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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Graphene-supported single atom catalysts for high performance lithium-oxygen batteries

The optimal choice of d-block metals in single atom catalysts (SACs) is crucial for designing efficient electrocatalysts for activating the Oxygen reduction reaction (ORR)/ Oxygen evolution reaction (OER) in lithiumoxygen batteries (LOBs). Herein, we used the Quantum Mechanics methods to understand the origin of reactivity for a series of 16 d-block metals supported on nitrogen-doped graphene as SACs for ORR and OER in LOBs. Based on the Gibbs free energy calculations, we found that among the 16 SACs investigated, Zn-SAC exhibits the highest electrochemical activity with the lowest overpotential of 0.17 V. Here we then used machine learning (ML) to develop an intrinsic descriptor, phi, that correlates the catalytic activity with electronic and chemical properties of the catalytic centers at the M-N 4 active site on graphene surface. We established a linear relationship between phi and the catalytic activity that provides guidance for designing efficient SACs for electrocatalysis in LOBs. To validate these predictions, we report electrochemical measurements showing that Zn-SAC exhibits an ultra-stable cyclability with reduced overpotentials over Mo-SAC and nitrogen-doped graphene (NG), confirming our theoretical prediction. This fundamental work provides a deep understanding on the rational design of efficient SACs for OER/ ORR in LOBs.

25 ENERGY STORAGE↗
DOE OSTI2021

Iridium metallene oxide for acidic oxygen evolution catalysis

Exploring new materials is essential in the field of material science. Especially, searching for optimal materials with utmost atomic utilization, ideal activities and desirable stability for catalytic applications requires smart design of materials’ structures. Herein, we report iridium metallene oxide: 1 T phase-iridium dioxide (IrO 2 ) by a synthetic strategy combining mechanochemistry and thermal treatment in a strong alkaline medium. This material demonstrates high activity for oxygen evolution reaction with a low overpotential of 197 millivolt in acidic electrolyte at 10 milliamperes per geometric square centimeter (mA cm geo –2 ). Together, it achieves high turnover frequencies of 4.2 s UPD –1 (3.0 s BET –1 ) at 1.50 V vs. reversible hydrogen electrode. Furthermore, 1T-IrO 2 also shows little degradation after 126 hours chronopotentiometry measurement under the high current density of 250 mA cm geo –2 in proton exchange membrane device. Theoretical calculations reveal that the active site of Ir in 1T-IrO 2 provides an optimal free energy uphill in *OH formation, leading to the enhanced performance. The discovery of this 1T-metallene oxide material will provide new opportunities for catalysis and other applications.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Ambient pressure X-ray photoelectron spectroscopy study of room-temperature oxygen adsorption on Cu(1 0 0) and Cu(1 1 1)

We investigated the room-temperature chemisorption of oxygen on Cu(1 0 0) and Cu(1 1 1) using ambient-pressure X-ray photoelectron spectroscopy (APXPS). A shoulder-to-shoulder comparison between the oxygen-gas titration on the two surfaces reveals that Cu(1 0 0) is the more active for oxygen dissociative chemisorption when the surfaces are clean. The (2 $\sqrt{2}$ × $\sqrt{2}$)R45o missing-row reconstruction appears in Cu(1 0 0)’s LEED image after about 10 4 Langmuir of oxygen exposure, whereas on Cu(1 1 1), no long-range ordering was observed throughout the whole experiment. An oxide layer consisting of cuprous and cupric oxide shows up on Cu(1 1 1) at an oxygen exposure that is significantly lower than for Cu(1 0 0). This observation suggests that the presence of (2 $\sqrt{2}$ × $\sqrt{2}$)R45o missing-row reconstruction layer slows down Cu(1 0 0) oxidation. Literature has widely reported that surface morphology influences the copper oxidation process. This study provides an XPS demonstration that copper surface oxide formation in O 2 at room temperature depends on the surface crystallographic orientation.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Oxidation of Silicon Carbide with Atomic Oxygen through the Passive-to-Active Transition

