X-ray Absorption Spectroscopy Spectra Research Articles

Probing Isolated Water Molecules in Aqueous Acetonitrile Solutions Using Oxygen K-Edge X-ray Absorption Spectroscopy.

Oxygen K-edge X-ray absorption spectroscopy (XAS) of an aqueous acetonitrile solution exhibited a sharp peak at approximately 537 eV, which was similar to that of water vapor and was not observed in liquid water. The inner-shell spectra of isolated water molecules and water clusters of different sizes surrounded by acetonitrile molecules were obtained by extracting these water structures from the liquid structures of aqueous acetonitrile solutions, as calculated using molecular dynamics simulations. The sharp peak profiles of the O K-edge XAS spectra were derived not from water clusters but from isolated water molecules surrounded by acetonitrile molecules. The present study proposes that isolated water molecules are easily formed in aqueous acetonitrile solutions and that the electronic structures of the isolated water molecules can be analyzed using O K-edge XAS spectra, which separates the contributions of small water clusters.

Simulating X-ray Absorption Spectroscopy in Challenging Environments: Methodological Insights from Water-Solvated Ammonia and Ammonium Systems.

Core-electron excitations in solvated systems, influenced by solvent geometry and hydrogen bonding, make X-ray absorption spectroscopy (XAS) a valuable tool for assessing solvent-solute interactions. However, calculating XAS spectra with electronic-structure methods has proven challenging due to a delicate interplay between correlation and solvation effects. This study provides a computational procedure for XAS modeling in solvated systems, with water-solvated ammonia and ammonium systems serving as probes. Exploring methodological challenges, we investigate explicit embedding models, specifically the polarizable embedding family, including polarizable density embedding and extended polarizable density embedding. Our linear-response time-dependent density functional theory (LR-TDDFT) XAS calculations reveal the efficiency of this approach, with extended polarizable density embedding emerging as a robust improvement over polarizable density embedding. Contrary to some recent literature, our study challenges the belief that LR-TDDFT cannot accurately describe XAS spectra of ammonia and ammonium solvated in water.

A Versatile Electrochemical Cell for Operando XAS

AbstractIn situ and operando X‐ray absorption spectroscopy (XAS) provides fundamental insight into the working principles of electrocatalysts and is an important tool for future catalyst development. However, the design of an operando XAS electrocatalytic cell is not facile, and researchers designing cells, whether new cells or modifications to previous cells, often spend many hours on cell design before obtaining high‐quality XAS data. Here, we describe the design, with engineering drawings, and operation of a versatile XAS cell with options for gas flow, electrolyte flow, pH monitoring, temperature monitoring, and the ability to handle many catalyst forms (any catalyst that can be deposited onto a conductive X‐ray transparent substrate). We benchmarked XAS spectra collected using the new experimental cell to a previous cell design showing its ability to produce quality XAS data. We demonstrate the viability of this cell by providing insight into electrocatalysts by studying cation effects and show the tetrabutylammonium cation prevents bulk oxidation of copper. We hope the availability of this cell allows researchers to convert time typically spent on cell design to time spent on breakthroughs in electrocatalysis.

Geological and Crystallochemical Characterization of the Margaritasite–Carnotite Mineral from the Uranium Region of Peña Blanca, Chihuahua, Mexico

Margaritasite is a mineral compound discovered in the early 1980s in Chihuahua, Mexico. It is a natural cesium uranyl vanadate found only, so far, in the Margaritas mine of the Peña Blanca highlands. In this work, a thorough characterization of the aforementioned mineral is presented. The portfolio of the techniques employed includes high-resolution X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy, transmission electron microscopy in selected area electron diffraction (SAED) mode, and X-ray absorption spectroscopy (XAS). After extensive data analysis and modeling, new information on the mineral has been retrieved. Its phase composition is margaritasite–carnotite: a solid solution of cesium and potassium uranyl vanadate [(Cs,K)2(UO2)2(VO4)2·nH2O], and margaritasite, which is practically pure cesium uranyl vanadate [Cs2(UO2)2(VO4)2·nH2O]. The crystal structure of both components presents the space group P 1 21/c 1. Yet, each phase has similar, but appreciably different, lattice parameters. The mineral has a lamellar tabular and prismatic morphology. SAED patterns confirm the crystal structure of margaritasite. XAS spectra of Cs, V, and U confirm the elemental composition, oxidation states, and interatomic distances of this structure. These findings are consistent with the presence of cesium in this unique mineral from the paragenesis point of view.

