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At least 1,207 records · Page 67
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

From Micro-environments to Macroscopic Effects: How the Alkaline Hydrogen Evolution Reaction Drives Cu Cathodic Corrosion

Cathodic corrosion of copper (Cu) has posed a significant challenge for over a century, impeding various technological progresses such as electrochemical conversion of CO 2 (eCO 2 RR) into fuels and other value-added carbon products. Here, in this study, employing a combined Density Functional Theory (DFT) and kinetic Monte Carlo (kMC) simulation approach, we delve into the atomistic level mechanism driving this phenomenon in Cu. Our hypothesis posits the pivotal role of alkaline hydrogen evolution reaction (HER) in facilitating cathodic corrosion in Cu. We rigorously develop a pH-dependent hydroxide (OH) adsorption mechanism and calculate the equilibrium OH coverage (𝜃 OH ) at varying pH levels, the thermodynamic stability of subsurface oxygen (O sub ), as well as the Cu-vacancy mediated diffusion of subsurface oxygens (O sub ). Through comprehensive analysis, we establish correlation among various microenvironments, including oxygen diffusion in subsurface layers, pH-dependent OH adsorption, and Cu dissolution into the electrolyte as (Cu-OH) complexes. Furthermore, our investigation explores the correlation between surface coordination environment of active sites and cathodic corrosion of Cu. Finally, by integrating DFT-derived thermodynamic data into a kMC model, we successfully predict the formation of experimentally observed corrosion pits on Cu-surfaces. This combined approach not only advances our fundamental understanding of Cu cathodic corrosion but also offers insights crucial for developing effective corrosion mitigation strategies.

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

Boosting the Oxygen Reduction Performance via Tuning the Synergy between Metal Core and Oxide Shell of Metal−Organic Frameworks‐Derived Co@CoO x

Abstract Co core@Co oxide shell (Co@CoO x ) catalysts represent a large family with promising oxygen reduction reaction (ORR) catalytic activity. However, inadequate understanding of Co@CoO x synergy prohibits further pursuit of catalytic performance enhancement. Herein, a Co zeolitic−imidazolate framework was converted into metallic Co, followed by controlled air treatment to form Co@CoO x . The composition and structure evolution as a function of air treatment temperature were studied thoroughly through conventional and synchrotron (both ex‐situ and in‐situ) characterizations, confirming the coexistence of CoO and Co 3 O 4 in the shell. The optimal catalyst showed an ORR half‐wave potential of 0.87 V (vs. RHE) in an alkaline half‐cell and delivered high discharge capacity in an aprotic Li−O 2 battery (7,124 mAh g Cat+C −1 ) and an aqueous Zn−air battery (694 mAh g Zn −1 ) with good performance retention after durability test. Modeling simulation and density functional theory calculation confirmed the charge donation from metal core to oxide shell and shed light on new insights of how metal@metal oxide synergy impacted the ORR via tuning the charge conductivity, oxygen affinity and intermediate transfer pathway. This work opens up a venue to boost ORR catalytic activity from an interfacial synergy perspective.

Wang, Hao↗
NASA NTRS1982

The carbon abundance in the Magellanic Clouds from IUE observations of H II regions

Results are given of observations of the UV spectra of several H II regions in the Magellanic Clouds, with emphasis on obtaining the carbon abundance from the UV lines of C II, C III, and C IV. The observations and results are described, and theoretical model calculations are presented of the H II regions and the relative abundances of H, He, C, N, O, S, Cl, and Ar computed from the UV and visual spectra. In addition, the abundance results for the Magellanic Clouds are compared with the sun, the Orion Nebula, and galactic planetary nebulae. In comparison with solar abundances, carbon is found to be depleted relative to hydrogen in the Magellanic Clouds by an amount larger than that of nitrogen and oxygen in the SMC and by an amount between that of nitrogen and oxygen in the LMC. It is noted that the results are consistent with a scenario that nitrogen and oxygen have greater primary yields in massive stars than carbon, which may be produced predominantly in less massive stars (such that C/N and C/O in galaxies are initially very low and subsequently increase with evolution). Subsequently, the C/N ratio may decrease as secondary production of nitrogen in less massive stars becomes significant.

