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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Carbon mineralization pathways in interfacial adsorbed water nanofilms

Carbon mineralization in humidified carbon dioxide offers a promising route to mitigate anthropogenic emissions in a world stressed by water security. Despite its technological importance, our understanding of carbonation in water-poor environments lags, as traditional dissolution-precipitation pathways struggle to explain the adsorbed water nanofilm-mediated reactivity. Here, we utilize in operando X-ray diffraction (XRD) and advanced molecular simulations to investigate nanoconfined reactions driving forsterite carbonation, the magnesium-rich olivine. By examining magnesium ion dissolution and transport in atomistic simulations of the forsterite-water-carbon dioxide interface and comparing these with the in operando XRD activation energies, we identify both processes as rate-limiting at saturation. Our simulations reveal a mechanistic view of interfacial carbonation, where dissolution and precipitation are mediated by anomalous quasi two-dimensional diffusion. The transport process involves intermittent diffusive hopping in the desorbed state, separated by crawling events that are spatially short but temporally long. This understanding transcends carbon mineralization, with implications for understanding the transport of contaminants in geosystems, the design of multifunctional materials, water desalination, and molecular recognition systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Synthesis pathways to thin films of stable layered nitrides

Controlled synthesis of metastable materials away from equilibrium is of interest in materials chemistry. Thin-film deposition methods with rapid condensation of vapour precursors can readily synthesize metastable phases but often struggle to yield the thermodynamic ground state. Growing thermodynamically stable structures using kinetically limited synthesis methods is important for practical applications in electronics and energy conversion. Here, in this study, we reveal a synthesis pathway to thermodynamically stable, ordered layered ternary nitride materials, and discuss why disordered metastable intermediate phases tend to form. We show that starting from elemental vapour precursors leads to a 3D long-range-disordered MgMoN 2 thin-film metastable intermediate structure, with a layered short-range order that has a low-energy transformation barrier to the layered 2D-like stable structure. This synthesis approach is extended to ScTaN 2 , MgWN 2 and MgTa 2 N 3 , and may lead to the synthesis of other layered nitride thin films with unique semiconducting and quantum properties.

36 MATERIALS SCIENCE↗
DOE OSTI2024

The transformation of lepidocrocite (γ-FeOOH) with Fe($\tiny{II}$) (aq) in slightly acidic media: intermediate pathways and biomimetic behavior

Lepidocrocite (LP) is commonly found in natural or anthropogenic environments and oxidized alloy steel waste storage containers. Despite its importance, the end products formed and its mineral transformation pathways, including intermediate steps and underlying mechanisms under Fe(II) (aq) catalysis still need to be clarified due to decades of dispersed research. Here, in this work, we investigated LP's catalytic transformation with 10 mM and 0.2 mM Fe(II) (aq) at their natural solution pH's via bulk (X-ray Diffraction/XRD, Raman and Attenuated Total Reflectance Fourier Transform Infrared/ATR-FTIR) and micro/nano-scale (semi in situ Transmission Electron Microscopy/TEM) analysis. In general, we observed that goethite (GT) and LP were the main end products. However, a series of two major distinct intermediate events that were initiated by a dissolution type of reaction along with an “induction period” (lack of dissolution) on LP occurred. Fascinatingly, two of the intermediate steps along its mineral transformation presented novel types of non-classical mechanisms of crystallization via some type of guided oriented particle attachment. Furthermore, one of these intermediate steps is biomimetic in appearance, similar to what is observed during bacterial particle attachment. However, it uses inorganic nano-wire antennas that have a sensory-like function as observed with bacterial fimbriae and/or flagellum through an electron transparent film (similar to a bio-film matrix). Finally, this work leads us to comprehend the evolution of some well documented crystal morphologies for GT commonly observed in natural and anthropogenic settings.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Advanced pathways for hydrogen production: a collective view from a technical experts meeting

Hydrogen is an essential fuel and feedstock that can be produced in multiple ways to meet requirements for technological sectors that include energy storage, transportation, petroleum refining, and ammonia synthesis. To consider the future state of hydrogen manufacturing, a team of experts has assembled and examined three emerging hydrogen production technologies – photoelectrochemical, biological, and thermochemical. Each of these emerging technologies holds significant long-term potential for cost reduction while lowering industrial emissions associated with conventional methods of hydrogen manufacture (e.g., steam methane reforming) by using sunlight and renewable resources as primary sources of energy and feedstock, respectively. All three are currently at low technology readiness levels, however their applications, cost reduction opportunities and performance improvement pathways are under active development. In this work, opportunities and outlook for research that can directly advance the technologies are discussed.

