The electrochemical conversion of CO2 to CO in membrane electrode assembly (MEA) electrolyzers using gas diffusion electrodes (GDEs) offers a sustainable and scalable pathway for carbon utilization. Here, we present a one-step atomic layer deposition (ALD) approach to prepare ZnO-based GDEs with tunable loadings and high selectivity toward CO. Increasing the number of ALD cycles raises the ZnO loading but progressively reduces the pore accessibility within the GDE. An optimal balance is achieved at 200 ALD cycles, delivering a peak CO faradaic efficiency (FECO) of 88% and a full-cell energy efficiency of 38% at −100 mA cm−2. Crucially, the scalability of ALD is demonstrated through stable long-term testing, achieving 85% FECO in a 5 cm2 MEA after 30 h, and 80% FECO in a 100 cm2 MEA after 24 h. These results establish ALD as an effective and versatile strategy for fabricating high-performance ZnO electrodes for CO2 electrolysis.

We investigated the valence dynamics of thin films during the electrocatalytic oxygen evolution reaction using operando high-energy-resolution fluorescence-detected (HERFD) X-ray absorption spectroscopy (XAS) in a 0.1 M KOH solution under an applied potential. We show that it is possible to measure the 10 unit cell (∼4 nm) bimetallic perovskite oxide La2CoMnO6 thin film grown on Pt-covered SiNx membranes. Operando Co and Mn K-edge HERFD XAS spectra on the active surface species were recorded from the backside of the SiNx membrane. The HERFD XAS Co K-edge spectra reveal a (partial) increase in the oxidation state from Co2+ in ex situ conditions to mainly Co3+ in the solid-liquid open-circuit voltage (OCV). Voltage-dependent Co K-edge HERFD XAS white line intensities show that Co is oxidized toward the higher oxidation state, while Mn remains Mn4+. Interestingly, the Co and Mn main edge shifts with the average valence change of 0.20; the valence of Mn is constant, implying that the valence of Co increases by 0.40. The OCV spectra were reversible when switching off the potentials. These observations clearly identify element-specific valence dynamics in the intrinsic oxygen evolution reaction.

X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS) are powerful probes of electronic structure owing to their chemical and orbital selectivity. For powder samples, however, interpreting RIXS spectral intensities remains challenging as the measured signal is an average over all orientations. Existing theoretical treatments rely largely on spherical-tensor formalisms, which often involve complex derivations and case-specific analyses. Meanwhile, recent advances in quantum-chemistry methods have made the evaluation of transition tensors in Cartesian coordinates both accurate and straightforward. Here, we present a general theoretical framework that translates Cartesian transition tensors into physically meaningful, orientation-averaged intensities for powder samples. The formalism allows predicting angular and polarization dependences ab initio for both XAS and RIXS and is extendable to other spectroscopies. The resulting predictions show excellent agreement with RIXS experimental data at the Ce L_3 edge.

We investigate the electronic structure of AgF_{2}, AgFBF_{4}, AgF, and Ag_{2}O using x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS) at the Ag L_{3} edge. XAS results were compared with density functional theory computations of the spectra, allowing an identification of main features and an assessment of the theoretical approximations. Our RIXS measurements reveal that AgF_{2} exhibits charge-transfer (CT) excitations and dd excitations, analogous to those observed in La_{2}CuO_{4}. We propose to use the ratio of dd to CT spectral weight as a measure of the covalence of the compounds and provide explicit equations for the weights as a function of the scattering geometry for crystals and powders. The measurements at the metal site L_{3} edge and previous measurement in the ligand K edge reveal a striking similarity between the fluoride and cuprate materials, with fluorides somewhat more covalent than cuprates. These findings support the hypothesis that silver fluorides are an excellent platform to mimic the physics of cuprates, providing a promising avenue for exploring high-T_{c} superconductivity and exotic magnetism in quasi-two-dimensional (AgF_{2}) and quasi-one-dimensional (AgFBF_{4}) materials.

