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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Wet-Etching of Acoustically Spalled GaAs for Substrate Reuse

Acoustic spalling is a promising technique for substrate reuse in the fabrication of gallium arsenide (GaAs) photovoltaic cells. However, the acoustic spalling process can leave the substrate with areas of rough surface morphology that can interfere with subsequent cell growth and processing. In this work, we investigate the use of wet etchants to smooth the surface of acoustically spalled GaAs substrates. We evaluated six different etchants. Of those tested, an 8:1:1 mixture of sulfuric acid, hydrogen peroxide, and water at 30 degrees C and a moderate stirring rate showed the greatest roughness reduction per mass loss while producing the desired morphology. This etchant was then applied to an acoustically spalled 2-inch GaAs wafer. A single-junction GaAs cell was then grown via metalorganic vapor-phase epitaxy on this substrate, an acoustic spalled substrate without a smoothing etch, and an epi-ready substrate. Use of the 8:1:1 H2SO4:H2O2:H2O etchant produced cells an average efficiency of 12.8% as compared to that of 2.0% grown on the unetched acoustically spalled substrate and 16.3% grown on the epi-ready substrate. The results of this work demonstrate that wet etching is a viable method for smoothing the surface of spalled GaAs substrates, paving the way for substrate reuse via acoustic spalling at efficiencies that approach growth on epi-ready substrates.

etching↗
DOE OSTI2022

Mechanistic assessment of tolerance to iron deficiency mediated by Trichoderma harzianum in soybean roots

Abstract Aims Iron (Fe) deficiency in soil is a continuing problem for soybean (Glycine max L.) production, partly as a result of continuing climate change. This study elucidates how Trichoderma harzianum strain T22 (TH) mitigates growth retardation associated with Fe-deficiency in a highly sensitive soybean cultivar. Methods and Results Soil TH supplementation led to mycelial colonization and the presence of UAOX1 gene in roots that caused substantial improvement in chlorophyll score, photosynthetic efficiency and morphological parameters, indicating a positive influence on soybean health. Although rhizosphere acidification was found to be a common feature of Fe-deficient soybean, the upregulation of Fe-reductase activity (GmFRO2) and total phenol secretion were two of the mechanisms that substantially increased the Fe availability by TH. Heat-killed TH applied to soil caused no improvement in photosynthetic attributes and Fe-reductase activity, confirming the active role of TH in mitigating Fe-deficiency. Consistent increases in tissue Fe content and increased Fe-transporter (GmIRT1, GmNRAMP2a, GmNRAMP2b and GmNRAMP7) mRNA levels in roots following TH supplementation were observed only under Fe-deprivation. Root cell death, electrolyte leakage, superoxide (O2•–) and hydrogen peroxide (H2O2) substantially declined due to TH in Fe-deprived plants. Further, the elevation of citrate and malate concentration along with the expression of citrate synthase (GmCs) and malate synthase (GmMs) caused by TH suggest improved chelation of Fe in Fe-deficient plants. Results also suggest that TH has a role in triggering antioxidant defence by increasing the activity of glutathione reductase (GR) along with elevated S-metabolites (glutathione and methionine) to stabilize redox status under Fe-deficiency. Conclusions TH increases the availability and mobilization of Fe by inducing Fe-uptake pathways, which appears to help provide resistance to oxidative stress associated with Fe-shortage in soybean. Significance and Impact of the Study These findings indicate that while Fe deficiency does not affect the rate or degree of TH hyphal association in soybean roots, the beneficial effects of TH alone may be Fe deficiency-dependent.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Laser writing of nitrogen-doped silicon carbide for biological modulation

Conducting or semiconducting materials embedded in insulating polymeric substrates can be useful in biointerface applications; however, attainment of this composite configuration by direct chemical processes is challenging. Laser-assisted synthesis has evolved as a fast and inexpensive technique to prepare various materials, but its utility in the construction of biophysical tools or biomedical devices is less explored. Here, we use laser writing to convert portions of polydimethylsiloxane (PDMS) into nitrogen-doped cubic silicon carbide (3C-SiC). The dense 3C-SiC surface layer is connected to the PDMS matrix via a spongy graphite layer, facilitating electrochemical and photoelectrochemical activity. We demonstrate the fabrication of arbitrary two-dimensional (2D) SiC-based patterns in PDMS and freestanding 3D constructs. To establish the functionality of the laser-produced composite, we apply it as flexible electrodes for pacing isolated hearts and as photoelectrodes for local peroxide delivery to smooth muscle sheets.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Carbon-free high-performance cathode for solid-state Li-O 2 battery

