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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Resolving local structural motifs across the phase evolution of zinc titanates with computational x-ray absorption spectroscopy

Resolving the local structure motifs that characterize phase evolution as a function of composition is a key challenge in structure characterization of complex materials. Here, in this study, we combine first-principles simulations and x-ray absorption near-edge structures (XANES) analysis to gain insights into the structure evolution revealed by measurements across a combinatorial zinc titanate thin film, which was grown with smoothly varying composition over a wide range of the Ti:Zn ratio. Specifically, we propose a cluster blind-signal-separation (cBSS) method for XANES spectral analysis based on a library of the structures and spectra of representative local motifs. In addition to motifs from zinc titanate crystals, two types of Ti-defect models constructed in this study are key to the understanding of the structure characteristics in the Zn-rich region. The cBSS method makes use of both spectral clustering of the simulated site-XANES spectra library and the BSS procedure to construct high-fidelity spectral basis functions from an experimental spectral sequence. The method provides a rigorous measure of the spectral sensitivity and basis completeness. The results of the XANES analysis are corroborated with other experimental modalities, including x-ray diffraction and spectroscopic ellipsometry, to validate the cBSS method. The calculated motif weights resulting from fitting the XANES spectra with the cBSS basis probe the atomic structure characteristics of both crystalline and amorphous phases as a function of the Ti/Zn composition. The insights of the local structure motif evolution are pivotal to the understanding of the nonmonotonic trend in the optical gap, which may lead to potential applications through tuning the optical properties of zinc titanate. The workflow of the XANES spectral analysis developed in this work can be generalized to construct the structure-property relationship in a broad material space.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Voltage and temperature effects on low cobalt lithium-ion battery cathode degradation

Degradation of low cobalt lithium-ion cathodes was tested using a full factorial combination of upper cut-off voltage (4.0 V and 4.3 V vs. Li/Li + ) and operating temperature (25 °C and 60 °C). Half-cell batteries were analyzed with electrochemical and microstructural characterization methods. Electrochemical performance was assessed with galvanostatic cycling, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) supported by distribution of relaxation times (DRT) analysis. Electrode microstructure was characterized with scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray absorption near edge structure (XANES) imaging. Higher cut-off voltage cycling shows presence of NiO x formation, a low diffusivity rock-salt phase, in both CV and XRD data. XRD patterns confirmed that the rock-salt phase was beginning to form at the low cut-off voltage at high temperature, but in much lower intensity than at the high cut-off voltage. Higher temperature accelerates degradation processes at both voltages. Degradation factors at high temperature include NiO x formation, cathode material dissolution, and electrolyte decomposition. SEM analysis suggests that supporting phases may isolate and disconnect active material particles reducing capacity retention and battery life cycle. DRT analysis and XANES imaging show that both high temperature samples revealed a NiO x phase based on an increased diffusive impedance and a visible shift in the XANES spectra. The low cut-off voltage, high temperature sample showed a split peak and shift to lower energies indicating early formation of the NiO x phase. The diffusive impedance, which hinders intercalation and deintercalation, is driven by the formation of the NiO x phase. While primarily driven by cut-off voltage, elevated temperature also contributes to this degradation mechanism.

electrochemical impedance spectroscopy↗
DOE OSTI2025

In-situ monitoring of atomically dispersed Pt sites supported on OMS-2 during CO 2 activation

Atomically dispersed catalysts have drawn great interest lately, as they showcase a high density of active sites, selectivity, and high turnover frequencies in oxidation chemistry due to labile oxygen activation. In contrast, the applications of these catalysts have lagged in reduction reactions due to the ambiguity caused by the sintering and restructuring of active sites. To bridge this gap, the evolution of Pt 4+ isomorphically substituted into an octahedral molecular sieve structure (OMS-2) under reductive conditions was correlatively characterized using multiple in-situ analytical techniques such as ambient pressure X-ray photoelectron spectroscopy, environmental transmission electron microscopy, and solid-state nuclear magnetic resonance. The surface dynamics of the Pt single atoms were revealed during the Reverse Water Gas Shift (RWGS) reaction, where the active sites were identified as two-coordinated platinum single atoms. Under reaction, we show nonbinding atoms adjacent to the single atoms restructured the motif of the single atoms to Pt 2+ via ion mobility of potassium, increasing the activation energy by 25.6 kJ/mol. Here, this work also highlights the potential for increased stability of the single atom sites via isomorphic substitution of the metal oxide support, since the Pt-OMS-2 catalyst retained activity for about 33 h before deactivation, after which nanoparticles were observed in TEM images. This work offers a new perspective in single atom synthesis using the metal oxide as the host for the single atom site, instead of adatoms on the surface

