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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Effects of Potassium Permanganate Oxidation on Subsurface Microbial Activity

In situ chemical oxidation has the potential for degrading large quantities of organic contaminants and can be more effective and timely than traditional ex situ treatment methods. However, there is a need to better characterize the potential effects of this treatment on natural processes. This study focuses on potential inhibition to anaerobic dechlorination of trichloroethene (TCE) in soils from a large manufacturing facility as a result of in situ oxidation using potassium permanganate (KMn04)Previous microcosm studies established that natural attenuation occurs on-site and that it is enhanced by the addition of ethanol to the system. A potential remediation scheme for the site involves the use of potassium permanganate to reduce levels of TCE in heavily contaminated areas, then to inject ethanol into the system to "neutralize" excess oxidant and enhance microbial degradation. However, it is currently unknown whether the exposure of indigenous microbial populations to potassium permanganate may adversely affect biological reductive dechlorination by these microorganisms. Consequently, additional microcosm studies were conducted to evaluate this remediation scheme and assess the effect of potassium permanganate addition on biological reductive dechlorination of TCE. Samples of subsurface soil and groundwater were collected from a TCE-impacted area of the site. A portion of the soil was pretreated with nutrients and ethanol to stimulate microbial activity, while the remainder of the soil was left unamended. Soil/groundwater microcosms were prepared in sealed vials using the nutrient-amended and unamended soils, and the effects of potassium permanganate addition were evaluated using two permanganate concentrations (0.8 and 2.4 percent) and two contact times (1 and 3 weeks). TCE was then re-added to each microcosm and TCE and dichloroethene (DCE) concentrations were monitored to determine the degree to which microbial dechlorination occurred following chemical oxidation. Evidence of microbial degradation was generally detected within four weeks after TCE addition. Increases in DCE concentrations were consistent with decreases in TCE. The concentration of TCE in the nutrient-amended samples exposed to 2.4% KMnO4 for one week degraded somewhat more slowly than the samples exposed to the 0.8% KMnO4. The rates of degradation did not correlate with the length of KMn04 exposure for the nutrient-amended microcosms. Microbial degradation of TCE in the unamended microcosms was generally similar to that observed in the nutrient-amended microcosms. One treatment condition (unamended, one week exposure, 2.4% KMnO4) was exposed to elevated levels of ethanol and showed little evidence of degradation. It is suspected that the high levels of ethanol were toxic to the microorganisms. The results of the study indicate that exposure of indigenous soil and groundwater microbial populations to KMnO4 at concentrations of 0.8 to 2.4% do not impair the ability of the microbial populations to dechlorinate TCE. Consequently, the combination of chemical oxidation followed by enhanced biological reductive dechlorination appears to be a viable remedial strategy for highly-impacted subsurface areas of the site.

Rowland, Martin A.↗
DOE OSTI2024

Hybrid Density Functional Theory Comparison of Oxygen Release and Solvent Decomposition Kinetics on Li x NiO 2 Surfaces

High-nickel-content layered oxides are among the most promising electric vehicle battery cathode materials. However, their interfacial reactivity with electrolytes and tendency toward oxygen release (possibly yielding reactive 1 O 2 ) remain degradation concerns. Elucidating the most relevant (i.e., fastest) interfacial degradation mechanism will facilitate future mitigation strategies. We apply screened hybrid density functional (HSE06) calculations to compare the reaction kinetics of Li x NiO 2 surfaces with ethylene carbonate (EC) with those of O 2 release. Further, on both the (001) and (104) facets, EC oxidative decomposition exhibits lower activation energies than O 2 release. Our calculations, coupled with previously computed liquid-phase reaction rates of 1 O 2 with EC, strongly question the role of “reactive 1 O 2 ” species in electrolyte oxidative degradation. The possible role of other oxygen species is discussed. To deal with the challenges of modeling Li x NiO 2 surface reactivity, we emphasize a “local structure” approach instead of pursuing the global energy minimum.

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

Direct kinetic measurements and theoretical predictions of an isoprene-derived Criegee intermediate

Isoprene has the highest emission into Earth’s atmosphere of any nonmethane hydrocarbon. Atmospheric processing of alkenes, including isoprene, via ozonolysis leads to the formation of zwitterionic reactive intermediates, known as Criegee intermediates (CIs). Direct studies have revealed that reactions involving simple CIs can significantly impact the tropospheric oxidizing capacity, enhance particulate formation, and degrade local air quality. Methyl vinyl ketone oxide (MVK-oxide) is a four-carbon, asymmetric, resonance-stabilized CI, produced with 21 to 23% yield from isoprene ozonolysis, yet its reactivity has not been directly studied. We present direct kinetic measurements of MVK-oxide reactions with key atmospheric species using absorption spectroscopy. Direct UV-Vis absorption spectra from two independent flow cell experiments overlap with the molecular beam UV-Vis-depletion spectra reported recently [M. F. Vansco, B. Marchetti, M. I. Lester, J. Chem. Phys. 149, 44309 (2018)] but suggest different conformer distributions under jet-cooled and thermal conditions. Comparison of the experimental lifetime herein with theory indicates only the syn -conformers are observed; anti -conformers are calculated to be removed much more rapidly via unimolecular decay. We observe experimentally and predict theoretically fast reaction of syn -MVK-oxide with SO 2 and formic acid, similar to smaller alkyl-substituted CIs, and by contrast, slow removal in the presence of water. We determine products through complementary multiplexed photoionization mass spectrometry, observing SO 3 and identifying organic hydroperoxide formation from reaction with SO 2 and formic acid, respectively. The tropospheric implications of these reactions are evaluated using a global chemistry and transport model.