Dufour, R. J.↗
NASA NTRS1985

High-Temperature Controlled Redox Crystallization Studies

The crystallization of silicates containing redox sensitive ions (e.g., Fe, Ti, Ce) must be performed under controlled and known redox conditions in order to obtain the maximum scientific benefit from experimental study. Furthermore, many compositions crystallize dense phases which settle during ground-based experiments. This settling influences the texture and chemical evolution of the crystallizing system. The purpose of this investigation is to develop a test system in which controlled redox experiments can be performed in the microgravity environment. The system will use solid ceramic oxygen electrolyte cells for control, measurements, and production of the required redox conditions. A preliminary design for a prototype is developed, the electrolyte and furnace tested, and a tentative protocol for experiment developed. The control parameter is to be established and a laboratory prototype built.

Williams, R. J.↗
NASA NTRS1990

Photometry of variable AFGL sources

Results of infrared photometric observations of 63 AFGL sources over the past 9 years are presented. Using these data together with previous measurements of these stars, pulsation periods and mean photometric characteristics are determined. These stars are found to lie midway between optically identified Mira variables and the radio-luminous OH/IR stars in their period distribution and photometric properties. For the sample as a whole, there is no evidence for sudden or transient behavior such as a switch in pulsation mode. Rather, these stars suggest rapid, but continuous, evolution from shorter period Miras with weak mass loss to longer periods and larger mass-loss rates. The carbon-rich stars in the sample have the same period distribution as the oxygen-rich stars. None of the carbon stars have periods as long as those of the very long period radio-luminous OH/IR stars.

Jones, Terry Jay↗
NASA NTRS2000

The Precambrian Biogeochemical Carbon Isotopic Record: Contributions of Thermal Versus Biological Processes

Superplumes offer a new approach for understanding global C cycles. Isotopes help to discern the impacts of geological, environmental and biological processes ujpun the evolution of these cycles. For example, C-13/C-12 values of coeval sedimentary organics and carbonates give global estimates of the fraction of C buried as organics (Forg), which today lies near 0.2. Before Oxygenic photosynthesis arose, our biosphere obtained reducing power for biosynthesis solely from thermal volatiles and rock alteration. Thus Forg was dominated by the mantle redox state, which has remained remarkably constant for greater than Gy. Recent data confirm that the long-term change in Forg had been small, indicating that the mantle redox buffer remains important even today. Oxygenic photosynthesis enabled life to obtain additional reducing power by splitting the water molecule. Accordingly, biological organic production rose above the level constrained by the mantle-derived flux of reduced species. For example, today, chemoautotrophs harvesting energy from hydrothermal emanations can synthesize at most between 0.2 x 10(exp 12) and 2x 10(exp 12) mol C yr-1 of organic C globally. In contrast, global photosynthetic productivity is estimated at 9000 x 10(exp 12) mol C yr-1. Occasionally photosynthetic productivity did contribute to dramatically -elevated Forg values (to 0.4 or more) as evidenced by very high carbonate C-13/C-12. The interplay between biological, tectonic and other environmental factors is illustrated by the mid-Archean to mid-Proterozoic isotopic record. The relatively constant C-13/C-12 values of Archean carbonates support the view that photosynthetically-driven Forg increases were not yet possible. In contrast, major excursions in C-13/C-12, and thus also in Forg, during the early Proterozoic confirmed the global importance of oxygenic photosynthesis by that time. Remarkably, the superplume event at 1.9 Ga did not trigger another major Forg increase, despite the favorable conditions for organic burial that were evidenced by elevated sea levels and higher black shale abundances. Perhaps those superplume-rated processes that favored enhanced organic burial were offset by the ability of mantle-derived redox buffering, which was enhanced during the superplume event, to limit excursions in Forg.

DesMarais, David J.↗
NASA NTRS2005

TRIO: Turbulent Response in Oxygen

This project was designed to build on the results from the successful launch of the Turbulent Oxygen Mixing Experiment (TOMEX) mother-daughter (instrumented and chemical-release) payload (21.126) that was launched in October 2000 from the White Sands Missile Range. The overall science objective was to investigate the evolution of the atmospheric response. at altitudes between 80 and 120 km, to the presence of unstable regions with vertical scales of the order of 1 to 10 km. TRIO was designed to use Na lidar measurements from the MAUUMALT observation on MAUI with a launch of a payload from Pacific Missile Range Facility (PMRF), located on Kauai. During this project, Aerospace participated in a Mission Initiation Conference. put together a science requirements document. performed a site visit to PMRF. prepared a CDR document. and developed a production and calibration procedure for one of the payload instruments. the 3-channel photometer. Unfortunately. NASA decided to terminate the program because of unforeseen (by NASA) range costs. This CDR document represents our view of this project at termination and provides a roadmap to perform this experiment should it be proposed again.