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Synthesis, Structure, and Redox Reactivity of Ni Complexes Bearing a Redox and Acid–Base Non-innocent Ligand with Ni II , Ni III , and Ni IV Formal Oxidation States

Here, a series of Ni complexes bearing a redox and acid–base noninnocent tetraamido macrocyclic ligand, H 4 -(TAML-4) {H 4 -(TAML-4) = 15,15-dimethyl-5,8,13,17-tetrahydro-5,8,13,17-tetraaza-dibenzo[a,g]cyclotridecene-6,7,14,16-tetraone}, with formal oxidation states of Ni II , Ni III , and Ni IV were synthesized and characterized structurally and spectroscopically. The X-ray crystallographic analysis of the Ni complexes revealed a square planar geometry, and the [Ni(TAML-4)] complex with the formal oxidation state of Ni IV was characterized to be [Ni III (TAML-4 •+ )] with the oxidation state of the Ni III ion and the one-electron oxidized TAML-4 ligand, TAML-4 •+ . The Ni III oxidation state and the TAML-4 radical cation ligand, TAML-4 •+ , were supported by X-ray absorption spectroscopy and density functional theory calculations. The reversible interconversions between [Ni II (TAML-4)] 2– and [Ni III (TAML-4)] − and between [Ni III (TAML-4)] − and [Ni III (TAML-4 •+ )] were demonstrated in spectroelectrochemical measurements as well as in chemical oxidation and reduction reactions. The reactivities of [Ni III (TAML-4)] − and [Ni III (TAML-4 •+ )] were then investigated in hydride transfer reactions using NADH analogs. Hydride transfer from 9,10-dihydro-10-methylacridine (AcrH 2 ) to [Ni III (TAML-4 •+ )] was found to proceed via electron transfer (ET) from AcrH 2 to [Ni III (TAML-4 •+ )] with no deuterium kinetic isotope effect (k H /k D = 1.0(2)). In contrast, hydride transfer from AcrH 2 to [NiIII(TAML-4)] − proceeded much more slowly via a concerted proton-coupled electron transfer (PCET) process with k H /k D = 7.0(5). In the latter reaction, an electron and a proton were transferred to the Ni III center and the TAML-4 ligand, respectively. The mechanisms of the ET by [Ni III (TAML-4 •+ )] and the concerted PCET by [Ni III (TAML-4)] − were ascribed to the different redox potentials of the Ni complexes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Frameshifting Stimulatory Sequence Induces Large Structural Change of Ribosomal Proteins When Bound to E. coli Ribosomes

Biological macromolecular machines occupy a continuum of structural conformations to perform cellular tasks. Mapping this conformational space provides an insight into its functionality. While the cryo-electron microscopy resolution revolution has expanded our ability to characterize the conformational continuums, there are obstacles in structurally characterizing regions of high flexibility. These technical barriers have impeded characterization of flexible ribosomal proteins when the ribosome is interacting with mRNA stem-loop structures such as a frameshifting stimulatory sequence (FSS). Small-angle neutron/X-ray scattering and electron microscopy were used to study ribosomal samples and compared structural differences between a ribosome that is bound to an FSS stem-loop compared to a ribosome bound to linear mRNA. This comparison shows that a large protein stalk elongates by 22% when the 70S interacts with an mRNA stem-loop. Finally, our results suggest that ribosomal proteins have extensive flexibility and may influence important ribosomal mechanisms, such as those that involve FSS.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Phase Transitions of Eutectic High Entropy Alloy AlCoCrFeNi 2.1 Under Shock Compression