The development of a cathode for solid-state lithium-oxygen batteries has been hindered in practice by a low capacity and limited cycle life despite their potential for high energy density. Here, a previously unexplored strategy is proposed wherein the cathode delivers a specific capacity of 200 milliampere hour per gram over 665 discharge/charge cycles, while existing cathodes achieve only ~50 milliampere hour per gram and ~100 cycles. A highly conductive ruthenium-based composite is designed as a carbon-free cathode by first-principles calculations to avoid the degradation associated with carbonaceous materials, implying an improvement in stability during the electrochemical cycling. In addition, water vapor is added into the main oxygen gas as an additive to change the discharge product from growth-restricted lithium peroxide to easily grown lithium hydroxide, resulting in a notable increase in capacity. Thus, the proposed strategy is effective for developing reversible solid-state lithium-oxygen batteries with high energy density.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Alkali metal halide–coated perovskite redox catalysts for anaerobic oxidative dehydrogenation of n -butane

Oxidative dehydrogenation (ODH) of n-butane has the potential to efficiently produce butadiene without equilibrium limitation or coke formation. Despite extensive research efforts, single-pass butadiene yields are limited to <23% in conventional catalytic ODH with gaseous O 2 . This article reports molten LiBr as an effective promoter to modify a redox-active perovskite oxide, i.e., La 0.8 Sr 0.2 FeO 3 (LSF), for chemical looping–oxidative dehydrogenation of n-butane (CL-ODHB). Under the working state, the redox catalyst is composed of a molten LiBr layer covering the solid LSF substrate. Characterizations and ab initio molecular dynamics (AIMD) simulations indicate that peroxide species formed on LSF react with molten LiBr to form active atomic Br, which act as reaction intermediates for C–H bond activation. Meanwhile, molten LiBr layer inhibits unselective CO 2 formation, leading to 42.5% butadiene yield. The redox catalyst design strategy can be extended to CL-ODH of other light alkanes such as iso-butane conversion to iso-butylene, providing a generalized approach for olefin production.

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

Solvent molecules form surface redox mediators in situ and cocatalyze O 2 reduction on Pd

Solvent molecules influence the reactions of molecular hydrogen and oxygen on palladium nanoparticles. Organic solvents activate to form reactive surface intermediates that mediate oxygen reduction through pathways distinct from reactions in pure water. Kinetic measurements and ab initio quantum chemical calculations indicate that methanol and water cocatalyze oxygen reduction by facilitating proton-electron transfer reactions. Methanol generates hydroxymethyl intermediates on palladium surfaces that efficiently transfer protons and electrons to oxygen to form hydrogen peroxide and formaldehyde. Formaldehyde subsequently oxidizes hydrogen to regenerate hydroxymethyl. Water, on the other hand, heterolytically oxidizes hydrogen to produce hydronium ions and electrons that reduce oxygen. These findings suggest that reactions of solvent molecules at solid-liquid interfaces can generate redox mediators in situ and provide opportunities to substantially increase rates and selectivities for catalytic reactions.

Adams, Jason S.↗
DOE OSTI2023

A room temperature rechargeable Li 2 O-based lithium-air battery enabled by a solid electrolyte

Lithium-air batteries have scope to compete with gasoline in terms of energy density. However, in most systems, the reaction pathways either involve one- or two-electron transfer, leading to lithium peroxide (Li 2 O 2 ) or lithium superoxide (LiO 2 ), respectively. Kondori et al. investigated a lithium-air battery that uses a ceramic-polyethylene oxide–based composite solid electrolyte and found that it can undergo a four-electron redox reaction through lithium oxide (Li 2 O) formation and decomposition (see the Perspective by Dong and Lu). The composite electrolyte embedded with Li 10 GeP 2 S 12 nanoparticles shows high ionic conductivity and stability and high cycle stability through a four-electron transfer process.

