In situ soft X-ray spectroscopy provides direct insight into the electronic structure of electrocatalysts under realistic reaction conditions but remains technically challenging due to the need to combine aqueous electrochemistry with ultra-high-vacuum detection. Here, we present a mesoporous carbon-membrane working electrode assembly (WEA) that enables window-free in situ XPS and NEXAFS measurements during electrochemical reactions. The design integrates a Nafion proton-exchange membrane with a mesoporous carbon-ionomer contact layer and a thin IrO x catalyst layer, providing continuous electronic and protonic pathways and stable hydration through the membrane. By tuning the chamber water vapor pressure to 8 mbar, the WEA maintains a nanometer-thin water layer sufficient for the oxygen evolution reaction (OER) while preserving photoelectron detection efficiency. A robust peristaltic pump integrated with an alumina-bed water vapor dosing system maintains steady-state hydration at 6-10 mbar with <±0.1 mbar variation, enabling reproducible in situ spectra over extended periods. In situ Ir 4f and O 1s XPS reveal oxidation of Ir3+/Ir4+ to Ir4+/Ir5+ and dynamic changes in hydroxyl and lattice oxygen species, while O K-edge NEXAFS identify the formation of potential-stabilized μ2-O and μ1-O oxygen ligand species at OER. The WEA thus provides a quantitative, window-free platform for probing electrochemical interfaces under near-ambient conditions and establishes a general methodology for in situ soft X-ray studies of functional electrocatalysts, closely resembling the architecture and operation of industrial membrane-based water electrolyzers. This approach establishes a reliable methodology for coupling electrochemistry with the element specific soft X-ray spectroscopy under realistic reaction conditions.

Multiwavelength light emission was observed in undoped tin oxide thin films deposited by metal-organic chemical vapor deposition at temperatures ranging from 700 degrees C to 800 degrees C. This work presents the relationship between the presence and nature of defects in undoped SnO2 thin films and their emission properties. Blue and orange emissions were observed on SnO2 thin films using a He-Cd laser and an Xe lamp at an excitation wavelength of 325 nm, respectively. Systematic characterization and analysis techniques, including low-temperature photoluminescence at temperatures ranging from 77 K to 298 K and surface-sensitive techniques using brilliant synchrotron radiation facilities, were applied to elucidate the features and origin of emission in undoped SnO2 layers. Based on our results, surface and bulk oxygen and interstitial tin defects play an important role in multi-wavelength emission processes and can be separately activated by controlling the applied light source.

The importance of cluster-size effects in heterogeneous catalysis is now well recognized. X-ray photoelectron spectroscopy (XPS) is an obvious technique to study size-dependent changes in the chemical composition and electronic structure of catalyst nanoparticles. However, as XPS is an averaging technique based on the detection of electrons, experiments require a narrow distribution of cluster size and a conducting homogeneous support in order to avoid sample charging, which would prevent accurate measurements of chemical shifts. Traditional methods of catalyst synthesis by impregnation/calcination of support powders lead to very large particle size distributions (typically ±50%) and insulating samples. They therefore fail both of the above criteria and make it extremely difficult to extract precise sample characterisation. Here we present an alternative approach designed to enable XPS analysis in vacuum and under reaction conditions, whereby: (i) nanoparticles are synthesized by gas condensation and passed through a mass filter, which allows size selection in the range of 1 to 10 000 atoms with typically ±4% accuracy; (ii) these particles are deposited onto a thin Al2O3 film grown on Al foil, which mimics the properties of conventional alumina supports while being conductive enough to avoid any charging-related artefacts in the XPS spectra. In vacuum, size-dependent Pd 3d binding-energy shifts up to 1.65 eV were recorded for supported Pd nanoparticles. Changes in the chemical composition of Pd nanoparticles were studied by near-ambient pressure (NAP)-XPS under dry and wet reaction conditions for methane oxidation (CH4 + O2 [+H2O]) in the temperature range between 150 °C and 450 °C. Under dry reaction conditions large Pd particles appeared to oxidise almost fully to Pd(II), whereas smaller clusters showed a mix of Pd(0) and Pd(II) oxidation states. Under wet conditions, oxidation starts at lower temperatures and particles of all sizes were fully oxidised when the highest temperature was reached. Sintering during the temperature ramp cannot be excluded, especially for the smaller particles, and may be part of the reason for the different behaviour under wet conditions. This study clearly shows composition changes which are particle-size dependent and demonstrates the possibilities of fine-tuning catalytic activity if better size-control can be achieved in catalyst synthesis.