High entropy alloys (HEAs) are a new class of metals that exhibit unique mechanical performance. Among HEAs, additively manufactured eutectic high entropy alloys (AM EHEAs) have recently emerged as candidate materials for use in extreme conditions due to their simultaneous high strength and ductility. However, the deformation and structural evolution of AM EHEAs under conditions of high pressure have not been well characterized, limiting their use in extreme applications. Dynamic compression experiments and molecular dynamics simulations are presented to study the structural evolution of AM EHEA AlCoCrFeNi 2.1 when compressed to pressures up to 400 GPa. In situ X-ray diffraction measurements capture the appearance of face-centered cubic and body-centered cubic phases at different pressure conditions, with pure- and mixed-phase regions. Furthermore, understanding the phase stability and structural evolution of the AM EHEA offers new insights to guide the development of high-performance complex materials for extreme conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Unveiling the Mechanism of Mn Dissolution Through a Dynamic Cathode‐Electrolyte Interphase on LiMn2O4

Abstract Understanding the formation and evolution of the cathode‐electrolyte interphase (CEI), which forms at the interface between the cathode and electrolyte, is crucial for revealing degradation mechanisms in cathode materials, especially for developing strategies to stabilize the interphase in the strongly oxidizing conditions that evolve at high operating voltages in next‐generation Li‐ion batteries. However, The present understanding of the CEI is challenged by its complex and dynamic nature. In this work, near‐edge X‐ray absorption fine structure spectroscopy, electrochemical characterization, and reactive molecular dynamics simulations are combined to reveal a mechanism for CEI formation and evolution above model LiMn 2 O 4 (LMO) thin‐film electrodes in contact with conventional carbonate‐based electrolytes. It is found that Mn dissolution from LMO can be understood in terms of repetitive Mn 3 O 4 formation and dissolution behavior during cycling, which is closely connected to electrolyte decomposition and a key aspect of the CEI formation and growth. The behavior of the CEI in this model system offers detailed insight into the dynamic chemistry of the interphase, underscoring the important role of electrolyte composition and cathode surface structure in interphase degradation.

Ou, Wenhan↗
DOE OSTI2025

Mechanism of O 2 Activation and Cysteine Oxidation by the Unusual Mononuclear Cu(I) Active Site of the Formylglycine-Generating Enzyme

The formylglycine-generating enzyme (FGE) catalyzes the selective oxidation of a peptidyl-cysteine to form formylglycine, a critical cotranslational modification for type I sulfatase activation and a useful bioconjugation handle. Previous studies have shown that the substrate peptidyl-cysteine binds to the linear bis-thiolate Cu(I) site of FGE to form a trigonal planar tris-thiolate Cu(I) structure that activates O 2 for the oxidation of the C β –H of the cysteine substrate via an unknown mechanism. Here, we employed a combination of stopped-flow kinetic, spectroscopic (UV–vis absorption, XAS, and EPR), and computational (DFT/TD-DFT calculations) methods to observe and characterize the key intermediates in this reaction for FGE from Streptomyces coelicolor. Our results define the reaction coordinate of FGE, which involves H-atom abstraction from the C β –H bond of the cysteine substrate by a reactive Cu(II)–O 2 •– species to form the now experimentally observed Cu(I)–OOH intermediate bound to a peptidyl-thioaldehyde, which proceeds to oxidize one of the protein-derived cysteine residues to a sulfenate that is end-on O-coordinated to Cu(I). These results provide fundamental insights into how the unusual mononuclear Cu(I) site of FGE activates O 2 for cysteine oxidation and stores oxidizing equivalents during catalysis by employing a Cu(I)–sulfenate intermediate with an end-on O-coordination that is unprecedented in biology.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Monolayer TiS 2 Nanosheets on Au(111)–Structural Characterization and Effect of Edge Stability for Shape Control

Transition metal dichalcogenides are promising alternatives to noble metal catalysts, e.g., for (photo-)activation of greenhouse gases or hydrogenations. Herein, a direct synthetic route for 2D TiS 2 nanosheets on Au(111) by titanium deposition in the presence of a mild, organic, non-oxidizing sulfur source is presented. High-resolution scanning tunneling microscopy (STM) is used to gain atomic-level insights into the TiS 2 nanosheet morphology. In contrast to the literature, this protocol gains mostly hexagonal and truncated triangular nanosheets with an increased edge contrast in STM, analog to metallic edge states in MoS 2 . Synchrotron-based photoelectron spectroscopy allows insights into compositional details, specifically to distinguish different S sites on the TiS 2 sheets and other S species on the sample. Further, a minimum size is identified (9 S atoms side length), which underlines the importance of moiré reconstructions for stress relief. The TiS 2 sheets coexist with [Au]Ti 1 S 3 clusters, in which a single gold atom is alloyed into the surface and capped by three S atoms. Together with the finding of a critical sheet size, this points toward on-surface Ostwald ripening as a relevant process in the sheet formation. Ab-initio calculations (density functional theory) underscore that the chemical potential of S is an essential descriptor to maintain shape control.