The inelastic and reactive scattering dynamics of O( 3 P) atoms on a 6H-silicon carbide (SiC) surface were investigated as a function of temperature with a molecular beam-surface scattering technique that employed a rotatable mass spectrometer detector. One set of experiments used a pulsed hyperthermal beam that produced ~8 km s –1 O atoms, and another set of experiments used a continuous beam that contained O atoms with a nominal velocity of ~2 km s –1 . When exposed to the relatively low-flux, pulsed hyperthermal O-atom beam, a passive oxide layer on the SiC that formed at lower temperatures decomposed as the temperature increased above 1673 K. Instead of entering an active oxidation regime, a graphitic layer formed on the surface and largely protected the underlying SiC from incoming O atoms. Investigation of the oxide decomposition without O-atom bombardment revealed volatile Si and SiO products at the moment that the oxide decomposed, implying that Si sublimation occurs concurrently with oxide decomposition. In the experiment with the continuous (higher flux) O-atom beam, volatile SiO and CO products were observed after the passive oxide decomposed, indicating that active oxidation was reached. Finally, the results of this study provide evidence for the importance of Si sublimation within the active oxidation regime. Above the passive-to-active transition temperature, Si sublimation is an ongoing process, and continuous active oxidation will only occur if sufficient oxygen reacts with the surface to produce SiO more quickly than a graphitic layer can form. Thus, accurate models of SiC ablation by atomic oxygen must account for multiple competing mechanisms that depend on the surface temperature and incident O-atom flux.

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

Performance enhancement and degradation mechanism identification of a single-atom Co–N–C catalyst for proton exchange membrane fuel cells

Development of platinum group metal (PGM)-free catalysts for oxygen reduction reaction (ORR) has been a strategic research topic for proton exchange membrane (PEM) fuel cells. Present state-of-art PGM-free ORR catalysts are Fe, N co-doped carbon (Fe-N-C) catalysts, which unfortunately exhibit instability concerns. Herein, we report a stable atomically dispersed Co, N co-doped carbon (Co-N-C) catalyst with high Co content of 1.0 at% and the active site, i.e., the coordination of Co, is CoN2+2 in nature. The Co-N-C catalyst demonstrated high ORR activity comparable to, and high stability over 3 times better than, that of the Fe-N-C catalyst. It also achieved a high activity of 22 mA cm2 at 0.9 ViR-free and a power density of 0.61 W cm-2 under 1.0 bar H2/O2. Further, we identify two main degradation mechanisms of the PGM-free catalysts: catalyst oxidation by H2O2/radicals and demetalation. The improved stability of Co-N-C relative to Fe-N-C is attributed to less Fenton-reactive nature of Co and significantly enhanced resistance to demetalation of Co-N-C.

Xie, Xiaohong↗
NASA NTRS1997

A Survey of Large-Scale Variations in Thermospheric Oxygen Column Density with Magnetic Activity as Inferred from Observations of the FUV Dayglow

Brightness of the terrestrial far-ultraviolet (FUV) dayglow is dominated by the 130.4-nm emission of neutral atomic oxygen, OI, and variations in the brightness observed from altitudes high above the emitting region reflect variations in thermospheric oxygen density. This paper summarizes the results of an initial survey of the Dynamics Explorer 1 observations of the FUV dayglow through a presentation of 13 representative events selected to demonstrate the spatial extent and short-term temporal stability of the brightness perturbations. The emphasis here is on the morning sector of local time and the polar cap for observations obtained in the time interval from September 23, 1981, through January 19, 1982. An analytic expression is derived for the average response of the FUV photometer to the dayglow during periods of high-latitude magnetic quiescence. The remaining observations in this time interval are then analyzed for their deviations from the established quiet time values. Deviations of -40% to +30% are found following intervals of increased magnetic activity. The most significant decreases (-30% to -40%) are observed equatorward of the instantaneous aurora] oval only after sustained periods (approx. 6 hours) of intense magnetic activity (average AE greater than approx. 700 nT). Decreases extend equatorward from the aurora to geographic latitudes as low as approx. 30 deg N. Decreases of lesser magnitude that do not extend as far equatorward are associated with sustained periods of more moderate activity in which the average value of AE is smaller (approx. 300-400 nT). Also, the spatial extent and magnitude of the decreases in the morning sector appear greater when the IMF B(sub y) component is positive. In both cases, decreases are readily observed within the polar cap. Localized enhancements of +20% to +30% occur much less frequently and are detected at the middle latitudes, well equator-ward of the auroral oval.