08 HYDROGEN↗
DOE OSTI2026

Unravelling chemical pathways of H 2 on Ga 2 O 3 surfaces with spectro-electrochemistry

This work highlights the capability of coupled spectroscopic and electrochemical techniques to probe dynamic surface processes under realistic operating conditions. By simultaneously employing in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and electrochemical impedance spectroscopy (EIS), we elucidate the mechanistic interaction between Ga 2 O 3 and hydrogen under elevated temperatures in a low-oxygen environment. This novel spectro-electrochemical approach allows chemistry to be correlated with the surface charge density of Ga 2 O 3 . Our results reveal a concentration-dependent transition in reaction pathway. At low concentrations, hydrogen reacts with ambient oxygen to form surface hydroxyls. At intermediate concentrations, hydrogen interacts with surface adsorbed oxygen to generate hydroxyl groups along with reducing the surface. Finally, at high H 2 concentrations, hydrogen reduces both hydroxyls and surface oxygen, leading to a highly conductive grain surface. As a result, hydrides form on the reduced Ga 2 O 3 surface. The gained insights are relevant for heterogeneous catalysis and gas sensing.

08 HYDROGEN↗
DOE OSTI2025

Sulfide electrolyte additive enables multi-ionic transfer pathways in alkaline iron redox

Traditional alkaline iron (Fe) batteries rely on the conversion reaction between Fe and Fe(OH) 2 but suffer from hydrogen generation upon Fe formation on charging. Fe 2+ /Fe 3+ redox is a promising anode reaction for alkaline Fe batteries, as it alleviates the formation of hydrogen gas during charging. However, achieving complete Fe 2+ /Fe 3+ redox with a one-electron transfer reaction is challenging due to the formation of electrochemically inert Fe 3 O 4 materials. Here, we demonstrate that an alkaline sulfide-containing electrolyte facilitates the reversible multi-ion transfer and transport pathways within (and beyond) the Fe 2+ /Fe 3+ redox system, including Fe(OH) 2 /Fe 3 O 4 conversion, intercalation of hydrosulfide into layered Fe(OH) 2 , and hydrogen deposition, mediated by hydroxyl ions, hydrosulfide anions, and protons, respectively. This multi-ionic charge storage mechanism delivers a compelling discharge capacity of up to 330 mA h g −1 , as determined by chronopotentiometry measurements at a current density of 0.1 A g −1 , exceeding the theoretical iron redox capacity solely relying on Fe 2+ /Fe 3+ redox (∼299 mA h g −1 ). Our study will highlight the potential of alkaline iron redox as a green anode reaction for various aqueous energy storage systems by utilizing a scalable and low-concentration hydrosulfide electrolyte additive.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Distinct vibrational motions promote disparate excited-state decay pathways in cofacial perylenediimide dimers

A complex interplay of structural, electronic, and vibrational degrees of freedom underpins the fate of molecular excited states. Organic assemblies exhibit a myriad of excited-state decay processes, such as symmetry-breaking charge separation (SB-CS), excimer (EX) formation, singlet fission, and energy transfer. Recent studies of cofacial and slip-stacked perylene-3,4:9,10-bis(dicarboximide) (PDI) multimers demonstrate that slight variations in core substituents and H- or J-type aggregation can determine whether the system follows an SB-CS pathway or an EX one. However, questions regarding the relative importance of structural properties and molecular vibrations in driving the excited-state dynamics remain. Here, we use a combination of two-dimensional electronic spectroscopy, femtosecond stimulated Raman spectroscopy, and quantum chemistry computations to compare the photophysics of two PDI dimers. The dimer with 1,7-bis(pyrrolidin-1′-yl) substituents (5PDI2) undergoes ultrafast SB-CS from a photoexcited mixed state, while the dimer with bis-1,7-(3′,5′-di-t-butylphenoxy) substituents (PPDI2) rapidly forms an EX state. Examination of their quantum beating features reveals that SB-CS in 5PDI2 is driven by the collective vibronic coupling of two or more excited-state vibrations. In contrast, we observe signatures of low-frequency vibrational coherence transfer during EX formation by PPDI2, which aligns with several previous studies. We conclude that key electronic and structural differences between 5PDI2 and PPDI2 determine their markedly different photophysics.