2D nanomaterials↗
DOE OSTI2025

Quantifying precursors to void nucleation and coalescence in aluminum

Ductile rupture is a common failure mode for engineering alloys. It is generally comprised of three mechanisms: void nucleation at secondary particles, void growth, and coalescence of voids. Conventional models for ductile rupture have limited precision for predicting macroscopic failure. This is partially because they have been corroborated using ex-situ observations of these three mechanisms and calibrated by macroscopic strain or stress metrics. In this study, in-situ high-energy X-ray characterization was conducted to correlate sites of void nucleation via particle cracking and sites of void growth with grain-scale metrics. Here it is shown that particle cracking is not predicated by elevated stress metrics, which disagrees with classical models. Instead, particle cracking tended to occur for the largest, least spherical particles. This trend persisted on the aggregate-scale and within individual neighborhoods around particles. Furthermore, an Eshelby analysis illuminated a statistically significant increase in maximum principal stress within a cracked particle, compared to an uncracked particle. In-situ observations also revealed two separate examples of intragranular void growth comprised of flat, crack-like features that grew showing alignment with slip systems of the highest resolved shear stress. Post-mortem fractography revealed a secondary population of dimples on these crack-like features, implying that void sheeting may be occurring during this crack-like void growth. Furthermore, these in-situ observations imply that classical models for void growth, that assume a homogenous medium, should be extended to account for the anisotropic grain-level behavior to correctly capture distinct features of void nucleation and growth.

Al-2219↗
DOE OSTI2026

Manganese Oxidation during Vegetation Burning

Redox recycling of manganese (Mn) plays a key role in organic matter decomposition and nutrient cycling in terrestrial vegetated ecosystems, and it is expected to be changed by fires. This study revealed how Mn is oxidized during vegetation burning, by characterizing the chemical speciation of Mn in fire ash from wildland fires and laboratory burning and evaluating the factors governing its average oxidation state (AOS) and speciation. Manganese in wildland fire ash from different ecosystems showed variable AOS that ranges from 2.5 to 3.3. Laboratory burning experiments showed that Mn oxidation was primarily controlled by fire thermal intensity (temperature × duration) and burning completeness. As heating time increased from 5 min to 5 h at 550 and 700 °C, Mn AOS in the lab-burned vegetation ash increased from 2.7 to 4.0 and the oxidation rate was faster at higher temperature. Diverse Mn species can present in wildland fire ash and differ structurally from biogenic Mn oxides. The oxidized Mn species enable fire ash to mediate oxidative degradation of catechol, demonstrating its potential in mediating organic matter decomposition. This study revealed a new paradigm of Mn redox recycling, as compared to the microbe-mediated Mn redox cycling in the absence of fires.

36 MATERIALS SCIENCE↗
DOE OSTI2026

4D insights into lithium-ion battery sidewall rupture during thermal runaway

Thermal runaway (TR), characterized by rapid exothermic reactions, presents a serious safety risk in lithium-ion batteries (LiBs). External triggers such as high temperatures, mechanical abuse, or internal short circuits (ISCs) can initiate TR, often resulting in sidewall rupture, which may escalate to catastrophic battery pack failure. In this study, we developed and applied high-speed synchrotron imaging techniques to investigate sidewall rupture mechanisms in LiBs subjected to different triggering scenarios. Using in situ 4D tomographic imaging, we visualized the dynamic evolution of sidewall rupture with high spatial and temporal resolution. The results revealed distinct failure behaviors linked to each trigger, underscoring the complex and condition-specific nature of sidewall breach and battery failure. These insights highlight the critical importance of implementing tailored safety strategies across diverse applications. Our findings demonstrate the powerful potential of synchrotron high-speed tomography as a diagnostic tool for advanced safety testing and cell qualification.