Oxidation states underpin the understanding of active states, reaction mechanisms and catalytic performance of electrocatalysts. However, determining them at complex solid-liquid interfaces is challenging. Here we use multimodal spectroscopy to investigate polarized iridium oxide (IrOx) electrodes, a model water oxidation catalyst, to identify potential-dependent iridium and oxygen oxidation states. By integrating multiple operando spectroscopies (optical (ultraviolet-visible), Ir L-edge and O K-edge X-ray absorption spectroscopy) with electrochemistry mass spectrometry and density functional theory calculations, we identify the sequential depletion of electron densities from the Ir5d band (corresponding to Ir3+→Ir4+→Ir5+), followed by electron removal from the O2p band, forming electrophilic oxygen species (O-1) due to enhanced Ir-O covalency and electronic state overlap. Time-resolved measurements reveal distinct lifetimes for Ir5+ and O-1 states under water oxidation conditions, Ir5+ remains unreactive whereas O-1 is consumed at a time constant commensurate with the reaction rate, indicating that O-1 drives the oxygen evolution reaction. These findings demonstrate the necessity of using multiple operando techniques to gain a unified understanding of the evolution of oxidation states and active sites with potential for water oxidation on oxide catalysts.

Anion interactions with cations/molecules are crucial across chemistry and biology: in battery electrolytes, synthesis, atmospheric processes, and protein denaturation. Selecting the optimum anion represents an immense challenge, as anion interactions are diverse and complex. Descriptors are needed that quantitatively capture the ability of anions to interact with cations and molecules. However, only a small number of experimental anion interaction descriptors exist, all with similar limitations. Here we show that core-level anion electron binding energies, EB(core,anion), can be used to produce a new atomic-level descriptor for each of the key donor elements for anion interactions (O, N, F, Cl, Br, I, S), the element-specific donor number (DNE-XPS). DNE-XPS descriptors are intrinsic, capturing the anion interaction abilities independent of any probe, countercation, or solvent. DNE-XPS descriptors are also interpretable, as EB(core,anion) and therefore DNE-XPS are proportional to the electrostatic potential at the specific donor atom nucleus. Experimental core-level X-ray photoelectron spectroscopy (XPS) is used to measure EB(core,anion) and therefore DNE-XPS. Furthermore, DNE-XPS descriptors are produced easily and at low cost using lone-anion-SMD (solvation model density) calculations, a significant advance on the current anion descriptors, greatly reducing and potentially removing the need for experimental anion characterization. This work will greatly facilitate anion selection, especially for complex anions capable of forming interactions through multiple different atoms. We envisage our calculation method enabling the production of a very large database of DNE-XPS for each key element, ideal for use as machine learning training data sets.

Describing lithium-based battery positive electrodes based on different transition metal or oxygen-redox regimes can cause confusion in understanding metal-ligand hybridization, oxygen dimerization and degradation processes. Therefore, it is urgent to investigate the electronic structure of these materials and identify the role each cation and anion has in charge compensation at the subnanoscale. Here, using X-ray resonance photoemission spectroscopy, single-impurity Anderson models, spectral simulations and theoretical calculations, we examine redox mechanisms in positive electrodes during lithium-based battery operation. This approach reconciles the redox description of two positive electrode active materials-LiMn0.6Fe0.4PO4 and LiNiO2-in terms of varying degrees of charge transfer using the Zaanen-Sawatzky-Allen framework. In LiMn0.6Fe0.4PO4, the lack of strong hybridization indicates that the capacity results from the depopulation of metal 3d states, that is, conventional metal redox. However, in cells with LiNiO2-based positive electrodes, negative charge transfer dominates, and redox occurs through the formation and elimination of ligand-hole states. These results clarify the role of oxygen in Ni-rich systems and provide a framework to explain how the charge/discharge capacities are linked to oxygen-dominated states in highly covalent systems, without the need to consider oxygen dimerization.

