermore, we reported an exception of EMSI where the interaction between support and metal is not necessary to achieve a high catalytic activity in the CO oxidation reaction, especially in low-temperature regions. The reducibility of CeO2 is investigated by Ce L3 and M4,5 edge NEXAFS, it is confirmed that CeO2 cannot be reduced even under the reductive conditions. Moreover, the location-dependent Cu species have been investigated which are formed during the hydrothermal process using both ex situ and in situ X-ray techniques. The CO oxidation activity shows a positive relation to the percentage of Cu(CO)+ species detected during the reaction. Such behaviour resembles the intrinsic catalytic activity of a true Cu(CO)+ single site, in which the support is completely inactive. This unique phenomenon provides a new scope of understanding metal support interaction and a pathway to optimizing single-atom catalyst performance and catalyst design.