Nicholas, A. C.↗
DOE OSTI2022

Mechanistic insights into metal, nitrogen doped carbon catalysts for oxygen reduction: progress in computational modeling

We report metal and nitrogen doped carbon materials (denoted as M–N–C) synthesized through high-temperature pyrolysis have been found to exhibit activity for oxygen reduction reaction (ORR) approaching that of Pt and electrochemical stability higher than previous MN 4 -containing macrocyclic molecular catalysts. Tremendous efforts have thus been devoted to the advancement of M–N–C catalysts as an economical alternative to Pt-based catalysts for proton exchange membrane fuel cell cathodes with a focus on simultaneously improving activity and stability. To this end, novel computational modeling techniques have been developed and applied to acquire knowledge crucial for accelerating the pace of M–N–C catalyst development. In this review, recent progress in computational method development, as well as the predictions of chemical structure of active sites, reaction pathways, ORR kinetics, and catalyst stability in electrochemical environments, are critically surveyed. Moreover, the crucial role of computational modeling to elucidate the functional mechanism of M–N–C catalysts for ORR in acid media and enable rational design of M–N–C catalysts is discussed with a visionary outlook for the field.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
NASA NTRS1988

Oxidation of indole-3-acetic acid to oxindole-3-acetic acid by an enzyme preparation from Zea mays

Indole-3-acetic acid is oxidized to oxindole-3-acetic acid by Zea mays tissue extracts. Shoot, root, and endosperm tissues have enzyme activities of 1 to 10 picomoles per hour per milligram protein. The enzyme is heat labile, is soluble, and requires oxygen for activity. Cofactors of mixed function oxygenase, peroxidase, and intermolecular dioxygenase are not stimulatory to enzymic activity. A heat-stable, detergent-extractable component from corn enhances enzyme activity 6- to 10-fold. This is the first demonstration of the in vitro enzymic oxidation of indole-3-acetic acid to oxindole-3-acetic acid in higher plants.

NASA Discipline Number 40-10↗
DOE OSTI2024

Chemical changes from N-doped graphene and Metal-Organic Frameworks to N-G/MOF composites for improved electrocatalytic activity

Integrating N doped graphene (N G) with Metal Organic Frameworks (MOFs) enhances catalytic activity for oxygen reduction reaction (ORR), often exceeding both the performances of their precursors and, in some cases, even PGM based catalysts. However, the factors driving this improved catalytic activity in N G/MOF composites remain unexplored, particularly from the perspective of the chemical changes. To investigate the chemical changes in N G and MOF upon their integration and the implications of these changes on ORR catalytic activity, an N G/MOF was synthesized from N G with a MOF (ZIF 8) following a mechanochemical wet ball milling process. The N G, ZIF 8, and N G/MOF samples were examined for changes in elemental composition, chemical state of carbon, different nitrogen and carbon bonds, and other chemical interactions. In the N G/MOF catalyst, compared to its N G and ZIF 8 precursors, the relative oxygen content increased, indicating the formation of additional oxygen containing groups. The C 1s peak shifted to a lower binding energy in N G/MOF, suggesting changes in the overall chemical or oxidation state of the carbon atoms. Besides, the increase in pyridinic N functional groups in N G/MOF points to the formation of additional active sites. Furthermore, the formation of C Zn bonds in N G/MOF suggests the probable emergence of single atom Zn sites, while the increase in C=O bonds points to the formation of carboxyl or carbonyl groups. These chemical changes could be linked to the enhanced electrocatalytic activity of the N G/MOF composite for ORR. In conclusion, this study may also be beneficial for other research focused on developing composite catalysts involving various N G and MOF materials.

25 ENERGY STORAGE↗
DOE OSTI2020

Stabilizing Reversible Oxygen Redox Chemistry in Layered Oxides for Sodium‐Ion Batteries

Abstract Triggering oxygen‐related activity is demonstrated as a promising strategy to effectively boost energy density of layered cathodes for sodium‐ion batteries. However, irreversible lattice oxygen loss will induce detrimental structure distortion, resulting in voltage decay and cycle degradation. Herein, a layered structure P2‐type Na 0.66 Li 0.22 Ru 0.78 O 2 cathode is designed, delivering reversible oxygen‐related and Ru‐based redox chemistry simultaneously. Benefiting from the combination of strong Ru 4d‐O 2p covalency and stable Li location within the transition metal layer, reversible anionic/cationic redox chemistry is achieved successfully, which is proved by systematic bulk/surface analysis by in/ex situ spectroscopy (operando Raman and hard X‐ray absorption spectroscopy, etc.). Moreover, the robust structure and reversible phase transition evolution revealed by operando X‐ray diffraction further establish a high degree reversible (de)intercalation processes (≈150 mAh g −1 , reversible capacity) and long‐term cycling (average capacity drop of 0.018%, 500 cycles).

