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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 1,675 records · Page 93
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Breaking adsorption-energy scaling limitations of electrocatalytic nitrate reduction on intermetallic CuPd nanocubes by machine-learned insights

The electrochemical nitrate reduction reaction (NO 3 RR) to ammonia is an essential step toward restoring the globally disrupted nitrogen cycle. In search of highly efficient electrocatalysts, tailoring catalytic sites with ligand and strain effects in random alloys is a common approach but remains limited due to the ubiquitous energy-scaling relations. With interpretable machine learning, we unravel a mechanism of breaking adsorption-energy scaling relations through the site-specific Pauli repulsion interactions of the metal d-states with adsorbate frontier orbitals. The non-scaling behavior can be realized on (100)-type sites of ordered B2 intermetallics, in which the orbital overlap between the hollow *N and subsurface metal atoms is significant while the bridge-bidentate *NO 3 is not directly affected. Among those intermetallics predicted, we synthesize monodisperse ordered B2 CuPd nanocubes that demonstrate high performance for NO 3 RR to ammonia with a Faradaic efficiency of 92.5% at –0.5 V RHE and a yield rate of 6.25 mol h –1 g –1 at –0.6 V RHE . This study provides machine-learned design rules besides the d-band center metrics, paving the path toward data-driven discovery of catalytic materials beyond linear scaling limitations.

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

Pd-Ru pair on Pt surface for promoting hydrogen oxidation and evolution in alkaline media

Hydrogen oxidation reaction in alkaline media is critical for alkaline fuel cells and electrochemical ammonia compressors. The slow hydrogen oxidation reaction in alkaline electrolytes requires large amounts of scarce and expensive platinum catalysts. While transition metal decoration can enhance Pt catalysts’ activity, it often reduces the electrochemical active surface area, limiting the improvement in Pt mass activity. Here, we enhance Pt catalysts’ activity without losing surface-active sites by using a Pd-Ru pair. Utilizing a mildly catalytic thermal pyrolysis approach, Pd-Ru pairs are decorated on Pt, confirmed by extended X-ray absorption fine structure and high-angle annular dark-field scanning transmission electron microscopy. Density functional theory and ab-initio molecular dynamics simulations indicate preferred Pd and Ru dopant adsorption. The Pd-Ru decorated Pt catalyst exhibits a mass-based exchange current density of 1557 ± 85 A g –1 metal for hydrogen oxidation reaction, demonstrating superior performance in an ammonia compressor.

25 ENERGY STORAGE↗
DOE OSTI2022

Proton spin structure and generalized polarizabilities in the strong quantum chromodynamics regime

The strong interaction is not well understood at low energies or for interactions with low momentum transfer. Chiral perturbation theory gives testable predictions for the nucleonic generalized polarizabilities, which are fundamental quantities describing the nucleon’s response to an external field. We report a measurement of the proton’s generalized spin polarizabilities extracted with a polarized electron beam and a polarized solid ammonia target in the region where chiral perturbation theory is expected to be valid. The investigated structure function g2 characterizes the internal spin structure of the proton. From its moments, we extract the longitudinal–transverse spin polarizability δLT and twist-3 matrix element and polarizability d2¯. Our results provide discriminating power between existing chiral perturbation theory calculations and will help provide a better understanding of this strong quantum chromodynamics regime.

Ruth, D↗
DOE OSTI2017

Geochemical and Microbial Community Attributes in Relation to Hyporheic Zone Geological Facies