Chemistry↗
DOE OSTI2026

General framework for quantifying dissipation pathways in open quantum systems. III. Off-diagonal subsystem–bath couplings

This paper extends the previously reported theory of dissipation pathways [C. W. Kim and I. Franco, J. Chem. Phys. 160, 214111 (2024)] to incorporate off-diagonal subsystem–bath coupling, which is often required to model molecular systems where the environment directly influences transitions and couplings between subsystem states. We systematically derive master equations for both population transfer and dissipation into individual bath components, for which we also rigorously prove energy conservation and detailed balance. The approach is based on second-order perturbation theory with respect to the subsystem–bath couplings, whose form is not limited to any specific model. The accuracy of the developed method is tested by applying it to diverse model Hamiltonians involving linearly coupled harmonic oscillator baths and comparing the outcomes against the hierarchical equations of motion (HEOM) method. Overall, our method accurately quantifies the contributions of specific bath components to the overall dissipation while significantly reducing the computational cost compared to numerically exact methods such as HEOM, thus offering a path to examine how vibronic interactions steer non-adiabatic processes in realistic chemical systems.

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

Deciphering decomposition pathways of high explosives with cryogenic X-ray Raman spectroscopy

We employed cryogenic X-ray Raman spectroscopy to investigate the early-stage decomposition of the high explosive molecule hexanitrohexaazaisowurtzitane (CL-20). By systematically varying the radiation dose under cryogenic conditions, we induced the decomposition of the molecule using ionizing radiation and observed the evolution of spectral features at the carbon, nitrogen, and oxygen K edges. Through extensive first-principles calculations, we identified key intermediates in the early stages of the decomposition process, resulting from C–C and C–N bond cleavage which leads to the opening of the internal cage structure. A detailed analysis of spectral trends and fingerprints provided evidence supporting N–NO 2 homolytic cleavage as the primary initial decomposition pathway. The combination of advanced core-level spectroscopy methods and state-of-the-art theoretical calculations enabled a comprehensive characterization of the molecular changes induced by controlled radiation dose exposures. In conclusion, our findings establish a benchmark for understanding the decomposition chemistry of high-explosive materials, offering important insights into their stability and reactivity under extreme conditions.

X-ray Raman spectroscopy↗
DOE OSTI2025

Engineering of xylose metabolic pathways in Rhodotorula toruloides for sustainable biomanufacturing

Abstract The oleaginous yeast Rhodotorula toruloides is a promising microbial cell factory for the sustainable production of biofuels and value-added chemicals from renewable carbon sources. Unlike the conventional yeast Saccharomyces cerevisiae, R. toruloides can naturally metabolize xylose, the second most abundant sugar in lignocellulosic hydrolysates. However, its native xylose metabolism is inefficient, characterized by slow xylose uptake and accumulation of D-arabitol. Moreover, despite its phenotype, research on the enzymes involved in xylose metabolism has yet to reach a consensus. Therefore, this review provides a comprehensive analysis of the non-canonical xylose metabolism in R. toruloides, focusing on the properties of key enzymes involved in xylose metabolism. Native xylose reductase and xylitol dehydrogenase exhibit broad substrate promiscuity compared to their counterparts in the xylose-fermenting Scheffersomyces stipitis. Additionally, the absence of xylulokinase expression under xylose-utilizing conditions redirects metabolism toward D-arabitol accumulation. Consequently, D-arabitol dehydrogenases and ribulokinase play essential roles in the xylose metabolism of R. toruloides. These findings highlight the fundamental differences between R. toruloides xylose metabolism and the oxidoreductase pathways observed in other xylose-fermenting yeast, providing insights for metabolic engineering strategies to improve xylose utilization and enhance bioconversion of cellulosic hydrolysates to different bioproducts by R. toruloides.

Biotechnology & Applied Microbiology↗
DOE OSTI2025

Combining Machine Learning and Comparative Effectiveness Methodology to Study Primary Care Pharmacotherapy Pathways for Veterans With Depression