25 ENERGY STORAGE↗
DOE OSTI2024

Direct propylene epoxidation via water activation over Pd-Pt electrocatalysts

Direct electrochemical propylene epoxidation by means of water-oxidation intermediates presents a sustainable alternative to existing routes that involve hazardous chlorine or peroxide reagents. Here, we report an oxidized palladium-platinum alloy catalyst (PdPtO x /C), which reaches a Faradaic efficiency of 66 ± 5% toward propylene epoxidation at 50 milliamperes per square centimeter at ambient temperature and pressure. Embedding platinum into the palladium oxide crystal structure stabilized oxidized platinum species, resulting in improved catalyst performance. The reaction kinetics suggest that epoxidation on PdPtO x /C proceeds through electrophilic attack by metal-bound peroxo intermediates. This work demonstrates an effective strategy for selective electrochemical oxygen-atom transfer from water, without mediators, for diverse oxygenation reactions.

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

OxyR regulates the oxidative stress response in Zymomonas mobilis during oxic growth and anoxic biofuel fermentation

The bacterium Zymomonas mobilis is widely studied for its potential as an industrial biofuel producer. Anoxic fermentation by Z. mobilis in lignocellulosic hydrolysate can generate bioethanol from renewable plant biomass. In this study, we deleted a gene from the Z. mobilis genome encoding a homolog of OxyR, a transcription factor that activates an oxidative stress response in bacteria to reduce reactive oxygen species (ROS). Deletion of this transcription factor inhibited growth of Z. mobilis in oxic, but not anoxic, conditions in laboratory media. A ROS probe revealed that the oxyR response is required to reduce intracellular ROS during oxic growth. Importantly for biofuel production, the absence of oxyR inhibited growth and delayed ethanol production during anoxic hydrolysate fermentation. To determine the source of oxidative stress in hydrolysates, we grew ΔoxyR in a synthetic hydrolysate containing known inhibitors found in hydrolysates. There was no growth defect in ΔoxyR in the synthetic hydrolysate, indicating that known inhibitory compounds are not the source of anoxic oxidative stress. We determined that ammonia-fiber expansion switchgrass hydrolysate contains significant peroxide concentrations. Addition of catalase to hydrolysate improves growth of both ΔoxyR and wild-type Z. mobilis in hydrolysate. This study uncovers an important source of stress to Z. mobilis during biofuel fermentation.

OxyR↗
DOE OSTI2026

Transcriptomic data sets examining several stress responses in Zymomonas mobilis strains

We used RNA-seq to compare gene expression from Zymomonas mobilis ZM4 grown under various conditions: aerobic ± paraquat, anaerobic ± hydrogen peroxide, or an iron chelator. We analyzed two mutant strains lacking predicted transcription factors (ZMO_0442 and ZMO_1411) grown under aerobic or anaerobic conditions. We report the RNA-seq data from these experiments.

Bacterial Stress Response↗
DOE OSTI2020

Global Network Analysis of Neisseria gonorrhoeae Identifies Coordination between Pathways, Processes, and Regulators Expressed during Human Infection

Neisseria gonorrhoeae is a Gram-negative diplococcus that is responsible for the sexually transmitted infection gonorrhea, a high-morbidity disease in the United States and worldwide. Over the past several years, N. gonorrhoeae strains resistant to antibiotics used to treat this infection have begun to emerge across the globe. Thus, new treatment strategies are needed to combat this organism. Here, we utilized N. gonorrhoeae transcriptomic data sets, including those obtained from natural infection of the human genital tract, to infer the first global gene coexpression network of this pathogen. Interrogation of this network revealed genes central to the network that are likely critical for gonococcal growth, metabolism, and virulence, including genes encoding hypothetical proteins expressed during mucosal infection. In addition, network analysis revealed overlap in the response of N. gonorrhoeae to incubation with neutrophils and exposure to hydrogen peroxide stress in vitro. Network analysis also identified new targets of the gonococcal global regulatory protein Fur, while examination of the network neighborhood of genes allowed us to assign additional putative categories to several proteins. Collectively, the characterization of the first gene coexpression network for N. gonorrhoeae described here has revealed new regulatory pathways and new categories for proteins and has shown how processes important to gonococcal infection in both men and women are linked. This information fills a critical gap in our understanding of virulence strategies of this obligate human pathogen and will aid in the development of new treatment strategies for gonorrhea.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Probing Membrane Degradation with Varying Catalyst Layer Thickness and Carbon Support

Understanding membrane degradation continues to be of significant importance when studying fuel cell durability. Fuel cell performance and durability depends heavily on the membrane's chemical and mechanical integrity. In Nafion® membranes, hydroxyl radicals are the primary cause of chemical membrane degradation as they attack the membrane's polymer structure. Radical formation can ensue via peroxide decomposition at the cathode or gases reacting on Pt particles within the membrane. Here, a previous research effort on membrane degradation as a function of ultra-low Pt loadings (≤ 0.1 mgPt cm -2 ) showed the degradation rate increases with Pt loading. This is most likely due to more heterogenous sites for radical formation. Manufacturing MEAs with ultra-low Pt loadings can yield thin, non-uniform catalyst layers. In this research effort we studied membrane degradation with ultra-low Pt loadings while varying catalyst layer thickness, I/C ratio, and types of carbon support.