A combination of experimental methods and computational techniques have been used to investigate the composition of the zinc ferrite (ZnFe2O4) (111) single crystal surface under different preparation methods. Surface-sensitive XPS and NEXAFS measurements show that upon annealing in ultra-high vacuum (UHV), Zn depletion occurs, leading to the formation of an iron-rich (11 1) surface, whereas annealing in the presence of O2 gas maintains a more bulk-like ZnFe2O4 surface composition. Analysis of the Fe 2p photoemission (XPS) and Fe L edge X-ray absorption signals shows a clear difference in iron oxidation state and distribution between the two different preparation conditions. After annealing in UHV, a mixed Fe2+/Fe3+ oxidation state and a cation distribution like that of a magnetite (Fe3O4) structure is observed, whereas after annealing in oxygen gas only Fe3+, mostly in octahedral coordination, is observed, as expected for a ZnFe2O4 structure. Temperature-dependent XPS confirms significant Zn depletion in the near-surface region above 500 degrees C under UHV, with almost no Zn remaining at 600 degrees C; under an O2 atmosphere no zinc depletion is observed up to 600 degrees C. A theoretical model based on DFT simulations illustrates how reduction from ZnFe2O4 to Fe3O4 with formation of O2 and Zn gas is thermodynamically feasible under UHV conditions, whereas the same reaction is not favourable at higher oxygen partial pressures. Our findings demonstrate the strong impact that UHV treatment has on zinc ferrite surfaces, and cautions that UHV environments, routinely employed for surface analysis, can themselves induce substantial modifications to the surface, thereby complicating the interpretation of measurements in the context of catalytically relevant conditions.

Layered double hydroxides (LDH) based on transition metals are highly flexible in tailoring their dimensionality, lattice, and electronic structures, making them promising candidates as multifunctional 2D materials for the development of clean energy technologies and boosting the use of hydrogen as an energy vector. In this paper, strategic anion substitution in cobalt LDH is an appealing strategy to produce a material with two-fold functionality, electrochemical and magnetocaloric response, offering a sustainable alternative to existing electrocatalysts and cryogenic refrigerants. It is unambiguously demonstrated that (poly)oxomolybdate-based specimens interleave in Co LDH nanosheets up to a Co:Mo = 1:0.4 ratio, leading to an interstratified material. This intercalation greatly benefits the kinetics of the oxygen evolution reaction for H2 production, boosting the catalytic sites due to the expansion of the interlayer space, induced by the bulky molybdates which also partially modify the Co oxidation state of αCo(OH)2 nanolayers, favoring charge transfer. In parallel, the interleaved Mo species strengthen superexchange interactions compared with pristine α-Co(OH)2, effectively adjusting the operating temperature toward the liquid hydrogen range (2030 K). This specific temperature range allows to fill a critical gap in magnetocaloric materials, as few systems can simultaneously achieve both large magnetic entropy changes and structural stability.

