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At least 451 records · Page 25

All sources NASA NTRS DOE OSTI

DOE OSTI2022

Promoting the water dissociation of nickel sulfide electrocatalyst through introducing cationic vacancies for accelerated hydrogen evolution kinetics in alkaline media

Developing cost-effective non-precious electrocatalysts with excellent HER performance in alkaline media is of significance for industrial hydrogen production. Herein, we successfully endow Ni 3 S 2 with unprecedentedly enhanced alkaline HER activities by introducing nickel vacancies. The Ni 3 S 2 catalyst with nickel vacancies exhibits an ultralow overpotential of 35 mV at 10 mA cm –2 in 1 M KOH electrolyte, outperforming commercial Pt/C (56 mV) and most reported non-precious electrocatalysts. The electron paramagnetic resonance and X-ray absorption fine structure etc. validates the formation of Ni vacancies and the change of the geometric/electronic structure of Ni 3 S 2 . Additionally, the theoretical calculations reveal that the Ni sites with higher valence state neighbouring the Ni vacancies can promote the water dissociation, playing a vital role in accelerating HER kinetics in alkaline media. Finally, this work may provide a universal strategy to enhance the HER activity of transition-metal compound catalysts in alkaline media by means of cationic defect engineering.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2020

Structural basis for impairment of DNA methylation by the DNMT3A R882H mutation

DNA methyltransferase DNMT3A is essential for establishment of mammalian DNA methylation during development. The R882H DNMT3A is a hotspot mutation in acute myeloid leukemia (AML) causing aberrant DNA methylation. However, how this mutation affects the structure and function of DNMT3A remains unclear. Here we report structural characterization of wild-type and R882H-mutated DNMT3A in complex with DNA substrates with different sequence contexts. A loop from the target recognition domain (TRD loop) recognizes the CpG dinucleotides in a +1 flanking site-dependent manner. The R882H mutation reduces the DNA binding at the homodimeric interface, as well as the molecular link between the homodimeric interface and TRD loop, leading to enhanced dynamics of TRD loop. Consistently, in vitro methylation analyses indicate that the R882H mutation compromises the enzymatic activity, CpG specificity and flanking sequence preference of DNMT3A. Together, this study uncovers multiple defects of DNMT3A caused by the R882H mutation in AML.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2023

Highly active, ultra-low loading single-atom iron catalysts for catalytic transfer hydrogenation

Highly effective and selective noble metal-free catalysts attract significant attention. Here, a single-atom iron catalyst is fabricated by saturated adsorption of trace iron onto zeolitic imidazolate framework-8 (ZIF-8) followed by pyrolysis. Its performance toward catalytic transfer hydrogenation of furfural is comparable to state-of-the-art catalysts and up to four orders higher than other Fe catalysts. Isotopic labeling experiments demonstrate an intermolecular hydride transfer mechanism. First principles simulations, spectroscopic calculations and experiments, and kinetic correlations reveal that the synthesis creates pyrrolic Fe(II)-plN 3 as the active center whose flexibility manifested by being pulled out of the plane, enabled by defects, is crucial for collocating the reagents and allowing the chemistry to proceed. The catalyst catalyzes chemoselectively several substrates and possesses a unique trait whereby the chemistry is hindered for more acidic substrates than the hydrogen donors. This work paves the way toward noble-metal free single-atom catalysts for important chemical reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2020

Hedgehog–FGF signaling axis patterns anterior mesoderm during gastrulation

Significance Anterior–posterior axis patterning is a fascinating but poorly understood developmental process. Single-cell sequencing was utilized to interrogate patterning abnormalities in a mesoderm-specific Hedgehog (Hh) pathway mutant, which revealed selective anterior mesoderm defects. We found that Hh signaling was required for fibroblast growth factor (FGF) pathway activity in nascent mesoderm during gastrulation. Mouse genetics, cell biology, and genomic experiments indicate that FGF signaling acts downstream of Hh signaling in nascent mesoderm for anterior mesoderm morphogenesis. This work demonstrates the utility of applying single-cell technologies to resolve complex developmental phenotypes. Here, it revealed a role for Hh signaling from the node in organizing anterior mesoderm morphogenesis, independent of its role in left–right determination, by promoting FGF signaling in gastrulating mesoderm.