Hecht, J. H.↗
NASA NTRS2009

Solubility of Sulfur in Shergottitic Silicate Melts Up to 0.8 GPA: Implications for S Contents of Shergottites

Shergottites have high S contents (1300 to 4600 ppm; [1]), but it is unclear if they are sulfide saturated or under-saturated. This issue has fundamental implications for determining the long term S budget of the martian surface and atmosphere (from mantle degassing), as well as evolution of the highly siderophile elements (HSE) Au, Pd, Pt, Re, Rh, Ru, Ir, and Os, since concentrations of the latter are controlled by sulfide stability. Resolution of sulfide saturation depends upon temperature, pressure, oxygen fugacity (and FeO), and magma composition [2]. Expressions derived from experimental studies allow prediction of S contents, though so far they are not calibrated for shergottitic liquids [3-5]. We have carried out new experiments designed to test current S saturation models, and then show that existing calibrations are not suitable for high FeO and low Al2O3 compositions characteristic of shergottitic liquids. The new results show that existing models underpredict S contents of sulfide saturated shergottitic liquids by a factor of 2.

Righter, K.↗
DOE OSTI2020

Predictions of the glass transition temperature and viscosity of organic aerosols from volatility distributions

Abstract. Volatility and viscosity are important properties of organic aerosols (OA), affecting aerosol processes such as formation, evolution, and partitioning of OA. Volatility distributions of ambient OA particles have often been measured, while viscosity measurements are scarce. We have previously developed a method to estimate the glass transition temperature (Tg) of an organic compound containing carbon, hydrogen, and oxygen. Based on analysis of over 2400 organic compounds including oxygenated organic compounds, as well as nitrogen- and sulfur-containing organic compounds, we extend this method to include nitrogen- and sulfur-containing compounds based on elemental composition. In addition, parameterizations are developed to predict Tg as a function of volatility and the atomic oxygen-to-carbon ratio based on a negative correlation between Tg and volatility. This prediction method of Tg is applied to ambient observations of volatility distributions at 11 field sites. The predicted Tg values of OA under dry conditions vary mainly from 290 to 339 K and the predicted viscosities are consistent with the results of ambient particle-phase-state measurements in the southeastern US and the Amazonian rain forest. Reducing the uncertainties in measured volatility distributions would improve predictions of viscosity, especially at low relative humidity. We also predict the Tg of OA components identified via positive matrix factorization of aerosol mass spectrometer (AMS) data. The predicted viscosity of oxidized OA is consistent with previously reported viscosity of secondary organic aerosols (SOA) derived from α-pinene, toluene, isoprene epoxydiol (IEPOX), and diesel fuel. Comparison of the predicted viscosity based on the observed volatility distributions with the viscosity simulated by a chemical transport model implies that missing low volatility compounds in a global model can lead to underestimation of OA viscosity at some sites. The relation between volatility and viscosity can be applied in the molecular corridor or volatility basis set approaches to improve OA simulations in chemical transport models by consideration of effects of particle viscosity in OA formation and evolution.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

On the Emergence of Ferromagnetism in LaCoO 3 Ultrathin Films

It is well known that the properties of a crystal evolve as it increases in size from a single atomic plane to that of the bulk. Such size-dependent transitions can stem from many different origins and depend on minute changes to crystal bonding and composition. Here, a model example is that of LaCoO 3 , which is non-magnetic in the bulk but can display ferromagnetism at the nanoscale. Here, the evolution of structure-property relationships is studied in the LaCoO 3-δ /SrTiO 3 (001) system as the thickness of LaCoO 3-δ is increased from a single plane to 10 unit cells. In situ synchrotron X-ray studies are performed during and post-deposition to probe changes in the interactions between structure, stoichiometry, and magnetic behavior. Structural quantification indicates that the oxygen octahedral rotation pattern evolves with thickness, due to inherent differences in crystal symmetry between the film and substrate. The change in rotation modifies the required energy barrier for the spin state transition via the Co–O bond length and Co–O–Co bond angle, affecting the appearance of ferromagnetism. Our results highlight the contributions of high spin Co 2+ and/or high spin Co 3+ to respective weak and robust ferromagnetism and the evolution of properties with size in ultrathin LaCoO 3-δ heterostructures.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Computational analysis of metal–metal bonded dimetal tetrabenzoate redox potentials in the context of ammonia oxidation electrocatalysis