Describing Li-ion battery positive electrodes in terms of distinct transition metal or oxygen redox regimes can lead to confusion in understanding metal-ligand hybridisation, oxygen dimerisation, and degradation. There is a pressing need to study the electronic structure of these materials and determine the role each cation and anion plays in charge compensation. Here, we employ transition metal L-edge X-ray Resonance Photoemission Spectroscopy in conjunction with Single Impurity Anderson models, Self-consistent Real Space Multiple Scattering spectral simulations, and Dynamical Mean-Field theory calculations to directly evaluate the redox mechanisms in (de-)lithiated battery electrodes. This approach reconciles the redox description of two canonical cathodes – LiMn_0.6Fe_0.4PO_4 and LiNiO_2 – in terms of varying degrees of charge transfer using the established Zaanen-Sawatzky-Allen framework, common to condensed matter physics. In LiMn_0.6Fe_0.4PO_4, the absence of charge transfer means capacity arises due to the depopulation of metal 3d states, i.e. conventional metal redox. Whereas, in LiNiO_2, charge transfer dominates and redox occurs through the formation and elimination of ligand hole states. This work clarifies the role of oxygen in Ni-rich system and provides a framework to explain how capacity can be extracted from oxygen-dominated states in highly covalent systems without needing to invoke dimerisation.

This study explores the effect of CeO2 doping on the catalytic performance of Fe, Co, and Ni catalysts supported on carbon nanofibers (CNFs) for hydrogen production via ammonia decomposition. Incorporating CeO2 significantly enhanced catalytic activity, achieving 90 % ammonia conversion at 600 degrees C. Stability tests confirmed sustained performance, maintaining high activity for at least 30 h on stream. A deep surface characterization revealed that the incorporation of Ni after the CeO2 doping created nanocatalytic portions of highly dispersed Ni/ CeO2 on the CNFs structure. This guaranteed an intimate contact between the Ni and the CeO2, resulting in an increase in the H2 production rate. Notably, Ni catalysts directly supported on bulk CeO2 exhibited inferior performance, likely due to low relative surface of available ceria. These findings highlight CeO2-doped CNFs as a promising platform for scalable, high-performance hydrogen production from ammonia.

A combination of experimental methods and computational techniques have been used to investigate the composition of the zinc ferrite (ZnFe2O4) (111) single crystal surface under different preparation methods. Surface-sensitive XPS and NEXAFS measurements show that upon annealing in ultra-high vacuum (UHV), Zn depletion occurs, leading to the formation of an iron-rich (111) surface, whereas annealing in the presence of O2 gas maintains a more bulk-like ZnFe2O4 surface composition. Analysis of the Fe 2p photoemission (XPS) and Fe L edge X-ray absorption signals shows a clear difference in iron oxidation state and distribution between the two different preparation conditions. After annealing in UHV, a mixed Fe2+/Fe3+ oxidation state and a cation distribution like that of a magnetite (Fe3O4) structure is observed, whereas after annealing in oxygen gas only Fe3+, mostly in octahedral coordination, is observed, as expected for a ZnFe2O4 structure. Temperature-dependent XPS confirms significant Zn depletion in the near-surface region above 500 °C under UHV, with almost no Zn remaining at 600 °C; under an O2 atmosphere no zinc depletion is observed up to 600 °C. A theoretical model based on DFT simulations illustrates how reduction from ZnFe2O4 to Fe3O4 with formation of O2 and Zn gas is thermodynamically feasible under UHV conditions, whereas the same reaction is not favourable at higher oxygen partial pressures. Our findings demonstrate the strong impact that UHV treatment has on zinc ferrite surfaces, and cautions that UHV environments, routinely employed for surface analysis, can themselves induce substantial modifications to the surface, thereby complicating the interpretation of measurements in the context of catalytically relevant conditions.

We report the rapid microwave-assisted solvothermal synthesis of a Cu-MOF (metal-organic framework) with open metal sites, focusing on understanding its CO2 capture properties in relation to phase purity and stability. A combined experimental and theoretical approach is used to identify the MOF's structural features involved in the adsorption process. Specifically, Cu(i) defects are found to play an important role in the CO2 adsorption process, with the Cu-1 sample, synthesized using an optimized ligand/Cu precursor ratio for the highest phase purity, exhibiting more abundant Cu(i) defects as well as the highest adsorption capacity. Grand canonical Monte Carlo simulations show that the Cu(i) sites exhibit a greater affinity for CO2 adsorption compared to the Cu(ii) sites. In situ soft and hard X-ray absorption fine structure spectroscopic techniques confirm the conversion of Cu(i) to Cu(ii) upon CO2 chemisorption, with this conversion being more pronounced in the core of the particles. The simulations are used to estimate the fraction of Cu(i) defects and Cu(ii) sites present within the Cu-1 and to validate the experimental isotherm. Overall, this study provides insights into the CO2 capture properties of this type of Cu-MOF and highlights the importance of phase purity and the role of defects in achieving high adsorption performance.