Nickel-rich layered oxides, such as LiNi0.8Co0.1Mn0.1O2 (NMC811), are considered as an attractive cathode active material (CAM) due to their high power and high energy density. However, NMC811 CAM faces severe challenges, such as structural instability and high surface reactivity at high voltages. To overcome these challenges, cerium doping by solid-state synthesis route and CeOx coatings by atomic layer deposition (ALD) technique not only stabilize the NMC811 structure but also provide a safe protective layer on the electrode surface. The optimized electrochemical performance achieved by incorporating cerium into the NMC811 structure enhances cycling stability at the voltage range of 3.0 - 4.4 V in Li half-cells, as confirmed by X-ray absorption spectroscopy (XAS), indicating a cerium oxidation state of +4. Likewise, CeOx coatings (similar to 1 nm) by ALD technique enhances the rate performance and cycling stability at high voltages (3.0 - 4.6 V) in Li half cells due to the formation of Ce3+ on the surface of NMC811 electrodes, confirmed by XAS analysis. Overall, doping and coating demonstrate that cerium is effective in both strategies, especially the ALD technique helps to reduce metal dissolution, better cycling stability and achieve high voltage operations. This work highlights the role of cerium incorporated by doping and coatings on the surface in order to stabilize the NMC811 structure and suppress the parasitic reactions that occur at high voltages to utilize the full capacity.

Atomic/molecular layer deposition (ALD/MLD) offers a comprehensive process and application portfolio for metal-organic thin films; however, ALD/MLD process development for transition-metal-based materials remains very limited, despite the versatile functional properties of their compounds. In this work, to enrich the chemistry of transition metal precursors in ALD/MLD, an all-nitrogen-coordinated cobalt complex, Co(tmsaedma)(2) (tmsaedma = Bis(N,N-dimethyl(N'-trimethylsilyl)ethane-1-amino-2-amido), was employed as the metal precursor for the first time. The Co-N coordination provides an optimal reactive site for a variety of organic linker groups, as demonstrated here by three organic precursors that share the same rigid benzene backbone but differ in reactive groups: 1,4-benzenediol (hydroquinone; HQ), 1,4-benzenedithiol (BDT), and 1,4-benzenedicarboxylic acid (terephthalic acid; BDC). A comprehensive set of characterization techniques, combined with first principles density functional theory (DFT) calculations, is used to systematically investigate the three new ALD/MLD processes and the stability of the resulting Co(II)-organic thin films: Co-HQ, Co-BDT, and Co-BDC. The reactivity and stability trends of the organics are found as BDC>HQ>BDT and BDC>>BDT>>HQ, respectively. Decomposition mechanisms are provided for Co-HQ and Co-BDT. Furthermore, the preparation of low-density, porous CoO thin films with tunable structural and optical properties, difficult to achieve otherwise, is demonstrated via calcination in N-2 of the Co-BDC thin films.

Reduced organic sulfur (S) functional groups play critical roles in diverse environmental and biological processes, but an enduring analytical challenge is resolving thiols (R-SH) and thioethers (R-S-R') in complex mixtures. Here, we demonstrate the use of S Kα1 high-energy-resolution fluorescence detected (HERFD) X-ray absorption near-edge structure (XANES) spectroscopy to distinguish thiol groups from thioether moieties in complex environmental mixtures as a function of pH. Experiments with model S thiol compounds showed a quantitative decrease in the normalized amplitude of the reduced S peak in spectra with thiol deprotonation (R-SH ↔ R-S- + H+), a phenomenon not observed for other S functionalities. Spectra were collected across a pH range relevant to thiol pKas (3-11) for five well-characterized dissolved organic matter (DOM) samples from natural environments, containing different S content and various mixtures of S functionalities. Using a quantitative relationship between the decrease in the reduced S peak amplitude and thiol deprotonation in composite spectra of model S compounds, the proportions of reduced S as thiols (fRS-) in the five DOM samples were quantified to range from 3% to 41%. For two DOM samples, we quantified thiol pKa distributions and verified reversibility through stepwise, bidirectional pH adjustments. The increase in thiol abundance of one DOM sample following experimental abiotic sulfurization was also quantified to demonstrate method application. We discuss opportunities to optimize S Kα1 HERFD-XANES spectroscopy for enhanced thiol sensitivity in various research applications.