In Solution Identification of the Lysine-Cysteine Redox Switch with a NOS Bridge in Transaldolase by Sulfur K-Edge X-ray Absorption Spectroscopy.

A novel covalent post-translational modification (lysine-NOS-cysteine) was discovered in proteins, initially in the enzyme transaldolase of Neisseria gonorrhoeae (NgTAL) [Nature 2021, 593, 460-464], acting as a redox switch. The identification of this novel linkage in solution was unprecedented until now. We present detection of the NOS redox switch in solution using sulfur K-edge X-ray absorption spectroscopy (XAS). The oxidized NgTAL spectrum shows a distinct shoulder on the low-energy side of the rising edge, corresponding to a dipole-allowed transition from the sulfur 1s core to the unoccupied σ* orbital of the S-O group in the NOS bridge. This feature is absent in the XAS spectrum of reduced NgTAL, where Lys-NOS-Cys is absent. Our experimental and calculated XAS data support the presence of a NOS bridge in solution, thus potentially facilitating future studies on enzyme activity regulation mediated by the NOS redox switches, drug discovery, biocatalytic applications, and protein design.

Liposomes as selenium nanocarriers for foliar application to wheat plants: A biofortification strategy

In the present work, liposomes have been used as nanocarriers in the biofortification of wheat plants with selenium (Se) through foliar application. Liposomal formulations were prepared using 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and Phospholipon®90H (P90H) (average size <100 nm), loaded with different concentrations of inorganic Se (selenite and selenate) and applied twice to the plants in the stage of vegetative growth. Liposomes enhanced Se uptake by wheat plants compared to direct application. The highest Se enrichment was achieved using the phospholipid DPPC and a concentration of 1000 μmol·L−1 of Se without affecting the biomass, chlorophylls, carotenoids, and the concentration of mineral nutrients of the plants. The chemical speciation of Se in the plants was further investigated by X-ray absorption spectroscopy (XAS). The results from XAS spectra revealed that most of the inorganic Se was transformed to organic Se and that the use of liposomes influenced the proportion of C-Se-C over C-Se-Se-C species.

In Situ X-ray Absorption Spectroscopy of LaFeO3 and LaFeO3/LaNiO3 Thin Films in the Electrocatalytic Oxygen Evolution Reaction.

We study the electrocatalytic oxygen evolution reaction using in situ X-ray absorption spectroscopy (XAS) to track the dynamics of the valence state and the covalence of the metal ions of LaFeO3 and LaFeO3/LaNiO3 thin films. The active materials are 8 unit cells grown epitaxially on 100 nm conductive La0.67Sr0.33MnO3 layers using pulsed laser deposition (PLD). The perovskite layers are supported on monolayer Ca2Nb3O10 nanosheet-buffered 100 nm SiNx membranes. The in situ Fe and Ni K-edges XAS spectra were measured from the backside of the SiNx membrane using fluorescence yield detection under electrocatalytic reaction conditions. The XAS spectra show significant spectral changes, which indicate that (1) the metal (co)valencies increase, and (2) the number of 3d electrons remains constant with applied potential. We find that the whole 8 unit cells react to the potential changes, including the buried LaNiO3 film.

New Design PdNi Heterogeneous Nanocatalysts for the Direct Synthesis of Hydrogen Peroxide

Hydrogen peroxide (H2O2) is a widely used chemical as an eco-friendly oxidizing agent, with water being the only byproduct of oxidation in applications like bleaching pulp and paper, making electronic semiconductors, chemical and detergent synthesis, and wastewater treatment. The direct synthesis approach is preferred to provide the environmentally friendly production of H2O2 for market requirements. Bimetallic PdNi nanocatalysts were chosen for this study because of their catalytic activity and the structural characteristics of the material system. First, for the development of order-structured bimetallic PdNi nanocatalysts based on mesoporous carbon template after hydrogen-assisted heat treatment at 750∘C. The transformation of the disordered structure into ordered intermetallically structured PdNi alloys with higher alloying extents was confirmed by X-ray absorption spectroscopy (XAS) and high-resolution transition electron microscopy (HR-TEM). Then, to improve the oxygen oxidation reaction, two-electron pathway selectivity was used by TiO2-C as a support-ordered structure material to facilitate strong metal-support interactions. XAS and X-ray photoelectron spectra (XPS) techniques show more clear evidence of metal-support interactions with electron transfer from defects in the TiO2-C support to the ordered alloyed PdNi nanocatalysts, resulting in record productivity and selectivity of H2O2 production at ambient conditions. The results demonstrated in this study will enlighten a reliable design of new heterogeneous nanocatalysts with ordered structure. Electron transfer between hybrid support and active sites can clarify the catalytic behavior and prompt further research during the direct synthesis of hydrogen peroxide.&#x0D; Keywords: hydrogen peroxide, direct synthesis, heterogeneous nanocatalysts PdNi, TiO2-C

Coupled Experimental-Theoretical Characterization of a Carbon Electrode in Vanadium Redox Flow Batteries using X-ray Absorption Spectroscopy.