25 ENERGY STORAGE↗
DOE OSTI2025

Subventricular Accumulation of Cu in the Aging Mouse Brain Does Not Associate with Anticipated Increases in Markers of Oxidative Stress

Natural aging is associated with mild memory loss and cognitive decline, and age is the greatest risk factor for neurodegenerative diseases, such as Alzheimer’s disease. There is substantial evidence that oxidative stress is a major contributor to both natural aging and neurodegenerative disease, and coincidently, levels of redox active metals such as Fe and Cu are known to be elevated later in life. Recently, a pronounced age-related increase in Cu content has been reported to occur in mice and rats around a vital regulatory brain region, the subventricular zone of lateral ventricles. In our study herein, we have characterized lateral ventricle Cu content in a unique murine model of accelerated aging, senescence accelerated mouse-prone 8 (SAMP8) mice. Our results confirm an age-related increase in ventricle Cu content, consistent with the studies by others in wild-type mice and rats. Specifically, we observed Cu content to increase over the time frame 1 to 5 months and 5 to 9 months, but interestingly, no significant increase occurred between 9 and 12 months (although brain Cu content at 12 months was significantly elevated relative to 1 and 5 month-old animals). Despite the magnitude of Cu increase observed within the cells that comprise the subventricular zone of lateral ventricles (average 3 mM Cu, with isolated subcellular concentrations of 17 mM), we did not detect spectroscopic markers of thiol oxidation, protein aggregation, or lipid oxidation. The lack of evidence for oxidative stress in ex vivo animal tissue is in contrast to in vitro studies demonstrating that thiol, protein, and lipid oxidation is pronounced at these Cu concentrations. We suggest that our findings most likely indicate that the Cu ions in this brain region are sequestered in an unreactive form, possibly extended chains of Cu-thiolate complexes, which do not readily redox cycle in the aqueous cytosol. In conclusion, these results also appear to partially challenge the long-held view that age-related increases in brain metal content drive oxidative stress as we did not observe a concomitant association between age-related Cu increase and markers of oxidative stress, nor did we observe a net increase in Cu content between mice aged 9 and 12 months.

X-ray fluorescence↗
DOE OSTI2025

Calibration and characterization of the line-VISAR diagnostic at the HED-HIBEF instrument at the European XFEL

In dynamic-compression experiments, the line-imaging Velocity Interferometer System for Any Reflector (VISAR) is a well-established diagnostic used to probe the velocity history, including wave profiles derived from dynamically compressed interfaces and wavefronts, depending on material optical properties. Knowledge of the velocity history allows for the determination of the pressure achieved during compression. Such a VISAR analysis is often based on Fourier transform techniques and assumes that the recorded interferograms are free from image distortions. In this paper, we describe the VISAR diagnostic installed at the HED-HIBEF instrument located at the European XFEL along with its calibration and characterization. It comprises a two-color (532, 1064 nm), three-arm (with three velocity sensitivities) line imaging system. We provide a procedure to correct VISAR images for geometric distortions and evaluate the performance of the system using Fourier analysis. We finally discuss the spatial and temporal calibrations of the diagnostic. As an example, we compare the pressure extracted from the VISAR analysis of shock-compressed polyimide and silicon.

47 OTHER INSTRUMENTATION↗
DOE OSTI2025

Biogeochemical Controls on Wood Degradation as a Source of Bioavailable Carbon in Denitrifying Bioreactors

Woodchip bioreactors (WBRs) are important tools for the removal of nitrate in agricultural drainage, but their effectiveness is often limited by the slow degradation of lignocellulosic wood residues into bioavailable forms of carbon that fuel denitrifying microorganisms. Here, we examine biogeochemical factors regulating wood degradation in saturated woodchip beds, with a focus on the effects of dissolved oxygen (DO), iron (Fe), and manganese (Mn) in generating oxidative activity that can enhance wood decomposition. Woodchips from a 10-year-old WBR were characterized with bulk techniques and a novel combination of μX-ray scattering, μXRF, and μXANES to visualize the depletion of crystalline cellulose as a proxy for wood degradation. Woodchips from upstream portions of the reactor exhibited the greatest degradation, probably due to greater DO exposure, and degradation was localized to a 100 to 200 μm thick surface layer that was also associated with higher concentrations of Fe and Mn. Greater degradation was associated with faster nitrate removal. μXANES analysis of Fe and Mn in the surface layer indicated the presence of a microenvironment in which oxygenation reactions of Fe(II) and Mn(II) could contribute to the formation of reactive oxidants involved in the degradation of lignocellulose. In conclusion, our results provide new insight into biogeochemical properties that influence wood decomposition in WBRs at both micro- and macroscales and how these wood degradation processes are coupled with denitrification.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Quantifying the Impact of Metal Population Distribution in MFI-Supported Mo Catalysts for Methane Dehydroaromatization