The hyporheic zone (HZ) is the active ecotone between the surface stream and groundwater, where exchanges of water, nutrients, and organic matter occur in response to variations in discharge and riverbed properties. Within this region, a confluence of surface-derived organic carbon and subsurface nitrogen (in the form of nitrate) has been shown to stimulate microbial activity and transformations of carbon and nitrogen species. For example, production of gases such as CO 2 , N 2 and N 2 O indicate hyporheic zones might have a significant effect on energy and nutrient flows between the atmosphere and the subsurface. Managed and seasonal river stage changes and geomorphology-controlled sediment texture drive water flow within the HZ of the Columbia River. To examine the relationship between sediment texture, biogeochemistry, and biological activity in the HZ, the grain size distributions for sediment samples taken across 320 m of shoreline were characterized to define geological facies, and the relationships among physical properties of the facies, physicochemical attributes of the local environment, and the structure and activity of associated microbial communities were examined. Mud and sand content and the presence of carbon and nitrogen oxidizers were found to explain the variability in many biogeochemical attributes. Microbial community analysis revealed a high relative abundance of putative ammonia-oxidizing Thaumarchaeota and nitrite-oxidizing Nitrospirae, together comprising ~20% of the total community across all samples, but scant ammonia-oxidizing Bacteria. Network analysis of operational taxonomic units and the measured geophysical, chemical, and functional parameters showed negative relationships between abundance-based modules of organisms and sand and mud contents, and positive relationships with total organic carbon. The relationships identified in this work indicate grain size distribution is a good predictor of biogeochemical properties, and that subsets of the overall microbial community respond to different sediment texture. Some member populations of these sub-communities appear to respond directly to environmental conditions, while others may be dependent on the function of the first group. For example, nitrification is a strong primary response to the observed conditions, and this activity appears to support a larger heterotrophic community. Relationships between facies and hydrobiogeochemical properties enables facies-based conditional simulation/mapping of these properties to inform multiscale modeling of hyporheic exchange and biogeochemical processes.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Comparing DNA, RNA and protein levels for measuring microbial dynamics in soil microcosms amended with nitrogen fertilizer

Abstract To what extent multi-omic techniques could reflect in situ microbial process rates remains unclear, especially for highly diverse habitats like soils. Here, we performed microcosm incubations using sandy soil from an agricultural site in Midwest USA. Microcosms amended with isotopically labeled ammonium and urea to simulate a fertilization event showed nitrification (up to 4.1 ± 0.87 µg N-NO 3 − g −1 dry soil d −1 ) and accumulation of N 2 O after 192 hours of incubation. Nitrification activity (NH 4 + → NH 2 OH → NO → NO 2 - → NO 3 − ) was accompanied by a 6-fold increase in relative expression of the 16S rRNA gene (RNA/DNA) between 10 and 192 hours of incubation for ammonia-oxidizing bacteria Nitrosomonas and Nitrosospira , unlike archaea and comammox bacteria, which showed stable gene expression. A strong relationship between nitrification activity and betaproteobacterial ammonia monooxygenase and nitrite oxidoreductase transcript abundances revealed that mRNA quantitatively reflected measured activity and was generally more sensitive than DNA under these conditions. Although peptides related to housekeeping proteins from nitrite-oxidizing microorganisms were detected, their abundance was not significantly correlated with activity, revealing that meta-proteomics provided only a qualitative assessment of activity. Altogether, these findings underscore the strengths and limitations of multi-omic approaches for assessing diverse microbial communities in soils and provide new insights into nitrification.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Changes in land use driven by urbanization impact nitrogen cycling and the microbial community composition in soils

Transition of populations from rural to urban living causes landscape changes and alters the functionality of soil ecosystems. It is unclear how this urbanization disturbs the microbial ecology of soils and how the disruption influences nitrogen cycling. In this study, microbial communities in turfgrass-grown soils from urban and suburban areas around Xiamen City were compared to microbial communities in the soils from rural farmlands. The potential N 2 O emissions, potential denitrification activity, and abundances of denitrifiers were higher in the rural farmland soils compared with the turfgrass soils. Ammonia oxidizing archaea (AOA) were more abundant than ammonia oxidizing bacteria (AOB) in turfgrass soils. Within turfgrass soils, the potential nitrification activities and AOA abundances were higher in the urban than in the suburban soils. These results indicate a more pivotal role of AOA in nitrification, especially in urban soils. Microbial community composition was distinctly grouped along urbanization categories (urban, suburban, and rural) classified according to the population density, which can in part be attributed to the differences in soil properties. These observed changes could potentially have a broader impact on soil nutrient availability and greenhouse gas emissions.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2014