Our objective is to demonstrate an innovative method combining machine learning with comparative effectiveness research techniques and to investigate a hitherto unstudied question about the effectiveness of common prescribing patterns. For Operation Enduring Freedom/Operation Iraqi Freedom veterans with major depressive disorder, we generate pharmacotherapy pathways (of antidepressants) using process mining and machine learning. We select the medication episodes that were started at subtherapeutic doses by the first assigned primary care physician and observe the paths that those medication episodes follow. Using 2-stage least squares, we test the effectiveness of starting at a low dose and staying low for longer versus ramping up fast while balancing observable and unobservable characteristics of patients and providers through instrumental variables. We leverage predetermined provider practice patterns as instruments. We collected outpatient pharmacy data for selective serotonin reuptake inhibitors and selective norepinephrine reuptake inhibitors, patient and provider characteristics (as control variables), and the instruments for our cohort. All data were extracted for the period between 2006 and 2020. There is a statistically significant positive effect (0.68, 95% CI 0.11–1.25) of “ramping up fast” on engagement in care. When we examine the effect of “ramping up slow”, we see an insignificant negative impact on engagement in care (−0.82, 95% CI −1.89 to 0.25). As expected, the probability of drop-out also seems to have a negative effect on engagement in care (−0.39, 95% CI −0.94 to 0.17). We further validate these results by testing with medication possession ratios calculated periodically as an alternative engagement in care metric. Our findings contradict the “Start low, go slow” adage, indicating that ramping up the dose of an antidepressant faster has a significantly positive effect on engagement in care for our population.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2024

Low-dimensional metal–organic frameworks: a pathway to design, explore and tune magnetic structures

Here, the magnetic structure adopted by a material relies on symmetry, the hierarchy of exchange interactions between magnetic ions and local anisotropy. A direct pathway to control the magnetic interactions is to enforce dimensionality within the material, from zero-dimensional isolated magnetic ions, one-dimensional (1D) spin-chains, two-dimensional (2D) layers to three-dimensional (3D) order. Being able to design a material with a specific dimensionality for the phenomena of interest is non-trivial. While many advances have been made in the area of inorganic magnetic materials, organic compounds offer distinct and potentially more fertile ground for material design. In particular magnetic metal–organic frameworks (mMOFs) combine magnetism with non-magnetic property functionality on the organic linkers within the structural framework, which can further be tuned with mild perturbations of pressure and field to induce phase transitions. Here, it is examined how neutron scattering measurements on mMOFs can be used to directly determine the magnetic structure when the magnetic ions are in a 2D layered environment within the wider 3D crystalline framework. The hydrated formate, in deuterated form, Co(DCOO) 2 ·2D 2 O, which was one of the first magnetic MOFs to be investigated with neutron diffraction, is reinvestigated as an exemplar case.

magnetism↗
DOE OSTI2025

The varying temperature- and pressure-induced phase transition pathways in hybrid improper ferroelectric Sr 3 Sn 2 O 7

A variable-temperature and pressure single-crystal diffraction study of hybrid improper ferroelectric Sr 3 Sn 2 O 7 is reported. In combination with symmetry analysis, we reveal that the application of pressure and temperature induce distinct phase transition pathways, driven by a differing response of the octahedral rotations to these stimuli. Contrary to what has been previously predicted, we observe the ferroelectric to paraelectric phase transition between 10.17(18) and 12.13(14) GPa, meaning the hybrid improper ferroelectric phase remains stable to significantly higher pressures than expected.

Ferroelectrics↗
DOE OSTI2024

In vitro evidence that the vasorelaxant effects of 2‐nitro‐1‐phenyl‐1‐propanol on rat coronary arteries involve cyclic nucleotide pathways

Abstract The synthetic nitro‐alcohol 2‐nitro‐1‐phenyl‐1‐propanol (NPP) has endothelium‐independent relaxing properties in isolated preparations of rat aorta and mesenteric artery. In this study, we investigated whether the vasodilator effects occur in coronary vessels and explored whether hyperpolarization is involved in the underlying mechanism of NPP‐induced smooth muscle relaxation. The relaxing responses were studied in isolated preparations of the left anterior descending coronary (ADC) and the septal coronary (SC) arteries, which had been previously maintained under sustained contraction induced by the thromboxane A 2 analogue U‐46619. Administered cumulatively, NPP elicited concentration‐dependent vasorelaxation with similar potency in both vessels. The relaxant effect remained unaffected by the nitric oxide synthase inhibitor L‐NAME, the protein kinase C inhibitor bisindolylmaleimide IV and the Rho‐associated protein kinase inhibitor Y‐27632. However, it was significantly diminished by the adenylyl cyclase inhibitor MDL‐12,330A, the guanylyl cyclase inhibitor ODQ, as well as the K + channel inhibitors tetraethylammonium and CsCl. In ADC preparations impaled with intracellular micropipettes, NPP hyperpolarized the vascular preparation. When the isolated preparation was precontracted by 5‐hydroxytryptamine or 80 mM KCl, NPP‐induced relaxation with lower pharmacological potency compared to the vessels contracted by U‐46619. In conclusion, NPP exhibits vasorelaxant effects on rat coronary arteries, likely involving pathways that include cyclic nucleotide production and membrane hyperpolarization.