Vanadium redox flow batteries (VRFBs) have emerged as promising solutions for stationary grid energy storage due to their high efficiency, scalability, safety, near room-temperature operation conditions, and the ability to independently size power and energy capacities. The performance of VRFBs heavily relies on the redox couple reactions of V2+/V3+ and VO2+/VO2+ on carbon electrodes. Therefore, a thorough understanding of the surface functionality of carbon electrodes and their propensity for degradation during electrochemical cycles is crucial for designing VRFBs with extended lifespans. In this study, we present a coupled experimental-theoretical approach based on carbon K edge X-ray absorption spectroscopy (XAS) to characterize carbon electrodes prepared under different conditions and identify relevant functional groups that contribute to unique spectroscopic features. Atomic models were created to represent functional groups, such as hydroxyl, carboxyl, methyl, and aldehyde, bonded to carbon atoms in either sp2 or sp3 environments. The interactions between functionalized carbon and various solvated vanadium complexes were modeled using density functional theory. A library of carbon K-edge XAS spectra was generated for distinct carbon atoms in different functional groups, both before and after interacting with solvated vanadium complexes. We demonstrate how these simulated spectra can be used to deconvolve ex situ experimental spectra measured from carbon electrodes and to track changes in the electrode composition following immersion in different electrolytes or extended cycling within a functional VRFB. By doing so, we identify the active species present on the carbon electrodes, which play a crucial role in determining their electrochemical performance.

A step towards understanding plastic complexity: Antimony speciation in consumer plastics and synthetic textiles revealed by XAS

We identified the antimony species present in a wide variety of plastic samples by X ray absorption spectroscopy (XAS) at the Sb L3-edge. The samples contained different concentrations of antimony (Sb), ranging from PET bottles in which Sb compounds are used as catalysts, with concentrations around 300 mg/kg, to electrical equipment in which the element is used as a flame retardant, with concentrations of several tens of thousands of mg/kg. Although the shape of the spectra at the L3-edge is quite similar for all Sb reference materials, we were able to identify antimony glycolate or acetate in PET bottles, bound organic Sb in c-PET trays and senarmontite in electrical materials as the main Sb components. In samples with high Ca content (e.g., electrical objects, some c-PET food trays and textiles) the Ca Ka emission line interferes with the Sb La line by introducing a high background which reduces the signal-to-noise ratio in the Sb XAS spectrum, resulting in noisy and distorted spectra. The element-resolved map on a PET bottle sample revealed both Sb and Ca hot spots of around 10-20 microns in size, with no correlation.

Monolayer calibration of endofullerenes with x-ray absorption from implanted keV ion doses

X-ray absorption spectroscopy (XAS) has the highest sensitivity for chemical element detection on surfaces. With this approach, small amounts of lanthanide-containing endofullerene molecules (Ho3N@C80) have been measured by total electron yield at a low flux bending magnet beamline. The monolayer coverage is calibrated by extrapolating the signals of constant doses (3×1014 cm−2) of Ho ions implanted into SiO2 with energies between 2 and 115 keV. At room temperature, the Ho XAS spectra of the molecules and implanted ions indicate trivalent but not identical Ho ground states. Still, this approach demonstrates a way for calibration of small coverages of molecules containing open core-shell elements.

Interfacial electronic state between hexagonal ZnO and cubic NiO.

The interface of two dissimilar materials gives rise to a myriad of interesting structural, magnetic, and electronic properties that may be utilized to produce novel materials with unique characteristics and functions. In particular, growing a cubic oxide film on top of a hexagonal oxide substrate results in such unique properties due to the conflict of their respective stabilization mechanisms within the interface layer. This study aims to elucidate the electronic properties of the interface between hexagonal ZnO and cubic NiO by analyzing the interface electronic states within epitaxial NiO films grown on ZnO substrates, expressed in the form of ultraviolet photoemission spectroscopy (UPS) for valence band structure and X-ray absorption spectroscopy (XAS) spectra for conduction band structure. This is accomplished through a modeling approach in which the film, substrate, and interface signals are assumed to be related to each other by a set of mathematical equations, and then rearranging and modulating the equations to obtain unique UPS and XAS spectra that depict the interface electronic states.