Heterogeneous catalysts have emerged as a potential key for closing the carbon cycle by converting carbon dioxide (CO 2 ) into value-added chemicals. In this work, we report a highly active and stable ceria (CeO 2 )-based electronically tuned trimetallic catalyst for CO 2 to CO conversion. A unique distribution of electron density between the defective ceria support and the trimetallic nanoparticles (of Ni, Cu, Zn) was established by creating the strong metal support interaction (SMSI) between them. The catalyst showed CO productivity of 49,279 mmol g −1 h −1 at 650 °C. CO selectivity up to 99% and excellent stability (rate remained unchanged even after 100 h) stemmed from the synergistic interactions among Ni-Cu-Zn sites and their SMSI with the defective ceria support. High-energy-resolution fluorescence-detection X-ray absorption spectroscopy (HERFD-XAS) confirmed this SMSI, further corroborated by in situ electron energy loss spectroscopy (EELS) and density functional theory (DFT) simulations. The in situ studies (HERFD-XAS & EELS) indicated the key role of oxygen vacancies of defective CeO 2 during catalysis. The in situ transmission electron microscopy (TEM) imaging under catalytic conditions visualized the movement and growth of active trimetallic sites, which completely stopped once SMSI was established. In situ FTIR (supported by DFT) provided a molecular-level understanding of the formation of various reaction intermediates and their conversion into products, which followed a complex coupling of direct dissociation and redox pathway assisted by hydrogen, simultaneously on different active sites. Thus, sophisticated manipulation of electronic properties of trimetallic sites and defect dynamics significantly enhanced catalytic performance during CO 2 to CO conversion.

We report the valence-to-core resonant inelastic x-ray scattering (RIXS) of EuS measured at the L3 edge of Eu. The obtained data reveal two sets of excitations: one set is composed of a hole in the S 3p bands and an electron excited to extended Eu 5d band states, the other is made up from a hole in the Eu 4f states and an electron in localized Eu 5d states bound to the 4f hole by its Coulomb potential. The delocalized excitations arise from the dipole-allowed 5d to 2p emissions, whereas the localized excitations result from the dipole-forbidden (quadrupole-allowed) 4f to 2p emissions. Both these emission channels have a comparable intensity thanks to a small number of occupied 5d states (approximately 0.6) combined with a large number of occupied 4f states (seven). We identify the localized electron-hole pairs with the "magnetic excitons" suggested in the past as an interpretation of the sharp features seen in the optical absorption spectra. Our observations provide a direct experimental evidence of these excitons which has been missing up to now.

Two-phase synthesis is a well-established approach for achieving precise control of the nanoparticle properties. However, studying and understanding chemical transformations in such a spatially heterogeneous system is challenging. In this work, we introduce a two-phase synthesis route for ZnS nanoparticles (ZnS NPs) at the water-toluene interface. By employing spatially resolved in situ high-energy resolution fluorescence-detected X-ray absorption spectroscopy (HERFD-XAS) combined with density functional theory (DFT) calculations, we track the diffusion of Zn2+ species at the interface, identify key reaction intermediates, and monitor the nucleation and growth of ZnS NPs within the toluene phase. We propose the formation of a [Zn(H2O)6]2+ complex upon dissolving Zn(Ac)2 in water and the diffusion of Zn2+ ions from water to toluene driven by the formation of an octahedral [Zn(OA)6]2+ complex (OA = oleylamine). Furthermore, by complementing HERFD-XAS with total X-ray scattering analysis, we show the formation of an intermediate tetrahedral [Zn(SR)4]2+ complex at 60 °C and its successive transformation to noncrystalline ZnS nuclei at 80 °C and crystalline ZnS NPs starting at 100 °C. Thus, we demonstrate how in situ X-ray spectroscopy can elucidate the coordination and diffusion of Zn2+ ions, and, in combination with X-ray scattering studies, identify the emergence of atomic and electronic structures during the two-phase synthesis of ZnS nanoparticles.