Cao, Xin↗
NASA NTRS2006

Hydrogen Reduction of Ilmenite from Lunar Regolith

Each ascent vehicle returning from the lunar surface with a crew vehicle will require several tons of fuel. Most architecture studies of lunar exploration vehicles use liquid oxygen for fuel, either for LOX/LH2 or LOX/methane. Utilization of oxygen generated on the lunar surface saves mass launched from Earth, with a multiplication factor on the order of 4-5, e.g. production and utilization of 4 tons of lunar oxygen for the ascent vehicle saves 16-20 tons of initial mass in low Earth orbit (IMLEO). The paper discusses ongoing MSFC activity on oxygen production by hydrogen reduction of Ilmenite. Specifically the important project milestone is to develop the Technology Readiness Level for the generation of lunar oxygen for propellant production from 3 to 5. The paper will provide an overview of the processes for Oxygen Generation, Complete Systems Architecture for a pilot lunar plant, experimental apparatus development and initial experimental results, and future directions.

Ramachandran, N.↗
DOE OSTI2022

p-Block Metal Oxide Noninnocence in the Oxygen Evolution Reaction in Acid: The Case of Bismuth Oxide

The Pourbaix diagrams of p-block Pb, Sb, and Bi establish a robust stability for their oxides in acidic solutions. Such oxides have found utility as stable frameworks to support metals that are active for oxygen evolution reaction (OER) catalysis, but they also possess two-electron redox couples, which can potentially engender OER activity. Thus, the use of p-block oxide supports provides an imperative for understanding the OER activity of the unary oxides. Toward this end, we report BiO x films that are able to perform OER catalysis at moderate overpotentials for extended periods of operation (>110 h) in highly acidic solutions (pH 1.0–2.25) with no sign of decreased OER activity during operation at current densities of 1–5 mA cm –2 . X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and UV-vis spectroelectrochemistry reveal a change in the Bi oxidation state prior to OER catalysis, from predominantly Bi 3+ in the as-deposited films to primarily Bi 5+ in the catalytically active films. Furthermore, this transformation is accompanied by a prominent color change from orange to dark brown. Simulations of the cyclic voltammogram catalytic profiles suggest two OER pathways for BiO x involving Bi IV O x and Bi V O x catalysts with the Bi V O x pathway prevailing after catalyst activation. Together, these results demonstrate the ability of BiO x to facilitate OER in acid with high functional stability and underscore the noninnocent role that p-block metal oxides may play in OER catalysis in acidic media.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Tuning of lattice oxygen reactivity and scaling relation to construct better oxygen evolution electrocatalyst

Developing efficient and low-cost electrocatalysts for oxygen evolution reaction is crucial in realizing practical energy systems for sustainable fuel production and energy storage from renewable energy sources. However, the inherent linear scaling relation for most catalytic materials imposes a theoretical overpotential ceiling, limiting the development of efficient electrocatalysts. Herein, using modeled Na x Mn 3 O 7 materials, we report an effective strategy to construct better oxygen evolution electrocatalyst through tuning both lattice oxygen reactivity and scaling relation via alkali metal ion mediation. Specifically, the number of Na + is linked with lattice oxygen reactivity, which is determined by the number of oxygen hole in oxygen lone-pair states formed by native Mn vacancies, governing the barrier symmetry between O–H bond cleavage and O–O bond formation. On the other hand, the presence of Na + could have specific noncovalent interaction with pendant oxygen in *OOH to overcome the limitation from linear scaling relation, reducing the overpotential ceiling. Combining in situ spectroscopy-based characterization with first-principles calculations, we demonstrate that an intermediate level of Na + mediation (NaMn 3 O 7 ) exhibits the optimum oxygen evolution activity. This work provides a new rational recipe to develop highly efficient catalyst towards water oxidation or other oxidative reactions through tuning lattice oxygen reactivity and scaling relation.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Surface restructuring of a perovskite-type air electrode for reversible protonic ceramic electrochemical cells