Assembling Fe4 single-molecule magnets on a TiO2 monolayer.

The decoration of technologically relevant surfaces, such as metal oxides, with Single-Molecule Magnets (SMMs) constitutes a persistent challenge for the integration of these molecular systems into novel technologies and, in particular, for the development of spintronic and quantum devices. We used UHV thermal sublimation to deposit tetrairon(III) propeller-shaped SMMs (Fe4) as a single layer on a TiO2 ultrathin film grown on Cu(001). The properties of the molecular deposit were studied using a multi-technique approach based on standard topographic and spectroscopic measurements, which demonstrated that molecules remain largely intact upon deposition. Ultralow temperature X-ray Absorption Spectroscopy (XAS) with linearly and circularly polarized light was further employed to evaluate both the molecular organization and the magnetic properties of the Fe4 monolayer. X-ray Natural Linear Dichroism (XNLD) and X-ray Magnetic Circular Dichroism (XMCD) showed that molecules in a monolayer display a preferential orientation and an open magnetic hysteresis with pronounced quantum tunnelling steps up to 900 mK. However, unexpected extra features in the XAS and XMCD spectra disclosed a minority fraction of altered molecules, suggesting that the TiO2 film may be chemically non-innocent. The observed persistence of SMM behaviour on a metal oxide thin film opens new possibilities for the development of SMM-based hybrid systems.

Quantitative in situ synchrotron X-ray analysis of the ALD/MLD growth of transition metal dichalcogenide TiS2 ultrathin films.

We present the results of a full quantitative analysis of X-ray absorption spectroscopy (XAS) performed in situ during the growth of ultrathin titanium disulfide (TiS2) films via an innovative two-step process, i.e. atomic layer deposition/molecular layer deposition (ALD/MLD) followed by annealing. This growth strategy aims at separating the growth process from the crystallization process by first creating an amorphous Ti-thiolate that is converted later to crystalline TiS2via thermal annealing. The simultaneous analysis of Ti and S K-edge XAS spectra, exploiting the insights from density functional theory calculations, allows us to shed light on the chemical and structural mechanisms underlying the main steps of growth. The nature of the bonding at the base of the interface creation with the SiO2 substrate is disclosed in this study. Evidence of a progressive incorporation of S in the amorphous Ti-thiolate is given. Finally, it is shown that the annealing step plays a critical role since the transformation of the Ti-thiolate into nanocrystalline TiS2 and the loss of S are simultaneously induced, validating the two-step synthesis approach, which entails distinct growth and crystallization steps. These observations contribute to a deeper understanding of the bonding mechanism at the interface and provide insights for future research in this field and the generation of ultra-thin layered materials.

Influence of strong π-acceptor ligands on Cr-K-edge X-ray absorption spectral signatures and consequences for the interpretation of surface sites in the Phillips catalyst.

X-ray absorption spectroscopy (XAS) has been central to the study of the Phillips polymerization catalyst (CrO3/SiO2). As Cr K-edge XAS signatures are sensitive to the oxidation state, geometry and types of ligands on surface (active) sites, the superposition of these effects makes their interpretation challenging. Notably, CO has been particularly used as a reductant to generate low valent Cr sites from CrO3/SiO2 and as a structural IR probe for analysing reduced Cr surface sites. Hence, it is essential to establish a solid understanding of the spectroscopic impact of CO on low-valent Cr sites. We thus built a series of fully characterized low-valent Cr molecular compounds bearing isoelectronic isocyanide ligands in place of CO, with the goal of understanding the effect of the coordination of π-acceptor ligands on the XANES signature of Cr sites. Cr K-edge spectra supplemented with DFT calculations elucidate the effect of the coordination of π-acceptor ligands on XAS signatures, giving a sharp resonance at the white line while modifying the fine structure due to short Cr-C distances and stability of low-spin Cr(ii/iii) species. The isocyanide references allow the deconvolution of the XAS spectra of the reduced CrO3/SiO2 catalyst by evaluating the types of surface species and relative amounts of bound CO at different CO pressures and temperatures.