Electrochemically generating hydrogen peroxide (H 2 O 2 ) from oxygen offers a more sustainable and cost‐effective alternative to conventional anthraquinone process. In alkaline conditions, H 2 O 2 is unstable as HO 2 − , and in neutral electrolytes, alkali cation crossover causes system instability. Producing H 2 O 2 in acidic electrolytes ensures enhanced stability and efficiency. However, in acidic conditions, the oxygen reduction reaction mechanism is dominated by the inner‐sphere electron transfer pathway, requiring careful consideration of both reaction and mass transfer kinetics. These stringent requirements limit H 2 O 2 production efficiency, typically below 10–20% at industrial‐relevant current densities (>300 mA cm −2 ). Using a multiscale approach that combines active site tuning with macrostructure tuning, this work presents an octahedron‐like cobalt structure on interconnected hierarchical porous nanofibers, achieving a faradaic efficiency exceeding 80% at 400 mA cm −2 and stable operation for over 120 h at 100 mA cm −2 . At 300 mA cm −2 , the optimized catalyst demonstrates a cell potential of 2.14 V, resulting in an energy efficiency of 26%.

The deployment of proton-exchange-membrane fuel cells is hindered by the large amount of Pt required for anode and cathode electrocatalysis. While Fe–N–C materials have shown promising initial oxygen reduction reaction (ORR) activity, they lack durability. Key degradation mechanisms include direct demetallation of Fe-N 4 sites and indirect deactivation caused by reactive oxygen species. Enhanced durability of Fe–N–C materials can be achieved by interfacing them with a low amount of Pt nanoparticles (NPs) or even Pt single atoms. 1-2 The original idea was to lean on the known activity of bulk Pt and Pt NPs towards H 2 O 2 electroreduction. However, different Pt and Fe active sites can emerge in the current process for preparing Pt/Fe-N-C hybrid materials due to a relatively high-temperature step needed to reduce the Pt salt, leading to the transformation of some Fe-N 4 sites into Pt@FeO x core-shell structures, etc. The presentation will show that it is possible to add controlled amounts of Pt NPs (0.25-2.0 wt. %) via a soft polyol method, resulting in unmodified Fe coordination, well-defined Pt structures and stable Pt/Fe–N–C hybrids. The approach is first validated for various mainstream Fe–N–Cs, including ZIF-8-derived Fe-N-C, aerogel derived Fe-N-C and silica-templated Fe-N-C. With operando techniques, we demonstrate that the Pt addition nearly suppresses H 2 O 2 production during ORR and strongly reduces the Fe leaching rate during ORR, while post mortem Mössbauer spectroscopy reveals that the highly active but unstable Fe(III)N 4 site is partially stabilized. The similar H 2 O 2 electroreduction activity of Pt/Fe–N–C and Fe–N–C and other analyses point toward a long-distance electronic effect of Pt NPs in stabilizing FeN 4 sites. This key stability property of Fe-N 4 sites during ORR brought by a low amount of Pt is experimentally elusive to understand. Possible synergistic effects between Pt and Fe-N 4 sites were further studied with density functional theory and a proposed mechanism will be presented that could explain the experimental observations. Fig. 1 . Characterization of catalysts in PEMFC or in gas diffusion electrode (GDE) setup. a) Chronoamperometry at U = 0.5 V, b) Online ICP-MS results conducted in a GDE setup in O 2 -saturated 0.1 M HClO 4 electrolyte, the Fe dissolution rates of Fe–N–C Aero and Pt/Fe–N–C Aero were normalized to catalyst loading during an accelerated stress test (AST) consisting of 200 square cycles of 3.2 s at -49.7 mA·cm -2 and 2.1 s at -0.1 mA·cm -2 . The aerogel-derived Fe-N-C catalyst (Fe-N-C Aero ) has an Fe content of 1.25 wt. %, and 1 wt. % Pt NPs was deposited onto it to form the Pt/Fe-N-C Aero hybrid. References: Mechler, A. K.; Sahraie, N. R.; Armel, V.; Zitolo, A.; Sougrati, M. T.; Schwämmlein, J. N.; Jones, D. J. ; Jaouen, F.; Electrochem. Soc. 2018 , 165, F1084. Bae, G.; Kim, M. M.; Han, M. H.; Cho, J.; Sougrati, M-T.; Kim, J.; Lee, K-S.; Joo, S. H.; Goddard, W. A.; Oh, H-S.; Kim, H.; Jaouen, F.; Choi, C. H.; Nature Catal. 2023 , 6, 1140-1150. Figure 1