25 ENERGY STORAGE↗
DOE OSTI2021

Editors’ Choice—Diffusion Media for Cation Contaminant Transport Suppression into Fuel Cell Electrodes

Polymer electrolyte membrane fuel cells provide an alternative option to fossil fuel-based energy conversion devices. However, the corrosion of fuel cell components, specifically the bipolar plates, introduces contaminants (e.g., Fe, Ni) into the membrane electrode assembly (MEA). These contaminants accelerate the ionomer degradation by acting as a Fenton’s reagent, decreasing the fuel cell’s durability. This study presents the mechanism and the diffusion media properties affecting the transport of cation contaminants into the MEA. Cation contaminant transport was studied after altering the gas diffusion layers (GDLs) wettability, emulating the GDL properties after prolonged operation, by ex situ hydrogen peroxide treatment or in situ electrochemical potential cycling. A GDL with crack-free microporous layer (MPL) showed a lower cation transport rate to the catalyst layer than MPL with cracks after both ex situ and in situ treatment. A novel GDL was developed from modification of the conventional GDL via the addition of a hydrophobic layer to the GDL substrate, which suppressed the contaminant cation transport significantly. This novel GDL also showed improved fuel cell performance.

25 ENERGY STORAGE↗
DOE OSTI2021

Electrolyte Takeover Strategy for Performance Recovery in Polysulfide-Permanganate Flow Batteries

The abundance of active material precursors for a polysulfide-permanganate flow battery makes it a compelling chemistry for large-scale, and potentially long-duration (>10 h), grid electricity storage. Precipitation, arising from either reactant crossover or electrolyte side reactions, decrease cell efficiencies during charge/discharge cycling. Regardless of the abundance and low cost of active materials, a system without high cyclability cannot meet grid electricity storage economic targets for applications that cycle regularly. Precipitated species can be removed, and reactor efficiency performance restored, by using an electrolyte takeover process, or ETP. Two ETP methods are investigated. One ETP uses the negative electrolyte, an alkaline polysulfide (pS) solution, as takeover solution, and another uses dilute acidic peroxide (DAP) as the takeover solution. Both ETPs maintain functional cell operation within an acceptable performance range over >1000 h and >200 cycles, a duration over which cells that do not undergo ETPs clog and fail. The DAP ETP proves especially effective and limits irrecoverable voltage efficiency fade below 0.02%/cycle. These ETPs, either individually, or in combination, can enable the requisite cyclability for practical polysulfide-permanganate flow battery systems.

25 ENERGY STORAGE↗
DOE OSTI2022

Ion Chromatography and Combustion Ion Chromatography Analysis of Fuel Cell Effluent Water During Open Circuit Voltage

Open circuit voltage tests were conducted on sixteen 3M Ionomer and eight Nafion™ NR211 membranes. Lifetime distributions were determined, and ion chromatography (IC) techniques were used to measure fluoride, sulfate, trifluoro acetate, and oxalate ions. Combustion Ion Chromatography (CIC) was used to determine the total organic fluoride (TOF) associated with water soluble membrane degradation fragments. The ratio of these products relative to the fluoride release rates were used to infer the likely degradation mechanism for each membrane. Peroxide attack at the sulfonic acid side chain was determined to be the least relevant reaction pathway while the long-proposed polymer chain end unzipping appears to be the dominant mechanism. Abstraction of the tertiary fluorine in the NR211 backbone and side chain is evident by organic fluoride release rates higher than can be explained by unzipping alone.