Reversible protonic ceramic electrochemical cells (R-PCECs) are ideally suited for efficient energy storage and conversion; however, one of the limiting factors to high performance is the poor stability and insufficient electrocatalytic activity for oxygen reduction and evolution of the air electrode exposed to the high concentration of steam. Here we report our findings in enhancing the electrochemical activity and durability of a perovskite-type air electrode, Ba 0.9 Co 0.7 Fe 0.2 Nb 0.1 O 3-δ (BCFN), via a water-promoted surface restructuring process. Under properly-controlled operating conditions, the BCFN electrode is naturally restructured to an Nb-rich BCFN electrode covered with Nb-deficient BCFN nanoparticles. When used as the air electrode for a fuel-electrode-supported R-PCEC, good performances are demonstrated at 650 °C, achieving a peak power density of 1.70 W cm –2 in the fuel cell mode and a current density of 2.8 A cm –2 at 1.3 V in the electrolysis mode while maintaining reasonable Faradaic efficiencies and promising durability.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2020

Sodium tungstate-promoted CaMnO 3 as an effective, phase-transition redox catalyst for redox oxidative cracking of cyclohexane

Oxidative cracking, which combines catalytic oxidation and cracking reactions, represents a promising approach to reduce the energy and carbon intensities for light olefin production from naphtha. The need to co-feed gaseous oxygen with hydrocarbons, however, leads to significant CO x formation and safety concerns. The cost and energy consumption associated with air separation also affects its economic attractiveness. In this study, we investigated a redox oxidative cracking (ROC) scheme and evaluated perovskites (La 0.8 Sr 0.2 FeO 3 and CaMnO 3 ) and Na 2 WO 4 -promoted perovskite (La 0.8 Sr 0.2 FeO 3 @Na 2 WO 4 and CaMnO 3 @Na 2 WO 4 ) as the redox catalysts for ROC. CaMnO 3 @Na 2 WO 4 redox catalyst shows high activity, selectivity, and stability for light olefin production from cyclohexane. Operated under a redox oxidative cracking (ROC) scheme, CaMnO 3 @Na 2 WO 4 enhances the catalytic cracking of cyclohexane, while showing high selectivity towards hydrogen combustion with its built-in, active lattice oxygen. Over three-fold increase in olefin yield compared to thermal cracking and 35% yield increase compared to conventional O 2 -cofeed oxidative cracking were achieved. Low energy ion scattering (LEIS), X-ray photoelectric spectroscopy (XPS), and differential scanning calorimetry (DSC) indicated a core-shell structure, where a molten Na 2 WO 4 layer covers the CaMnO 3 core. Na 2 WO 4 modifies the oxygen donation behavior of CaMnO 3 and provides a catalytically active surface for cyclohexane activation. In-situ XRD revealed that CaMnO 3 @Na 2 WO 4 exhibited excellent structural stability and regenerability. The transformation of Mn 4+ ↔ Mn 3+ ↔ Mn 2+ in CaMnO 3 , facilitated by reversible phase transition to (Ca/Mn)O solid solution, is responsible for the lattice oxygen donation and uptake during redox cycles. Electrochemical impedance spectroscopy (EIS) measurements further confirmed that the oxygen species were transported through the molten Na 2 WO 4 layer to participate in ROC. These findings offer mechanistic insights to design effective redox catalysts for hydrocarbon valorization using the chemical looping strategy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Enhancing the activity of Fe-N-C oxygen reduction reaction electrocatalysts by high-throughput exploration of synthesis parameters

Here, the most active class of platinum group metal-free (PGM-free) oxygen reduction reaction (ORR) electrocatalysts in acidic electrolytes are those synthesized by heat treatment of iron, carbon, nitrogen precursors (Fe-N-C). Due to the large number of possible precursor compounds, a small fraction of the synthesis variable space has been explored. Correlation of synthesis variables with Fe speciation and ORR activity has been limited. In this work, an automation platform and a multi-port ball-milling were utilized to evaluate the effects of synthesis variables, such as identity of iron precursor, iron loading, and carbon and nitrogen sources on the ORR activity of iron -nitrogen-carbon catalysts in acidic electrolyte. The ORR activity is correlated with catalyst Fe speciation determined using Fe K-edge X-ray absorption spectroscopy (XAFS).

30 DIRECT ENERGY CONVERSION↗
NASA NTRS1994

High temperature sorbents for oxygen

A sorbent capable of removing trace amounts of oxygen (ppt) from a gas stream at a high temperature above 200 C comprising a porous alumina silicate support, such as zeolite, containing from 1 to 10 percent by weight of ion exchanged transition metal, such as copper or cobalt ions, and 0.05 to 1.0 percent by weight of an activator selected from a platinum group metal such as platinum is described. The activation temperature, oxygen sorption, and reducibility are all improved by the presence of the platinum activator.

Sharma, Pramod K.↗