Deep-sea mud is rich in rare-earth elements, primarily found in fluorapatite, a mineral deposit that forms over hundreds of thousands to millions of years through the accumulation of fish remains. After fish die, biogenic apatite captures rare earth elements from seawater on the seafloor and from pore waters during the diagenesis process. The conventional model for rare earth element enrichment suggests that they are incorporated into the bioapatite crystal structure through solid-state diffusion. However, our data reveal that cerium atoms are instead precipitated within an amorphous layer surrounding bioapatite nanocrystals, as shown by high-energy-resolution X-ray absorption spectroscopy and transmission electron microscopy. Computational simulations further support this finding, predicting that cerium atoms cluster on the surface of fluorapatite. These results suggest that the fluorapatite-water interface plays a crucial role in the enrichment of cerium, as well as other rare earth elements, in marine sediments.

Promising cathode materials for fluoride-ion batteries (FIBs) are 3d transition metal containing oxides with Ruddlesden-Popper-type structure. So far, multi-elemental compositions were not investigated, but could alternate electrochemical performance similar to what had been found for cathode materials for lithium-ion batteries. Within this study, we investigate RP type La2Ni0.75Co0.25O4.08 as an intercalation-based active cathode material for all-solid-state FIBs. We determine the structural changes of La2Ni0.75Co0.25O4.08 during fluoride intercalation / de-intercalation by ex-situ X-ray diffraction, which showed that F- insertion leads to transformation of the parent phase to three different phases. Changes in Ni and Co oxidation states and coordination environment were examined by X-ray absorption spectroscopy and magnetic measurements in order to understand the complex reaction behaviour of the phases in detail, showing that the two transition metals behave differently in the charging and discharging process. Under optimized operating conditions, a cycle life of 120 cycles at a critical cut-off capacity of 40 mAh g-1 against Pb/PbF2 was obtained, which is one of the highest observed for intercalation electrode materials in FIBs so far. The average Coulombic efficiencies ranged from 85% to 90%. Thus, La2Ni0.75Co0.25O4.08 could be a promising candidate for cycling-stable high-energy cathode materials for all-solid-state FIBs

A two-phase synthesis has been well established for achieving precise control of nanoparticle properties. However, studying and understanding chemical transformation in such a spatially heterogeneous system is challenging. In this work, we introduce a two-phase synthesis route for ZnS nanoparticles (ZnS NPs) at the water-toluene interface. By employing spatially resolved in situ high-energy resolution fluorescence-detected X-ray absorption spectroscopy (HERFD-XAS) combined with density functional theory (DFT) calculations, we track the diffusion of Zn²⁺ species at the interface, identify key reaction intermediates, and monitor the nucleation and growth of ZnS NPs within the toluene phase. We propose the formation of a [Zn(H2O)¬6]2+ complex upon dissolving Zn(Ac)2 in water and the diffusion of Zn2+ ions from water to toluene driven by the formation of an octahedral [Zn(OA)6]2+ complex (OA = oleylamine). Furthermore, by complementing HERFD-XAS with total X-ray scattering analysis, we show the formation of an intermediate tetrahedral [Zn(SR)4]2+ complex at 60 °C and its successive transformation to non-crystalline ZnS nuclei at 80 °C and crystalline ZnS NPs starting at 100 °C. Thus, we demonstrate how in situ X-ray spectroscopy can elucidate the coordination and diffusion of Zn²⁺ ions, and, in combination with X-ray scattering studies, identify the emergence of atomic and electronic structures during the two-phase synthesis of ZnS nanoparticles.