Effect of Dissolved Gases on Pt Nanoparticle Catalysts Investigated By in Situ SAXS, XAS Measurements

Understanding of the structural and the chemical properties of Pt catalysts in polymer electrolyte fuel cells (PEFCs) is necessary to improve the activity for the durability of the catalysts. The small-angle X-ray scattering (SAXS) and the X-ray absorption spectroscopy (XAS) measurements are widely used to investigate these properties. We developed a system that combines in situ A-SAXS/XAS measurements in the same field of observation using a channel flow electrode (CFE) cell and characterized the chemical states, average diameter and size distributions of Pt catalysts under controlled electrochemical conditions. In this study, we investigated an effect of dissolved gases on Pt nanoparticle catalysts using the system.All experiments were carried out at SPring-8 BL19B2. A commercial Pt/carbon black catalyst (TEC10E50E, Tanaka Kikinzoku Kogyo) was used as test electrode in this experiment. Prior to SAXS and XAS measurements, the electrochemical potential was cycled between 0.6 and 1.0 V vs. the RHE in O2 or N2-saturated 0.1 M HClO4. For the XAS measurements, the Pt LⅢ edge was used. The ionization chamber and a seven-elements silicon drift detector were used to obtain the XAS spectra. For the SAXS measurements, the X-ray energy was set to 11.5 keV and 11.55 keV, which are below and near to the Pt LIII absorption edge, respectively. The scattered X-ray was detected using an area detector (PILATUS 2M). Figure 1 show the X-ray absorption near edge structure (XANES) spectra of the Pt catalyst after the potential cycles in O2-saturated 0.1 M HClO4. The white-line peak intensity increased and became higher at a higher potential cycle. This indicates the partial electron-transfer from Pt atoms or initial stage of Pt oxidation. We also will discuss the effect of dissolved gases for morphological and chemical states from SAXS and XAS data. Figure 1

X-Ray Absorption Spectroscopy Studies of Ti-Mn Redox Flow Battery to Clarify the Redox Reaction

Redox flow battery (RFB) is a promising candidate of large-scale stationary energy storage which is necessary to utilize renewable energy. For RFBs, the capability to easily increase the capacity by enlarging the electrolyte tank, high charge-discharge cycle performance, and wide flexibility to high- and low-frequency fluctuations are highly advantageous.Nowadays vanadium RFBs are used for practical use, but the material cost of vanadium is problematic to further spread them. An alternative candidate for commercial use is titanium-manganese (Ti-Mn) RFBs [1] whose material cost should be lower. On the other hand, the stability of the electrolyte for positive electrode (catholyte) need to be improved, because precipitates are created by a charge disproportionation reaction of Mn ions in the charged catholyte [2]. The formation of precipitates decreases the energy density and degrades the cyclability. To improve the characteristics, the chemical state and redox reaction of the electrolytes of Ti-Mn RFBs should be clarified by precise analyses.We performed synchrotron radiation X-ray absorption spectroscopy (XAS) for the electrolytes of a Ti-Mn RFB to directly observe the redox reaction [3]. In this study, the same Ti-Mn RFB electrolyte was used for both positive and negative electrodes. The Ti K-edge XAS of the electrolyte for negative electrode (anolyte) revealed gradual reduction reaction of Ti from Ti4+ on the charge process. The Ti L 2,3-edge XAS spectrum for the anolyte at state of charge (SOC) of 80% was mostly attributed to Ti3+ state. The results for Ti are consistent with electrochemical views in previous reports [2]. The Mn K-edge XAS of the catholyte gradually shifted to higher energy-side up to SOC of 50%, indicating a slight oxidation reaction of Mn from Mn2+. However, the Mn L 2,3-edge XAS spectrum for the catholyte solution at SOC of 80% was of Mn2+ state that was not changed from the initial state. Instead, scanning transmission X-ray microscopy (STXM; XAS mapping with a high spatial resolution) at the Mn L 3-edge unveiled that the precipitates mostly consist of Mn4+. Thus, the charge disproportionation reaction of 2Mn3+ -> Mn2+ (solution) + Mn4+ (precipitates) in the charged catholyte was confirmed. In the presentation, the electronic-structure change of the Ti and Mn ions in both catholyte and anolyte will be discussed in detail.