Electro-Reduction of Nitrogen on Molybdenum Nitride: Structure, Energetics, and Vibrational Spectra from DFT

We used density functional theory to study the electrochemical conversion of nitrogen to ammonia on the (001), (100/010), (101), and (111) surfaces of g-Mo2N. Based on the calculated free energy profiles for the reduction of nitrogen by the associative and dissociative mechanisms, reactivity was found to decrease in the order (111) > (101) > (100/010) E (001). Namely, the cell potentials needed to drive the reduction to ammonia increase in the following order: *0.7 V on (111), *1.2 V on (101), and *1.4 V on (100/010) and (001) surfaces. The (111) surface was found to be the most reactive for nitrogen due to (i) its ability to adsorb the N2 in the side-on position which activates N–N bonding and (ii) its high affinity for N-adatoms which also prevents accumulation of H-adatoms on the catalytic surface at low cell potentials. We have also calculated vibrational frequencies of different NxHy species adsorbed on various g-Mo2N surfaces. The frequencies are found to depend strongly on the type of the binding sites available on the crystal facets. A comparison of the calculated frequencies with the frequencies of the corresponding species in transition metal complexes and other metal surfaces shows that the frequencies of several signature modes fall in a similar region and might be used to assign the spectra of hydrogen and nitrogen containing surface species on different metal surfaces.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2013

Introduction of nitrogen with controllable configuration into graphene via vacancies and edges

Doping with nitrogen in controllable configurations is very valuable to tailor the properties of graphene. Here we report density-functional theory calculations of chemical reactions of ammonia, a widely used nitrogen source, at vacancies and edges of graphene, through which we explore strategies to achieve N-doped graphene with optimized properties. Here, we show that at different defects, ammonia reacts to form nitrogen impurities in distinct configurations, i.e. graphitic-N at single vacancies, pyridinic- or pyrrolic-N at divacancies, pyrrolic-N at armchair edges, and N in a four-member ring at zigzag edges. Moreover, different nitrogen-related defect configurations introduce distinct changes in the electronic structure of graphene. By calculating the core level shift of C 1s electrons, we find configuration-dependent redistribution of electrons around the N-dopant. A discussion of how to achieve optimized doping and enhanced chemical reactivity in experiments is included.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Secondary channels in the thermal decomposition of monomethylhydrazine (CH 3 NHNH 2 )

Mass spectrometric observations in a very low pressure pyrolysis study of the decomposition of the prototypical rocket fuel monomethylhydrazine (MMH) indicated a dominant role for the molecular channels producing NH 3 and H 2 and their coproducts. In contrast, a recent ab initio transition state theory based master equation theoretical study indicated that simple N–N and C–N bond fissions dominate the kinetics. In this work, the possible role of molecular decomposition channels in MMH is explored further through additional investigations of the potential energy surface. These investigations consider the role of triplet channels, of roaming radical channels, and of some previously unexplored pathways for molecular decomposition. New ab initio transition state theory based master equation calculations provide revised predictions for the temperature and pressure dependence of the MMH decomposition kinetics that are in excellent agreement with recent shock tube measurements. These calculations continue to suggest only a very limited contribution from the molecular elimination channels. A roaming pathway is suggested to provide the dominant route for direct formation of ammonia. The possible role of secondary abstraction reactions in the very-low-pressure pyrolysis experiments is briefly discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

The synthesis of ternary acetylides with tellurium: Li 2 TeC 2 and Na 2 TeC 2

The synthesis of ternary acetylides Li 2 TeC 2 and Na 2 TeC 2 is presented as the first example of ternary acetylides with metalloid elements instead of transition metals. The synthesis was carried out by the direct reaction of the corresponding bialkali acetylides with tellurium powder in liquid ammonia. Alternatively, the synthesis of Na 2 TeC 2 was also carried out by the direct reaction of tellurium powder and two equivalents of NaC 2 H in liquid ammonia leading to Na 2 TeC 2 and acetylene gas through an equilibrium containing the assumed NaTeC 2 H molecules besides the reactants and the products. The resulting disordered crystalline materials were characterized by X-ray diffraction and Raman spectroscopy. Implications of these new syntheses on the synthesis of other ternary acetylides with metalloid elements and transition metals are also discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Direct quantitative identification of the “surface trans-effect”