This study explores how the strategic material design introduced synergetic coupling of strong metal-support interaction (SMSI) between copper (Cu) nanoparticles and titanium dioxide (TiO2) loaded on dendritic fibrous nanosilica (DFNS), defects within TiO2, and localized surface plasmon resonance (LSPR) of Cu. Mechanistic insights were gained using in situ high-energy radiation fluorescence detection X-ray absorption near edge structure (HERFD-XANES) spectroscopy, electron microscopy, and finite-difference time-domain (FDTD) simulations. The introduction of copper nanoparticles onto the TiO2 surface induces a change in the electronic structure and surface chemistry of TiO2, due to the electronic interactions between Cu sites and TiO2 at the interface, inducing SMSI. This resulted in enhancing light absorption, efficient charge transfer, reducing electron-hole recombination and enhancing the overall catalytic efficiency. The activation energy for CO2 reduction was significantly reduced in light as compared to dark. Control experiments revealed a dominant role of photoexcited hot carriers, alongside photothermal effects, in driving CO2 reduction, supported by super-linear light intensity dependence and reduced activation energies. The unique interplay of O-vacancy defects, electron-hole separation in TiO2 and LSPR effects in Cu led to the excellent performance of the DFNS/TiO2-Cu10 catalyst. The catalyst outperformed the reported photocatalytic systems with a CO production rate of ∼3600 mmol gCu -1 h-1 (360 mmol gcat -1 h-1) with nearly 100% selectivity. A reaction mechanism was proposed based on the intermediates observed using the in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and co-related to the electron transfer pathways to different reactants using HERFD-XANES. The study concluded that the synergistic coupling of Cu LSPR, charge carrier separation via SMSI at the Cu-TiO2 interface, and O-vacancy defects stabilized by SMSI enhance the photocatalytic CO2 reduction performance of this hybrid system.

While Fe-N-C materials have shown promising initial oxygen reduction reaction (ORR) activity, they lack durability in acidic medium. Key degradation mechanisms include FeN4 site demetallation and deactivation by reactive oxygen species. Here we show for mainstream Fe-N-Cs that adding 1 wt.% Pt nanoparticles via a soft polyol method results in well-defined and stable Pt/Fe-N-C hybrids. The Pt addition strongly reduces the H2O2 production and Fe leaching rate during ORR, while post mortem Mössbauer spectroscopy reveals that the highly active but unstable Fe(III)N4 site is partially stabilized. The similar H2O2 electroreduction activity of Pt/Fe-N-C and Fe-N-C and other analyses point toward a long-distance electronic effect of Pt nanoparticles in stabilizing FeN4 sites. Computational chemistry reveals that spin polarization of distant Pt atoms mitigates the structural changes of FeN4 sites upon adsorption of oxygenated species atop Fe, especially in high-spin state.

Apex marine predators, such as toothed whales and large petrels and albatrosses, ingest mercury (Hg) primarily in the form of methylmercury (MeHg) via prey consumption, which they detoxify as tiemannite (HgSe). However, it remains unclear how lower trophic level marine predators, termed mesopredators, with elevated Hg concentrations detoxify MeHg and what chemical species are formed. To address this need, we used high energyresolution X-ray absorption near edge structure spectroscopy paired with nitrogen (N) and Hg stable isotopes to identify the chemical forms of Hg, Hg sources, and species-specific S202Hg isotopic values in emperor penguin, a mesopredator feeding primarily on Antarctic silverfish. The penguin liver contains variable proportions of MeHg and two main inorganic Hg complexes (IHg), Hg-dithiolate (Hg(SR)2) and Hg-tetraselenolate (Hg(Sec)4), each characterized by specific isotopic values (S202MeHg = 0.3 +/- 0.2 %o, S202Hg(SR)2 = -1.6 +/- 0.2 %o, S202Hg(Sec)4 = -2.0 + 0.1 %o). Using S15N as a tracer of food source, we show that Hg(SR)2 is likely not obtained through dietary intake, but rather is present as a biochemical demethylation product. Furthermore, on average, female penguins transferred Hg to the egg strictly as MeHg in the egg albumen but as mixtures of MeHg and IHg in the membrane (89% and 11 %, respectively) and yolk (32% MeHg and 68% Hg(Sec)4). Despite IHg species in eggs, MeHg is still the main species quantitatively transferred by the mother to the chick because of the disproportionate mass of the MeHg-rich albumen compared to the yolk. This work highlights the transformation of MeHg to Hg(SR)2 during demethylation for the first time in multicellular organisms, but further work is needed to understand the formation of Hg(SR)2 in the presence of relatively abundant Se biomolecules in lower trophic level predator species.