X-ray Photoelectron Spectroscopy (XPS) is a powerful tool for probing the chemical and electronic states of materials with elemental specificity and surface sensitivity. However, its application in the tender X-ray range (1–5 keV) for synchrotron radiation has remained limited due to the limited choice of optics capable of maintaining high reflectivity and efficiency in this energy window. To address this, multilayer (ML) grating structures have become increasingly popular, offering significantly higher efficiency than SL coatings in the tender X-ray region. This paper presents the development of ML laminar gratings optimised for enhancing efficiency in the tender X-ray range, and capable of retaining performance under intense X-ray exposure in the oxygen partial pressure of $$\sim$$ 10 $$^{-8}$$ mbar. The ML coating quality was verified through X-ray reflectivity (XRR), XPS and near-edge X-ray absorption fine structures (NEXAFS) measurements, while the performance of the grating was validated through beamline flux transmission and XPS measurements. The MLLG demonstrated $$\sim$$ 22 $$\times$$ higher intensity in flux and XPS, significantly improving the signal-to-noise ratio. Most importantly, the MLLGs outperformed traditional designs by offering improved spectral resolution while maintaining measurement capability at varying $$C_{ff}$$ values without compromising the intensity. Furthermore, we demonstrated that the incorporation of nitrogen during deposition further enhances flux transmission.

Metal-organic gels (MOGs) and their derived aerogels (MOAs) offer an alternative to crystalline MOFs, combining the coordination-driven tunability with the flexibility, hierarchical porosity, and easy processability of sol-gel polymers. Their noncrystalline nature enables the integration of functional units without crystallization constraints, facilitating diverse uses, and drawing recent attention for photocatalytic applications. Herein we report the design of a new approach to prepare a titanium-based MOA synthesized via a two-step strategy involving a preformed titanium oxo-cluster ([Ti8O8(benzoato)16]), and a subsequent ligand exchange with benzene-1,3,5-tricarboxylato ligands. A combined chemical, microstructural, and NEXAFS analysis confirms the retention of Ti8 cluster and the presence of uncoordinated -COOH groups after meso-macroporous gel formation. Those enabled a subsequent homogeneous incorporation of single-atom site co-catalysts via coordination with Ru, Co, Ni, and Cu complexes bearing terpyridine, bipyridine, and phenanthroline N-ligands. Photocatalytic hydrogen evolution under 365 nm LED irradiation exhibited significant activity (110 μmol·g-1·h-1), which further increased upon functionalization. The MOAs functionalized with Ru- and Cu-terpyridine complexes showed the highest performance (167 and 164 μmol·g-1·h-1, respectively), surpassing even Pt-loaded analogues and highlighting the role of terpyridine in facilitating multielectron storage. The system also showed stable long-term performance up to 24 h.

In Ni-rich layered oxide cathodes, cycling above the oxygen-loss threshold voltage (~4.3 V vs. Li+/Li) promotes structural transformations at the cathode surface. These transformations can result in various thermodynamically favorable rock-salt like (RSL) structures (NiO, NiOx, and/or LiyNizO) that have different Li+ transport properties. Elucidating the precise phase type in the RSL can help determine design strategies to improve Li+ kinetics and identify design rules to suppress capacity fade in Ni-rich cathodes. This study utilizes surface-sensitive X-ray absorption spectroscopy in combination with first principles simulations and distinguishes the layered oxide spectroscopic features from surface reduced layers of pure NiO and LixNi1-xO. The transport of lithium ions through this oxygen-loss-induced surface reconstructed layer is studied with operando X-ray diffraction in a pouch cell as a function of cycling aging and constant voltage protocols.