Guzzetta, Alexander↗

DOE OSTI2024

Heterostructural interface engineering for ultrawide-gap nitrides from first principles: Ta C / Al N and Ta C / Ga N rocksalt-wurtzite interfaces

Epitaxial lattice matching is an important condition for the formation of coherent interfaces with low defect densities. However, lattice-matched substrates with the same crystal structure as the active layer are often not available, suggesting opportunities for utilizing heterostructural interfaces. For example, at high Al contents that are interesting for ultrawide-gap applications in power electronics, Al x ⁢Ga 1-x ⁢N semiconductor alloys in the (0001) orientation of the wurtzite (wz) structure become lattice-matched to (111)-oriented rocksalt (rs) Ta⁢C substrates. To predict the expected interface atomic structures under different synthesis conditions, we perform high-throughput density-functional-theory calculations, using an algorithm for systematic sampling of the possible stacking sequences of the atomic layers on the in-plane hexagonal lattice. The approach considers octahedral, tetrahedral, and prismatic coordination motifs, and is generally applicable for the modeling of commensurate rs/wz heterostructural interfaces. Our results provide guidance for synthesis control of substrate-film bonding and the polarity of ultrawide-gap Al x⁢ Ga 1-x⁢ N alloys on Ta⁢C substrates.

36 MATERIALS SCIENCE↗

NASA NTRS1980

Ion-implanted laser annealed silicon solar cells

Development of low cost solar cells fabrication technology is being sponsored by NASA JPL as part of the Low Cost Solar Array Project (LSA). In conformance to Project requirements ion implantation and laser annealing were evaluated as junction formation techniques offering low cost-high throughput potential. Properties of cells fabricated utilizing this technology were analyzed by electrical, transmission electron microscopy, Rutherford backscattering and secondary ion mass spectrometry techniques. Tests indicated the laser annealed substrates to be damage free and electrically active. Similar analysis of ion implanted furnace annealed substrates revealed the presence of residual defects in the form of dislocation lines and loops with substantial impurity redistribution evident for some anneal temperature/time regimes. Fabricated laser annealed cells exhibited improved spectral response and conversion efficiency in comparison to furnace annealed cells. An economic projection for LSA indicates a potential for considerable savings from laser annealing technology.

Katzeff, J. S.↗

DOE OSTI2022

Tritium diffusion and formation in the bulk and defective surface of γ-LiAlO2 pellets: First-principles investigation

In tritium-producing burnable absorber rods (TPBAR), γ-LiAlO2 is used in the form of an annular ceramic pellet enriched with the 6Li isotope. When irradiated in a pressurized water reactor (PWR), the 6Li pellets absorb neutrons and produce tritium (3H) through 6Li + n 3H + α. The 3H chemically reacts with the metal getter where it is captured and leads to formation of a metal hydride. For TPBARs to enable effective tritium production in PWRs, we investigated the 3H diffusion pathways in the bulk and surface of γ-LiAlO2 with different concentrations of lithium defects. The calculated results for bulk and low-index surfaces, thermal conductivity, 3H activation energy barriers, and the 3H diffusion coefficients in γ-LiAlO2 are in good agreement with the available experimental values. In the bulk, our results show that the smallest activation energy barrier is 0.63 eV for substitutional 3H diffusion with a diffusion coefficient of 3.25x10-12 m2/s. After 3H diffused from bulk to the surface, it could form different species (such as 3H2, 3H2O, C3H4) depending on the surface structure, vacancy types and the impurity carbon. Our results indicate that the 3H2 is the main product from γ-LiAlO2 pellets. As the number of VLi vacancies and 3H atoms increases under irradiation (3H-rich condition), 3H2O release could increase from the surface of γ-LiAlO2 pellets.