Operando High-Temperature X-Ray Absorption Spectroscopy of LiNiO2 Cathode Material during Synthesis

The increasing demand for higher energy density in batteries for automotive applications has led to a trend toward increasing the Ni content in layered oxide cathode materials to increase their reversible capacity. However, LiNiO2, which has the highest Ni content, shows a faster capacity drop during charge-discharge cycling, which is attributed to its inherent structural instability in both the pristine and delithiated states. Therefore, to address the former issue and to better understand the appropriate synthesis conditions for LiNiO2, we have studied the changes in the local structure of LiNiO2 during the synthesis process using operando analysis techniques. Recently, high temperature in situ X-ray diffraction during LiNiO2 synthesis was reported by Bianchini [1] and Weber [2], which confirmed the loss of lithium and oxygen and the migration of Ni to Li layers above 700 °C. To further understand the mechanism of Li/Ni mixing and oxygen loss, operando high-temperature X-ray absorption spectroscopy (XAS) was performed during the synthesis of LiNiO2 to clarify the electrical structure of Ni at high temperatures. Pre-heated Li x NiO2 (x = 0.76, 1.01, 1.26, and 1.51) precursors were prepared by heating LiOH·H2O and Ni(OH)2 at 480 °C for 24 h in air. The precursor was pelletized and set in a quartz sample holder. Operando high-temperature Ni K-edge XAS spectra of the precursor were obtained at BL9A and BL12C in Photon Factory (PF), High Energy Accelerator Research Organization (KEK) by a transmission mode. The operando spectra of all samples except Li/Ni = 0.76 revealed a clear edge shift to the lower energy side corresponding to nickel reduction above 700 °C. The Li/Ni = 0.76 sample has a lithium-deficient composition and Ni is not oxidized to Ni3+ below 700 °C, so the Li/Ni = 0.76 sample has almost no Ni K-edge energy shift above 700 °C. These results suggest that Ni in LiNiO2 is reduced above 700 °C even in an oxygen atmosphere, regardless of whether the Li/Ni ratio is greater than 1. The Ni reduction above 700 °C is probably the cause of the Li/Ni mixture.Reference[1] M. Bianchini, J. Janek, et al., Angew. Chem., Int. Ed., 58, 10434 (2019).[2] R. Weber, J. R. Dahn, et al., J. Electrochem. Soc., 167, 100501 (2020).

Structure and chemical durability improvement of alkali silicate glass by zirconium dioxide and erbium oxide addition

Glass structure tailoring of alkali silicate glasses by addition of ZrO2 and Er2O3 is found to enhance the chemical durability of glasses. ZrO2 (x ranged between 5 mol% to 15 mol%) and Er2O3 (y ranged between 0.5 mol% to 1.5 mol%) were used to replace SiO2 and Na2O, respectively, in the glasses with the nominal composition of 10Li2O-(15-y)Na2O-10CaO-(65-x)SiO2-xZrO2-y Er2O3. The samples were prepared by conventional melt quenching technique. The structures of produced glasses were examined by X-ray absorption spectroscopy (XAS) and Raman spectroscopy. XAS spectra demonstrated that the oxidation numbers of Zr and Er ions were +4 and +3, respectively. The chemical environment around both cations was six-fold coordination. In addition, Raman spectra demonstrated that the Zr4+ ions formed the Q4(Zr) structure, which caused the reduction of non-bridging oxygen. In case of the Er3+ ions, the formation of the Si-O-Er bonds was explained from the Raman study. The chemical durability of glass was determined from Na+ ions leaching values. In pH 7 solution, the leached Na+ ions reduced from 25.67% to 21.43% and from 22.50% to 20.49% as a function of concentration of ZrO2 (x = 5 mol% to 15 mol%) and Er2O3 (y = 0.5 mol% to 1.5 mol%), respectively. As the results, the chemical durability of the ZrO2-containing and Er2O3-containing glasses were significantly improved due to charge compensated mechanism and enhancing network rigidity by increasing cation field strength. Moreover, the micro-hardness (580 HV to 837 HV) and density (2.54 g⸳cm-3 to 2.82 g⸳cm-3) also displayed an increased tendency with larger concentration of ZrO2 and Er2O3.

Real-time observation of intermediate species in electrochemical oxygen evolution reactions on CoOx through soft X-ray absorption spectroscopy

Real-time monitoring of oxygen species during the oxygen evolution reaction (OER) on cobalt oxide, one of the major OER electrocatalysts, was achieved through operando observation using wavelength-dispersive X-ray absorption spectroscopy (XAS) at the oxygen K-edge. The XAS spectra were collected every 3 s during electrode potential sweeping for the OER, and oxygen intermediate species related to the rate-determining step of the OER were detected just below the onset potential. Moreover, the cobalt L-edge XAS results demonstrate that the Co3O4 species dominates the surface of the electrode at a relatively high potential region, where the OER occurs. The present technique has significant potential for application in the analysis of solid–liquid interfaces, whose fundamental understanding is useful for further improvement of electrocatalysis.