The strong parallels between coordination chemistry and adsorption on metal surfaces, with molecules and ligands forming local bonds to individual atoms within a metal surface, have been established over many years of study. The recently proposed “surface trans-effect” (STE) appears to be a further manifestation of this analogous behaviour, but so far the true nature of the modified molecule–metal surface bonding has been unclear. The STE could play an important role in determining the reactivities of surface-supported metal–organic complexes, influencing the design of systems for future applications. However, the current understanding of this effect is incomplete and lacks reliable structural parameters with which to benchmark theoretical calculations. Using X-ray standing waves, we demonstrate that ligation of ammonia and water to iron phthalocyanine (FePc) on Ag(111) increases the adsorption height of the central Fe atom; dispersion corrected density functional theory calculations accurately model this structural effect. The calculated charge redistribution in the FePc/H 2 O electronic structure induced by adsorption shows an accumulation of charge along the σ-bonding direction between the surface, the Fe atom and the water molecule, similar to the redistribution caused by ammonia. Finally, this apparent σ-donor nature of the observed STE on Ag(111) is shown to involve bonding to the delocalised metal surface electrons rather than local bonding to one or more surface atoms, thus indicating that this is a true surface trans-effect.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Nitrogen electroreduction and hydrogen evolution on cubic molybdenum carbide: a density functional study

We report in this paper a density functional theory study of the nitrogen electroreduction and hydrogen evolution reactions on cubic molybdenum carbide (MoC) in order to investigate the viability of using this material as an electro-catalyst for ammonia synthesis. Free energy diagrams for associative and dissociative Heyrovsky mechanisms showed that nitrogen reduction on cubic MoC(111) can proceed via an associative mechanism and that small negative potentials of -0.3 V vs. standard hydrogen electrode can onset the reduction of nitrogen to ammonia. Kinetic volcano plots for hydrogen evolution showed that the MoC[110] surface is expected to have a high rate for the hydrogen evolution reaction, which could compete with the reduction of nitrogen on cubic MoC. The comparison between the adsorption energies of H-adatoms and N-adatoms also shows that at low potentials adsorption of hydrogen atoms competes with nitrogen adsorption on all the MoC surfaces except the MoC(111) surface. Finally, the hydrogen evolution and accumulation of H-adatoms can be mitigated by introducing carbon vacancies i.e. increasing the ratio of metal to carbon atoms, which will significantly increase the affinity of the catalytic surface for both nitrogen molecules and N-adatoms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Single-atom catalysts templated by metal–organic frameworks for electrochemical nitrogen reduction

The electrocatalytic nitrogen reduction reaction (NRR) offers much prospect for substituting the energy-consuming Haber–Bosch process. Nevertheless, its sluggish reaction kinetics and the competing hydrogen evolution reaction always result in limited ammonia yield and low faradaic efficiency (FE). Here, an Fe-decorated porphyrinic metal–organic framework (MOF) is employed as a precursor to construct single-atom Fe implanted nitrogen-doped carbon catalysts (Fe 1 -N-C) through a mixed ligand strategy. Benefiting from the highly dispersed single-atom Fe sites, hierarchically porous structure and good conductivity, Fe 1 -N-C shows a FE of 4.51% and an ammonia yield rate of 1.56 × 10 -11 mol cm -2 s -1 at -0.05 V versus the reversible hydrogen electrode, superior to those of Co 1 -N-C and Ni 1 -N-C. Theoretical calculations show that Fe 1 -N-C shows the lowest energy barrier of the rate-determining step during the NRR process, consistent with its highest activity obtained in experiments. This work reveals the unique potential of single-atom catalysts for the electrochemical NRR and provides in-depth insights into the catalytic mechanism of the NRR.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Cathodic NH 4 + leaching of nitrogen impurities in CoMo thin-film electrodes in aqueous acidic solutions