Jia, Ting↗

DOE OSTI2025

Morphology, Deformations, and Photocatalytic Activity of Thermally Treated Brookite Titanium Dioxide Thin Films

Metastable states, in which the coupling between long-range lattice deformations and electronic properties can be controlled, provide a pathway to tailoring the behavior of photocatalytic materials by directing the flow of photoinduced charge carriers. Brookite is a metastable polymorph of earth-abundant TiO 2 that exhibits photocatalytic function and, due to its high energy relative to the anatase and rutile polymorphs, may serve as a precursor for the formation of transitional metastable structures. In this work, facile thermal annealing is employed to promote the formation of predominantly brookite-phase films, regulate the brookite lattice distortions, and determine the effect of these distortions on charge separation, ultimately directed at enhancing photocatalytic activity. Profile fitting of X-ray diffraction patterns and peak shifts in Raman spectra revealed structural distortions of the brookite lattice. Structural defects, including lattice gliding, dislocations, stacking faults, and twin boundaries, were observed using scanning transmission electron microscopy. First-principles simulations reveal how the lattice distortions associated with stacking faults induce band bending, thus increasing the photocatalytic activity of brookite. In conclusion, this study provides insight into the microstructural tuning of metastable phases to enhance their unique functionalities.

band bending↗

DOE OSTI2025

In Situ Electrochemistry of Buried Interfaces in Metal Halide Perovskites: Probing Energy Bands, Halide Redox Activity, and Kinetics

Control over charge injection and extraction processes across buried interfaces is fundamental for all (opto)electronic multilayer device platforms, necessitating detailed understanding of local structural and chemical differences that promote defect formation, distort energetic band-edge alignments, and alter charge transport processes. Herein, the implementation of a low-cost electroanalytical methodologies’ tool suite is described to quantitatively characterize buried interfaces and redox reactions in printable, mixed electrical–ionic, and redox-active metal halide perovskites and a prototypical hole-transporting nickel oxide (NiO x ) thin film. The objective is to demonstrate the power of electrochemical methodologies to improve the nanoscale understanding of complex interfaces within optoelectronic devices by providing case studies on how to: i) differentiate between electronic and chemical properties in NiO x contacts; ii) measure changes in reversibility of halide redox reactions via NiO x surface states; iii) assess energy alignment and charge transport across (modified) buried interfaces; and iv) quantify defects at buried interfaces that change with modifiers and differences in perovskite processing, including increasing defect concentrations when films are slot-die-coated versus spin-cast. The collective approach addresses major challenges in understanding the precise energy landscape and interface reactivity under relevant electric fields that mimic operando conditions (away from equilibrium) and across length scales in thin film device formats.

(spectro)electrochemistry↗

DOE OSTI2024

Elucidation of Ce/Zr ratio effects on the physical properties and catalytic performance of CuO x /Ce y Zr 1− y O 2 catalysts