Metal–metal bonded complexes are promising candidates for catalyzing redox transformations. Of particular interest is the oxidation of ammonia to dinitrogen, an important half reaction for the potential utilization of ammonia as a fuel or hydrogen carrier. This work computationally explores 30 different metal–metal bonded dimers (5 different metal centers and 6 different benzoate ligand derivatives) to explore the tunability of the redox potential when ammonia is bound to the complexes as an axial ligand, modeling the first step in ammonia oxidation electrocatalysis. We calculate the redox potentials of these compounds, making reference to experimental data when appropriate, identifying two degrees of tunability: a coarse adjustment, changing the metal center, allows for a wide range of redox potentials to be accessed (from +1.0 to –2.0 V vs. ferrocene/ferrocenium in acetonitrile solution) and a fine adjustment, the para-substituent of the benzoate derivative, which affects the redox potential in a smaller range based on the electron donating/withdrawing effects of the substituent. Ruthenium and osmium tetrabenzoate catalysts are prime candidates for next generation ammonia oxidation catalysts because their redox potentials fall within the direct ammonia fuel cell “viability zone” bracketed by the thermodynamic potentials of oxygen reduction (ORR) and nitrogen reduction (NRR). Rhodium tetrabenzoate species fall above the ORR potential, suggesting ammonia oxidation promoted by Rh 2 catalysts could instead be used to facilitate hydrogen production through coupling to hydrogen evolution at a cathode. The redox potentials of rhenium and iridium tetrabenzoate catalysts fall below the NRR potential suggesting that these compounds could be further investigated in the context of electrochemical ammonia synthesis. Each redox event studied involves electron transfer from the M–M δ* orbital regardless of choice of metal or benzoate ligand derivative; this leads us to believe that the chemical reactivity of the various studied compounds will be similar in the context of ammonia oxidation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1975

A model for the evolution of opaques in mare lavas

The apparent 'reduced' state of the opaque mineral assemblages of mare basalts has led to various hypotheses on their origin through reduction by various media. A model is developed whereby the presence of trivalent titanium (Ti/3+/) and metallic iron in mare lavas at low oxygen fugacities automatically leads to the production of the observed assemblages by cooling near the mare basalt solidus. The 'reduced' assemblages may evolve isochemically at oxygen fugacities near the iron-ilmenite-ferropseudobrookite buffer by a reaction of the form Fe(2+)+2 Ti(3+) = metallic iron +2 Ti(4+).

Haselton, J. D.↗
NASA NTRS2010

Evolution of Regolith Feed Systems for Lunar ISRU 02 Production Plants

The In-Situ Resource Utilization (ISRU) project of the NASA Constellation Program, Exploration Technology Development Program (ETDP) has been engaged in the design and testing of various Lunar ISRU O2 production plant prototypes that can extract chemically bound oxygen from the minerals in the lunar regolith. This work demands that lunar regolith (or simulants) shall be introduced into the O2 production plant from a holding bin or hopper and subsequently expelled from the ISRU O2 production plant for disposal. This sub-system is called the Regolith Feed System (RFS) which exists in a variety of configurations depending on the O2 production plant oxygen being used (e.g. Hydrogen Reduction, Carbothermal, Molten Oxide Electrolysis). Each configuration may use a different technology and in addition it is desirable to have heat recuperation from the spent hot regolith as an integral part of the RFS. This paper addresses the various RFS and heat recuperation technologies and system configurations that have been developed under the NASA ISRU project since 2007. In addition current design solutions and lessons learned from reduced gravity flight testing will be discussed.

Mueller, Robert P.↗
NASA NTRS2018

Almahata Sitta MS-MU-011 and MS-MU-012: Formation Conditions of Two Unusual Rocks From the Ureilite Parent Body

Almahata Sitta meteorites are unique polymict breccia, comprising of many different meteorite groups as individual fragments dominated by ureilite lithologies and are considered to be recovered fragments of the asteroid 2008TC3. Recently, two unusual Almahata Sitta samples (MS-MU-011 and MS-MU-012) have been reported that show close petrogenetic relationships to ureilites. MS-MU-011 is a trachyandesite mainly composed of feldspar (plagioclase and anorthoclase) and pyroxene (pigeonite and augite) having ureilitic oxygen isotopic ratios. MS-MU-012 is the first ureilite example (unbrecciated) containing primary plagioclase crystals. The findings of these two rock types are important to better understand formation conditions of ureilites and the evolution of their parent body(s). In this abstract we discuss formation conditions of these ureilite-related rocks using redox state estimate by Fe valence states of plagioclase and olivine cooling rate calculations.