Electrocatalytic reduction of dinitrogen (N 2 ) to ammonium (NH 4 + ) in acidic aqueous solutions was investigated at ambient temperature and pressure using a cobalt–molybdenum (CoMo) thin-film electrode prepared by magnetron reactive sputtering. Increased concentrations of ammonium ions (NH 4 + ) were consistently detected in the electrolyte using ion chromatography (IC) after constant-potential electrolysis at various potentials (≤-0.29 V vs. RHE). Using a newly developed analytical method based on ammonia derivatization, performing the experiments with 15 N 2 -labelled gas led however to the detection of increased 14 NH 4 + concentrations instead of 15 NH 4 + . X-ray photoelectron spectroscopic (XPS) analysis of the electrode surface revealed the presence of Mo[triple bond, length as m-dash]N and Mo–NH x species. Several contamination sources were identified that led to substantial increases in the concentration of ammonium ions, including 15 NH 3 impurities in 15 N 2 gas. The observed ammonium concentrations can be consistently ascribed to leaching of nitrogen ( 14 N) impurities incorporated in the CoMo film during the sputtering process. Therefore, researchers in the field are urged to adopt extended protocols to identify and eliminate sources of ammonia contamination and to very carefully monitor the ammonium concentrations in each experimental step.

36 MATERIALS SCIENCE↗
DOE OSTI2023

A General Binary Isotherm Model for Amines Interacting with CO 2 and H 2 O

CO 2 capture by primary or secondary amines has been of great research interests for a century because of its industrial importance. Interest has grown even more, because of the need to eliminate the CO 2 emissions that drive global warming. Experimental evidence shows that CO 2 sorption in primary or secondary amines is accompanied by co-absorption of H 2 O. A quantitative analysis of such CO 2 -H 2 O co-absorption behavior is important for practical process design and theoretical understanding. Even though there is almost an experimental consensus that water enhances CO 2 uptake capacity, an analytic model to explain this phenomenon is not well established. Instead, some empirical models such as the Toth model are used to describe the isotherm without accounting for the presence of water. Recently, we have demonstrated that the isotherm equation of CO 2 sorption into strong-base anion exchange materials with quaternary ammonium can be derived from that of strong-base aqueous alkaline solutions by correcting for the drastic change in water activity and by including an appropriate parameterization of the water activity terms. In this paper, we generalize this model from quaternary ammonium to primary, secondary and tertiary amines either in solutions or as functional groups in polymer resins. For primary, secondary and tertiary amines, the isotherm equation can be derived by extending that of a weak-base aqueous alkaline solution such as aqueous ammonia. The model has been validated using experimental data of aqueous ammonia in literature. Furthermore, this general model even includes quaternary ammonium as a special limit. Hence, this general model offers a platform that can treat the isotherms of solid amines, aqueous amines and aqueous alkaline solutions in a unified way.

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

Waste to worth: a circular solution through lignin engineering

The inefficient management of industrial waste threatens environmental sustainability, requiring scalable resource recovery solutions. To address these challenges, we propose a novel and sustainable in-situ one-step strategy for the simultaneous recovery and functionalization of lignin from industrial black liquor, using a sustainable organic acid system assisted by choline chloride. The functionalized lignin adsorbent material (FLAM) exhibited superior adsorption performance, effectively treating animal feedlot wastewater to recover ammonia. The ammonia enriched FLAM was subsequently repurposed as a slow-release fertilizer, enhancing plant growth and demonstrating a closed-loop pathway for waste valorization and nutrient recycling. Methylene blue was used as a model cationic compound to simulate the adsorption behavior and interactions. FLAM achieved a high adsorption capacity of 725.98 mg/g across a broad pH range, significantly outperforming commercial kraft lignin. This sustainable approach advances circular economy principles by integrating remediation and resource recovery, offering a scalable, eco-friendly solution for environmental applications.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