Although cerium oxide (CeO 2 ) is widely used as a catalyst support, its limited defect sites and surface oxygen vacancy/mobility should be improved. The incorporation of zirconium (Zr) in the cerium (Ce) lattice is shown to increase the number of oxygen vacancies and improve catalytic activity. Using a fixed surface density (SD) of copper (∼2.3 Cu atoms per nm 2 ) as a surface species, the role of the support (Ce y Zr 1−y O 2 (y = 1.0, 0.9, 0.6, 0.5, and 0.0)) and defect site effects in the CO oxidation reaction was investigated. Spectroscopic (e.g., Raman, XRD, XPS) and microscopic (e.g., SEM-EDX, HR-TEM) characterization techniques were applied to evaluate the defect sites, crystallite size, lattice parameters, chemical composition, oxidation states of elements and microstructure of the catalysts. Here, the CO oxidation reaction with varied CO : O 2 ratios (1 : 5, 1 : 1, and 1 : 0.5 (stoichiometric)) was used as a model reaction to describe the relationship between the structure and the catalytic performance of each catalyst. Based on the characterization results of Ce y Zr 1−y O 2 materials, the addition of Zr causes physical and chemical changes to the overall material. The inclusion of Zr into the structure of CeO 2 decreased the overall lattice parameter of the catalyst and increased the number of defect sites. The prepared catalysts were able to reach complete CO conversion (∼100%) at low temperature conditions (<200 °C), each showing varied reaction activity. The difference in CO oxidation activity was then analyzed and related to the structure, wherein Cu loading, surface oxygen vacancies, reduction–oxidation ability, CuO x –support interaction and oxygen mobility in the catalyst were the crucial descriptors.

36 MATERIALS SCIENCE↗

DOE OSTI2025

The C2 domain augments Ras GTPase-activating protein catalytic activity

Regulation of Ras GTPases by GTPase-activating proteins (GAPs) is essential for their normal signaling. Nine of the ten GAPs for Ras contain a C2 domain immediately proximal to their canonical GAP domain, and in RasGAP (p120GAP, p120RasGAP;RASA1) mutation of this domain is associated with vascular malformations in humans. Here, we show that the C2 domain of RasGAP is required for full catalytic activity toward Ras. Analyses of the RasGAP C2-GAP crystal structure, AlphaFold models, and sequence conservation reveal direct C2 domain interaction with the Ras allosteric lobe. This is achieved by an evolutionarily conserved surface centered around RasGAP residue R707, point mutation of which impairs the catalytic advantage conferred by the C2 domain in vitro. In mice,R707Cmutation phenocopies the vascular and signaling defects resulting from constitutive disruption of theRASA1gene. In SynGAP, mutation of the equivalent conserved C2 domain surface impairs catalytic activity. Our results indicate that the C2 domain is required to achieve full catalytic activity of GAPs for Ras.

Science & Technology - Other Topics↗

DOE OSTI2020

Hierarchical Defect Engineering for LiCoO 2 through Low-Solubility Trace Element Doping

Real-world industry-relevant battery composite electrodes are hierarchically structured. Their structural and chemical complexity is featured by ubiquitous multi-scale porosity and cracks, solid-solid and solid-liquid interfaces, compositional and redox heterogeneity, as well as lattice disordering and deformation. In particular for the active cathode particles, which are the fundamental building blocks for the energy reservoir, it is a consensus that these structural and chemical defects could have a profound impact on the battery performance. An in-depth understanding of the underlying mechanisms could critically inform the cathode material engineering, which would have a tremendous potential but remains a daunting challenge at present. In this work, we tackle this question by studying LiCoO 2 (LCO) with trace doping of Ti, which exhibits a low solubility in the LCO layered lattice. Additionally, we observed the spontaneous and heterogeneous segregation of the dopant (Ti) across a wide range of length scales. In addition to the modification of the particle surface and the buried grain boundaries within the particle, we reveal that the Ti doping has induced a significant amount of lattice distortions, which, in turn, promotes the robustness of the LCO lattice at high state of charge (above 4.5V). Our result formulates a multi-scale defect engineering strategy that could be applicable to the synthesis of a broad range of energy materials for applications in batteries and beyond.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Estimates of Quantum Tunneling Effects for Hydrogen Diffusion in PuO 2