AbstractElectrochemical hydrogen peroxide (H2O2) production (EHPP) via a two-electron oxygen reduction reaction (2e- ORR) provides a promising alternative to replace the energy-intensive anthraquinone process. M-N-C electrocatalysts, which consist of atomically dispersed transition metals and nitrogen-doped carbon, have demonstrated considerable EHPP efficiency. However, their full potential, particularly regarding the correlation between structural configurations and performances in neutral media, remains underexplored. Herein, a series of ultralow metal-loading M-N-C electrocatalysts are synthesized and investigated for the EHPP process in the neutral electrolyte. CoNCB material with the asymmetric Co-C/N/O configuration exhibits the highest EHPP activity and selectivity among various as-prepared M-N-C electrocatalyst, with an outstanding mass activity (6.1 × 105 A gCo−1 at 0.5 V vs. RHE), and a high practical H2O2 production rate (4.72 mol gcatalyst−1 h−1 cm−2). Compared with the popularly recognized square-planar symmetric Co-N4 configuration, the superiority of asymmetric Co-C/N/O configurations is elucidated by X-ray absorption fine structure spectroscopy analysis and computational studies.

Amorphous porous boron nitride (BN) represents a versatile material platform with potential applications in adsorptive molecular separations and gas storage, as well as heterogeneous and photo-catalysis. Chemical doping can help tailor BN's sorptive, optoelectronic, and catalytic properties, eventually boosting its application performance. Phosphorus (P) represents an attractive dopant for amorphous BN as its electronic structure would allow the element to be incorporated into BN's structure, thereby impacting its adsorptive, optoelectronic, and catalytic activity properties, as a few studies suggest. Yet, a fundamental understanding is missing around the chemical environment(s) of P in P-doped BN, the effect of P-doping on the material features, and how doping varies with the synthesis route. Such a knowledge gap impedes the rational design of P-doped porous BN. Herein, we detail a strategy for the successful doping of P in BN (P-BN) using two different sources: phosphoric acid and an ionic liquid. We characterized the samples using analytical and spectroscopic tools and tested them for CO2 adsorption and photoreduction. Overall, we show that P forms P-N bonds in BN akin to those in phosphazene. P-doping introduces further chemical/structural defects in BN's structure, and hence more/more populated midgap states. The selection of P source affects the chemical, adsorptive, and optoelectronic properties, with phosphoric acid being the best option as it reacts more easily with the other precursors and does not contain C, hence leading to fewer reactions and C impurities. P-doping increases the ultramicropore volume and therefore CO2 uptake. It significantly shifts the optical absorption of BN into the visible and increases the charge carrier lifetimes. However, to ensure that these charges remain reactive toward CO2 photoreduction, additional materials modification strategies should be explored in future work. These strategies could include the use of surface cocatalysts that can decrease the kinetic barriers to driving this chemistry.

A-site doped SrTiO3 is considered as a promising substitute for traditional anodic metals in solid oxide fuel cells (SOFCs). In this study, we present the reactivity of La0.2Sr0.25Ca0.45TiO3 (LCSTO), La0.2Sr0.7TiO3 (LSTO), and SrTiO3 (STO) toward H2 by operando ambient pressure NEXAFS spectroscopy and theoretical spectra simulation with FDMNES code. The samples were synthesized by MBE (molecular beam epitaxy), hydrothermal, and modified-Pechini routes. We found that the reducibility of the samples depends not only on their stoichiometry but also on the morphology, which is determined by the synthetic method. The results of these experiments give insight into the reducibility of Ti4+ in perovskites as well as the opportunity to further optimize the synthesis of these materials to obtain the best performance for SOFC applications.