Vasconcelos‐Silva, Alfredo Augusto↗
DOE OSTI2025

γ-Aminobutyric acid modulates terpene biosynthesis through the ATG8a-mediated pathway

Terpenes play crucial roles in plant growth, development, and stress responses. The biosynthesis of terpenes is influenced by abiotic stress factors, such as drought, temperature, or light. Here, however, the molecular network underlying how terpenes are regulated in response to environmental stimuli remains largely unknown. Here, we identified the autophagy protein SgATG8a as a key mediator of GABA-regulated terpene production and drought tolerance in Sindora glabra. SgATG8a, evolutionarily related to the animal GABA receptor-associated protein (GABARAP) subfamily, localizes in both the nucleus and cytoplasm. Exogenous GABA treatment not only increased the expression level of terpene synthase genes (SgTPSs) but also led to enhanced accumulation of six main terpene components in Sindora glabra. In addition, GABA alleviated the photosynthesis damage and enhanced leaf biomass under drought conditions. Consistently, overexpression of SgATG8a in Arabidopsis increased terpene synthase gene (SgTPS) expression, leading to the enhanced production of four major terpenes and improved the tolerance of transgenic plants to drought stress by regulating reactive oxygen species (ROS) scavenging systems. Moreover, the transcription factors SgWRKY13 and SgERF4 were identified as interacting partners of SgATG8a, activating SgTPS3 expression. Lectin receptor-like kinase (LecRK1) is involved in the GABA-mediated pathway by interacting with the SgWRKY13/SgERF4-SgATG8a proteins, and the LecRK1-SgWRKY13/SgERF4 phosphorylation module fine-tunes the transcription of the downstream SgTPS3 gene. Taken together, these findings reveal a novel role for GABA in regulating terpene biosynthesis and drought tolerance, providing insights into the molecular mechanism underlying GABA-mediated terpene production.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Plant metacaspases orchestrate wound‐induced pathways for immunity and tissue regeneration

Wounding in plants elicits immunity and tissue repair, but how these responses are coordinated has yet to be elucidated. While plant metacaspases resemble animal caspases in structure and immunity induction, their role in tissue repair and regeneration is unknown. Using Arabidopsis mutants lacking type II metacaspases AtMC4 or AtMC9, we found that the majority of the highly induced, wound-responsive genes in Arabidopsis thaliana are suppressed by the loss of AtMC4, while AtMC9 plays an auxiliary role in defense activation. Specifically, AtMC4, but not AtMC9, is required for the activation of genes involved in tissue repair, such as the developmental regulator WOX5, as well as for root regeneration from excised leaves. Instead, AtMC9 mediates the repression of a subset of basal immunity genes, which modifies the wound-activated defense response from that induced by molecular patterns such as the bacterial flg22 elicitor. Our results thus reveal a conserved protease module that coordinates plant defense and tissue repair upon wounding. They could be new targets to improve crop performance and plant transformation protocols that involve tissue wounding before transgenic plant selection and regeneration. The groups of genes with distinctive requirements for the two metacaspases could provide markers to dissect how these specialized proteases affect different response pathways that underpin the multifaceted wounding response.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Plasmonic pathway to hybrid nanomaterials through energy transfer

Plasmon-induced resonance energy transfer (PIRET) is a promising approach for plasmonic photocatalysis and energy conversion, but challenges include elucidating the mechanism and maximizing its efficiency, both of which are hampered by competing processes. Another challenge is demonstrating that PIRET can photoinitiate reactions that follow efficient pathways compared to bulk processes. We report a plasmon-induced route to plasmonic-polymer hybrid nanomaterials using in operando single-particle spectroelectrochemistry. An energy transfer efficiency of 40% is achievable when the spectral overlap between gold nanorod scattering and polymer absorption is maximized. We also show that PIRET-initiated polymerization proceeds through a different mechanism than bulk polymerization, supported by spectroscopic evidence and density functional theory calculations, highlighting efficient energy cascading from photon to plasmon to exciton and, lastly, to unconventional light-initiated chemistry.

Oh, Hyuncheol [University of Illinois Urbana-Champ↗