We detail the estimation of activation energies and quantum nuclear vibrational tunneling effects for hydrogen diffusion in PuO 2 based on Density Functional Theory calculations and a quantum double well approximation. We find that results are relatively insensitive to choice of exchange correlation functional. In addition, the representation of spin in the system and use of an extended Hubbard U correction has only a small effect on hydrogen point defect formation energies when the PuO 2 lattice is held fixed at the experimental density. We then compute approximate activation energies for transitions between hydrogen interstitial sites seeded by a semi-empirical quantum model and determine the quantum tunneling enhancement relative to classical kinetic rates. Our model indicates that diffusion rates in H/PuO 2 systems could be enhanced by more than one order of magnitude at ambient conditions and that these effects persist at high temperature. The method we propose here can be used as a fast screening tool for assessing possible quantum nuclear vibrational effects in any number of condensed phase materials and surfaces, where hydrogen hopping tends to follow well defined minimum energy pathways.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

Lifelong cytomegalovirus and early‐LIFE irradiation synergistically potentiate age‐related defects in response to vaccination and infection

Abstract While whole‐body irradiation (WBI) can induce some hallmarks of immune aging, (re)activation of persistent microbial infection also occurs following WBI and may contribute to immune effects of WBI over the lifespan. To test this hypothesis in a model relevant to human immune aging, we examined separate and joint effects of lifelong latent murine cytomegalovirus (MCMV) and of early‐life WBI over the course of the lifespan. In late life, we then measured the response to a West Nile virus (WNV) live attenuated vaccine, and lethal WNV challenge subsequent to vaccination. We recently published that a single dose of non‐lethal WBI in youth, on its own, was not sufficient to accelerate aging of the murine immune system, despite widespread DNA damage and repopulation stress in hematopoietic cells. However, 4Gy sub‐lethal WBI caused manifest reactivation of MCMV. Following vaccination and challenge with WNV in the old age, MCMV‐infected animals experiencing 4Gy, but not lower, dose of sub‐lethal WBI in youth had reduced survival. By contrast, old irradiated mice lacking MCMV and MCMV‐infected, but not irradiated, mice were both protected to the same high level as the old non‐irradiated, uninfected controls. Analysis of the quality and quantity of anti‐WNV immunity showed that higher mortality in MCMV‐positive WBI mice correlated with increased levels of MCMV‐specific immune activation during WNV challenge. Moreover, we demonstrate that infection, including that by WNV, led to MCMV reactivation. Our data suggest that MCMV reactivation may be an important determinant of increased late‐life mortality following early‐life irradiation and late‐life acute infection.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2021

Excited States of Crystalline Point Defects with Multireference Density Matrix Embedding Theory

Accurate and affordable methods to characterize the electronic structure of solids are important for targeted materials design. Embedding-based methods provide an appealing balance in the trade-off between cost and accuracy-particularly when studying localized phenomena. Here, we use the density matrix embedding theory (DMET) algorithm to study the electronic excitations in solid-state defects with a restricted open-shell Hartree-Fock (ROHF) bath and multireference impurity solvers, specifically, complete active space self-consistent field (CASSCF) and n-electron valence state second-order perturbation theory (NEVPT2). In this work, we apply the method to investigate the electronic excitations in an oxygen vacancy (OV) on a MgO(100) surface and find absolute deviations within 0.05 eV between DMET using the CASSCF/NEVPT2 solver, denoted as CAS-DMET/NEVPT2-DMET, and the nonembedded CASSCF/NEVPT2 approach. Next, we establish the practicality of DMET by extending it to larger supercells for the OV defect and a neutral silicon vacancy in diamond where the use of nonembedded CASSCF/NEVPT2 is extremely expensive.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Active Learning Surrogates for Integrating Electron Microscopy and Computational Insights from Simulations in Autonomous Experiments