Mikouchi, T.↗
NASA NTRS1985

Soluble minerals in chemical evolution. I - Adsorption of 5-prime-AMP on CaSO4 - A model system

The adsorption of 5-prime-AMP onto solid CaSO4-2H2O was studied in a saturated suspension as a function of pH and electrolyte concentration. The adsorption is pH-dependent and is directly correlated with the charge on the 5-prime-AMP molecule which is determined by the state of protonation of the N-1 nitrogen of the purine ring and the phosphate oxygens. It is proposed that the binding that occurs between the nucleotide and the salt is electrostatic in nature. The adsorption decreases with increasing ionic strength of the solution which means that in a fluctuating environment of wetting and drying cycles, a biomolecule similar to 5-prime-AMP could be expected to desorb during the drying phase. The results indicate that CaSO4-2H2O can serve as a concentrating surface for biomolecules. The significance of this is discussed with regard to the possible role of soluble minerals and their surfaces in a geochemical model consistent with the evolution of the earth and the origin of life.

Orenberg, J. B.↗
NASA NTRS2006

Nanophase Iron Oxides as an Ultraviolet Sunscreen for Ancient Photosynthetic Microbes: A Possible Link Between Early Organisms, Banded-Iron Formations, and the Oxygenation of the Atmosphere

We propose that nanophase iron oxide-bearing materials provided important niches for ancient photosynthetic microbes on the early Earth that ultimately led to the oxygenation of the Earth s atmosphere and the formation of iron oxide deposits. Atmospheric oxygen and ozone attenuate UV radiation on the Earth today providing substantial protection for photosynthetic organisms. With ultraviolet radiation fluxes likely to have been even higher on the early Earth than today, accessing solar radiation was particularly risky for early organisms. Yet, we know that photosynthesis arose then and played a critical role in subsequent evolution. Of primary importance was protection at approx.250-290 nm, where peak nucleic acid (approx.260 nm) and protein (approx.280 nm) absorptions occur. Nanophase ferric oxide/oxyhydroxide minerals absorb, and thus block, the lethal UV radiation, while transmitting light through much of the visible and near-infrared regions of interest to photosynthesis (400 to 1100 nm). Further, they were available in early environments, and are synthesized by many organisms. Based on ferric oxide/oxyhydroxide spectral properties, likely geologic processes, and the results of experiments with the photosynthetic organisms, Euglena sp. and Chlumydomonus reinhardtii, we propose a scenario where photosynthesis, and ultimately the oxygenation of the atmosphere, depended on the protection of early microbes by nanophase ferric oxides/oxyhydroxides. The results of this study are also applicable to other potentially habitable iron-bearing planetary bodies because of the evolutionary pressure to utilize solar radiation when available as an energy source.

Bishop, Janice L.↗
DOE OSTI2020

Self-grown NiCuO x hybrids on a porous NiCuC substrate as an HER cathode in alkaline solution

Electrocatalysts converted directly from the substrates hold the key to achieve high catalytic activity and durability due to their high bonding strength, intimate electronic contact, and tunable phase composition. Herein, an electrically conductive porous NiCuC substrate was adopted to develop a multi-porous NiCuO x /NiCuC hydrogen evolution reaction (HER) catalyst using a one-step oxidation method in this research. The NiCuO x hybrids were characterized as three typical layers: an outer layer with NiCuO 2 solid solution phase, a partially oxidized intermediate layer, and an inner layer with limited stable oxygen content. Here, the NiCuO x /NiCuC possesses abundant Ni(II)–Cu(II) sites to accelerate the Volmer step via the electrostatic effect with OH – , numerous metallic NiCu sites to facilitate the H adsorption, and highly accessible channels to promote the Heyrovsky step during HER catalysis. As a result, high electrocatalytic performance was obtained with an overpotential of 116 mV at a current density of 10 mA cm –2 in 1.0 M potassium hydroxide, and a stable catalytic performance during the HER process for more than 24 h.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