25 ENERGY STORAGE↗
DOE OSTI2023

Membrane Pretreatment and Cell Conditioning for Proton Exchange Membrane Water Electrolysis

As the research community studying proton exchange membrane water electrolysis (PEMWE) grows, it is important to develop methods that achieve transparent, reproducible research. Reproducibility of performance and durability is a challenge facing the PEMWE field, as the published literature includes a wide spread of results obtained with nominally similar materials. Prior round-robin performance benchmarking efforts [1] have identified inadequate cell conditioning as a major source of variation in apparent cell performance. Inadequate pre-treatment and conditioning can lead to instability in initial performance and adds ambiguity to durability measurements. However, excessively prolonged conditioning procedures limit the throughput of testing and the pace of research. Pretreatment and conditioning methods vary significantly across the research literature, but little systematic investigation is available into the mechanisms of these procedures or how procedural differences may impact results. This presentation will discuss investigations into the effects of membrane pre-treatment and operating procedures during cell conditioning on initial performance and catalyst-specific accelerated stress tests, with the aim of recommending procedures to enable clear, reproducible, and high-throughput research. Methods investigated include the use of hydrogen peroxide, acids, and hydration at elevated temperature for membrane pretreatment, and conditioning procedures such as current or voltage holds and cycling. The investigations cover both the impacts of these procedures on cell performance and stability as well as underlying mechanisms and processes taking place in the cell materials.

cell↗
DOE OSTI2020

Skeletal tissue regulation by catalase overexpression in mitochondria

Accumulation of oxidative damage from excess reactive oxygen species (ROS) may contribute to skeletal aging and mediate adverse responses to physiological challenges. Wild-type (WT) mice and transgenic mice (male, 16 wk of age) with human catalase targeted to the mitochondria (mCAT) were analyzed for skeletal responses to the remodeling stimuli of combined hind-limb unloading and exposure to ionizing radiation ( 137 Cs, 2 Gy). Treatment for 2 wk caused lipid peroxidation in the bones WT but not mCAT mice, showing that transgene expression mitigated oxidative stress. Ex vivo osteoblast colony growth rate was 95% greater in mCAT than WT mice and correlated with catalase activity levels ( P < 0.005, r = 0.67), although terminal osteoblast and osteoclast differentiation were unaffected. mCAT mice had lower cancellous bone volume and cortical size than WT mice. Ambulatory control mCAT animals also displayed reduced cancellous and cortical structural properties compared with control WT mice. In mCAT but not WT mice, treatment caused an unexpectedly rapid radial expansion (+8% cortical area, +22% moment of inertia), reminiscent of compensatory bone growth during advancing age. In contrast, treatment caused similar structural deficits in cancellous tissue of mCAT and WT mice. In sum, mitochondrial ROS signaling via H 2 O 2 was important for the acquisition of adult bone structure and catalase overexpression failed to protect cancellous tissue from treatment. In contrast, catabolic stimuli caused radial expansion in mCAT not WT mice, suggesting that mitochondrial ROS in skeletal cells act to suppress tissue turnover in response to remodeling challenges.

Cell Biology↗
DOE OSTI2020

COVID-19 global pandemic planning: Performance and electret charge of N95 respirators after recommended decontamination methods

Shortages of N95 respirators for use by medical personnel have driven consideration of novel conservation strategies, including decontamination for reuse and extended use. Decontamination methods listed as promising by the Centers for Disease Control and Prevention (CDC) (vaporous hydrogen peroxide (VHP), wet heat, ultraviolet irradiation (UVI)) and several methods considered for low resource environments (bleach, isopropyl alcohol and detergent/soap) were studied for two commonly used surgical N95 respirators (3M™ 1860 and 1870+ Aura™). Although N95 filtration performance depends on the electrostatically charged electret filtration layer, the impact of decontamination on this layer is largely unexplored. As such, respirator performance following decontamination was assessed based on the fit, filtration efficiency, and pressure drop, along with the relationship between (1) surface charge of the electret layer, and (2) elastic properties of the straps. Decontamination with VHP, wet heat, UVI, and bleach did not degrade fit and filtration performance or electret charge. Isopropyl alcohol and soap significantly degraded fit, filtration performance, and electret charge. Pressure drop across the respirators was unchanged. Modest degradation of N95 strap elasticity was observed in mechanical fatigue testing, a model for repeated donnings and doffings. CDC recommended decontamination methods including VHP, wet heat, and UV light did not degrade N95 respirator fit or filtration performance in these tests. Extended use of N95 respirators may degrade strap elasticity, but a loss of face seal integrity should be apparent during user seal checks. NIOSH recommends performing user seal checks after every donning to detect loss of appropriate fit. Decontamination methods which degrade electret charge such as alcohols or detergents should not be used on N95 respirators. The loss of N95 performance due to electret degradation would not be apparent to a respirator user or evident during a negative pressure user seal check.

60 APPLIED LIFE SCIENCES↗