Artificial Intelligence (AI) combined with simulations and experiments has great potential to accelerate scientific discovery across technology and pharmaceuticals. However, the gap between simulations and experiments is challenging due to disparities in time and scale, making it difficult to estimate properties like energy and electronic states from experiments, and to provide feedback based on theoretical insights.Our research addresses the challenge by developing unique deep kernel based surrogate models that learns from microscopic images, mapping structural features to energy differences from defect formation. We start with full-training using simulated images to determine optimal settings, establishing a baseline for active learning. Using these settings from the baseline, active learning is trained, and predicts structures along simulation trajectories based on uncertainty and energetic stability, thus reducing data requirements, simulation time and computational costs. The results demonstrate that the model achieves a low average error margin of approximately 0.03 meV, indicating good performance. To enhance feature extraction and reconstruction capabilities, we developed an autoencoder-decoder as additional surrogate to create latent space to capture essential features, enabling precise comparisons between simulations and experiments. The results from this model achieved a reconstruction loss of around 0.2 and accurately reconstructed molecular structures.Overall, this work advances the steering of experiments through computational simulations by employing a surrogate models that actively predicts the trajectories of structural evolution, achieving time-to-solution comparable to experimental measurements.

Saranathan, Gayathri [Hewlett-Packard]↗

NASA NTRSDate not supplied

Stress-Activated Positive Holes (O− in a Matrix of O2–) Cause DNA Damage in Surface-Dwelling Organisms: Unveiling Mutation-Induced Secrets of Nature

Peroxy defects consist of pairs of tightly bonded oxygen anions in the –1 valence state such as in O3X/OO\YO3 with X, Y = Si4+, Al3+ etc. They commonly occur in igneous, metamorphic and many sedimentary rocks. When such rocks are stressed by tectonic forces, peroxy defects break up, releasing highly mobile electronic charge carriers: defect electrons in the O2– sublattice, i.e. unbound O–, known as “positive holes”, h•. The h• can flow out of stressed rock volumes, spreading far and wide, causing electric currents and electrochemical reactions. This study explores how the h• impact the electron flow in the electron transport chain (ETC) of organisms on the surface of rocks such as gabbro and granite. We found that, by forming hydroxyl radicals and superoxide anions, the h• disrupt the in vivo coordination of reduction-oxidation reactions that are essential for the timing of the redox cycle. Our observations show that stress activation of h• delays the sprouting of certain plant seeds and impedes the growth of yeast cultures, Saccharomyces cerevisiae. The h• induce mutations and affect plant development as evidenced by reduced stem length and leaf size. At the same time, the h• serve as a source of abiotic oxidation, capable of forming various organic compounds in situ. Through the generation of radical species that create new carbon-carbon bonds the h• facilitate the abiotic synthesis of hydrocarbons and other organic molecules essential to life, including porphyrins. Our findings highlight the intricate interplay between positive holes, redox timing, and biological processes, revealing their significant role in influencing the growth and development of organisms in tectonically stressed crustal environments. Understanding these effects enhances our broader comprehension of redox biology and the influence of environmental factors on cellular development in natural settings.

astrobiology↗

DOE OSTI2020

Detailed Characterization of an Annealed Reduced Graphene Oxide Catalyst for Selective Peroxide Formation Activity

Recently, electrochemical hydrogen peroxide (H 2 O 2 ) generation from oxygen molecules has been extensively studied. Thus far, the best peroxide activity under alkaline conditions has been reported at the surface of a mild reduced graphene oxide annealed at 600 °C (mrGO-600). However, the detailed material information, such as chemical functionality and structural morphology, is unknown, which results in ambiguous debates on its catalytic active sites. Therefore, to solve this problem, we intensively characterize the structure of mrGO-600 to clarify the origin of its catalytic activity. Various characterizations, including X-ray photoelectron spectroscopy, Raman spectroscopy, infrared spectroscopy, near-edge X-ray absorption fine spectroscopy, and high-resolution transmittance electron microscopy coupled with in situ infrared spectroelecrochemistry, reveal that the annealing process generates not only various hole edge defects that are related to the ring ether group but also numerous point defects that result in a small-sized disconnected graphitic carbon region. These defects are believed to form a unique atomic level configuration in mrGO-600, which enables it to facilitate high peroxide-generated activity from oxygen molecules in an alkaline electrolyte.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