Precise evaluation of intrinsic kinetic behavior in Mo/MFI catalysts for methane dehydroaromatization (MDA) is confounded by variations in Mo dispersion and speciation, which are influenced by metal loading and zeolite acidity. This work advances the utility of H 2 -temperature programmed reduction (H 2 -TPR) for characterizing Mo/MFI catalysts by enabling quantitative comparison of MoO x populations distinguished by reduction behavior and linked to initial catalytic performance. A comprehensive H 2 reduction pathway is established through systematic H 2 - TPR studies varying catalyst composition (1–10 wt % Mo, Si/Al = 15, 40, ∞), supplemented by UV-Raman spectroscopy, X-ray powder diffraction, N 2 physisorption, NH 3 -TPD, and advanced spectroscopic analysis (in situ XAS with principal component analysis/multivariate curve resolution—alternating least squares). Two low-temperature H 2 -TPR regions capture distinct Mo populations undergoing initial Mo(VI)→Mo(IV) reduction: a lower-temperature population (Mo-RI) associated primarily with highly dispersed, anchored MoO x species expected to predominantly reside within MFI channels, and a higher-temperature population (Mo-RII) corresponding to a broader set of MoO x species that becomes increasingly bulk-like/extrazeolitic at higher Mo loading. Quantification of these populations provides practical, kinetically relevant descriptors for comparing initial MDA rates across catalysts with varying Mo loading, Si/Al ratio, and MoO x heterogeneity. Application of lower-temperature Mo-RI estimates to kinetic measurements reveals a minimum threshold of ∼0.12 × 10 –3 mol Mo-RI/g cat , above which initial forward benzene rates normalized to this population converge despite differences in metal loading and zeolite Brønsted acidity. This threshold coincides with a transition toward a common C 2 -mediated benzene-forming regime, as indicated by approach-to-equilibrium analysis of methane-to-ethane, ethane-to-ethylene, and ethylene-to-benzene reaction steps. Above this threshold, normalized initial benzene rates are nearly invariant with increasing Mo-RII/Mo-RI population ratio, indicating that excess Mo-RII populations, including bulk-like/extrazeolitic MoO x domains present at higher loading, do not measurably suppress benzene formation associated with anchored and mostly channel-confined Mo population under the initial-rate conditions examined.

Mo/MFI↗
DOE OSTI2025

Operando Characterization of Fe in Doped Ni x (Fe 1– x )O y H z Catalysts for Electrochemical Oxygen Evolution

Iron-doped nickel oxyhydroxides, Ni x (Fe 1– x )O y H z , are among the most promising oxygen evolution reaction (OER) electrocatalysts in alkaline environments. Although iron (Fe) significantly enhances the catalytic activity, there is still no clear consensus on whether Fe directly participates in the reaction or merely acts as a promoter. To elucidate the Fe’s role, we performed operando X-ray spectroscopy studies supported by DFT on Ni x (Fe 1– x )O y H z electrocatalysts. We probed the reversible changes in the structure and electronic character of Ni x (Fe 1– x )O y H z as the electrode potential is cycled between the resting (here at 1.10 V RHE ) and operational states (1.66 V RHE ). DFT calculations and XAS simulations on a library of Fe structures in various NiO y H z environments are in favor of a distorted local octahedral Fe(III)O 3 (OH) 3 configuration at the resting state with the NiO y H z scaffold going from α-Ni(OH) 2 to γ-NiOOH as the potential is increased. Under catalytic conditions, EXAFS and HERFD spectra reveal changes in p-d mixing (covalency) relative to the resting state between O/OH ligands and Fe leading to a shift from octahedral to square pyramidal coordination at the Fe site. XES measurements and theoretical simulations further support that the Fe equilibrium structure remains in a formal Fe(III) state under both resting and operational conditions. These spectral changes are attributed to potential dependent structural rearrangements around Fe. The results suggest that ligand dissociation leads to the C 4v symmetry as the most stable intermediate of the Fe during OER. This implies that Fe has a weakly coordinated or easily dissociable ligand that could serve to coordinate the O–O bond formation and, tentatively, play an active role in the Ni x (Fe 1– x )O y H z electrocatalyst.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