09 BIOMASS FUELS↗
DOE OSTI2026

Phosphonic-Acid-Reinforced Polymer Hole Transport Layers for Deployable p-i-n Perovskite Photovoltaics

The long-term durability prospects of halide perovskite solar cells are rapidly improving; however, the interface between the hole transport layer (HTL) and the perovskite remains a source of degradation. Alone, polymer- or carbazole-based HTLs suffer from incomplete coverage of the underlying indium tin oxide glass, leading to degradation and compromised performance. Here, we show a multi-HTL approach whereby a polymer HTL is reinforced using a phosphonic acid modification leading to better protection of the buried perovskite interface and more columnar growth of perovskite film, resulting in an ~40-mV open-circuit voltage (VOC) improvement indicative of suppressed interfacial recombination across multiple p-i-n device architectures. Solar cells with this reinforced HTL show higher tolerance to several accelerated stress tests. We report, among the best durabilities for unencapsulated cells, a T90 ~3,000 h (T80 ~5,900 h) at 65 degrees C under continuous 1.2 sun AM 1.5G illumination and maximum power point tracking, representing a nearly 4-fold increase compared with [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz)-only devices. Furthermore, we deployed a device with this reinforced HTL on a cube satellite, with long-duration operational space testing results exceeding T80 for the complete mission duration of ~100 days in low Earth orbit.

14 SOLAR ENERGY↗
DOE OSTI2021

Tandem Catalytic Antioxidant Nanoparticles Comprising Cerium Carbonate and Photoactive Metal Oxides

While photoactive metal oxides such as TiO 2 find widespread use in paints and coatings as well as cosmetics and suncare products, they also generate reactive oxygen species (ROS), which degrade materials and are associated with human-health pathologies. Here, we demonstrate a robust and potent catalytic antioxidant consisting of earth-abundant cerium carbonate nanoparticles and micron-size Ce 2 (CO 3 ) 3 . 8H 2 O, which are characterized by powder X-ray diffraction and scanning nanobeam electron diffraction. When dispersed with photoactive metal oxides, these cerium carbonate catalysts decrease the photodecomposition rate of organic dyes and commercial pigment colorants in aqueous media by up to 820-fold, as well as in acrylic coatings. X-ray photoelectron spectroscopy and kinetic experiments support the same tandem catalysis mechanism of photoprotection when using both micron-size Ce 2 (CO 3 ) 3 . 8H 2 O and cerium carbonate nanoparticles. This mechanism involves ROS disproportionation (catalyzed by cerium carbonate) and H 2 O 2 decomposition (partially catalyzed by TiO 2 ) pathways, both of which cerium carbonate also catalyzes on its own, crudely mimicking the function of the cascade system of superoxide dismutase and catalase enzymes. When cerium carbonate nanoparticles were dispersed at 2 wt % in polymethylmethacrylate, the transparency of the polymer film was preserved and the photo-oxidative degradation of the polymer was prevented following UV irradiation at 254 nm, which otherwise resulted in the loss of optical properties and hydroxylation as characterized by ATR-FTIR spectroscopy, in the control polymer lacking cerium carbonate. Similar observations were made regarding color preservation in paint films comprising dye and insoluble commercial colorant pigments. The material chemistry associated with this photoprotection catalysis is subtle and emphasizes the importance of both Ce(III) and carbonate together, as both CePO 4 and Na 2 CO 3 are inactive. In conclusion, this emphasis is also apparent in comparisons of photoprotection catalysis with previously reported cerium oxide nanoparticles, which are significantly less active compared with Ce 2 (CO 3 ) 3 . 8H 2 O under the same conditions.

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

Collaborative Research Proposal: Time Resolved Optical Emissions Spectroscopy and Laser Induced Fluorescence Spectroscopy of Nanosecond Pulsed Discharges in a Gas-Liquid Water Film Reactor

Electrical discharge plasma formed in contact with liquid water is of interest for a wide range of applications in chemical, biomedical, agricultural, electrical, and materials science and engineering. Such plasma reactors are of very timely importance since they also have significant disinfection capability by inactivating bacteria, viruses and other pathogens. Many types of plasma sources including those driven by AC, DC, RF, microwave, and pulsed electrical power supplies coupled to a wide range of different electrode configurations and reactor designs have been developed and explored which contact the plasma with liquid water. Recent roadmaps have recommended that further work is needed to develop our understanding of the fundamental chemical and physical process which occur at the interface of non-thermal plasma with liquid water solutions in order to advance this large diversity of applications which ultimately depend upon efficient production of key reactive chemical species. There is a wide range of interacting factors that affect the chemical reactions that occur in the plasma, in the liquid phase, and at the interface. These factors ultimately govern the key reactive chemical species formed and used in the various applications and they include a) the reactor design and input parameters, b) the discharge and transport processes, c) the plasma properties, and d) the resulting chemical reactions. For pulsed discharges, the power supply design and output parameters control the applied voltage, frequency, rise time, and width (duration) of the applied pulses. The reactor design involves specification of the gas-liquid contacting methods, electrode gap distance, reactor volume and shape, and gas and liquid flow rates achievable. The gas and liquid compositions as well as the liquid properties such as pH and conductivity are also of key importance in determination of the resulting chemical reactions. In addition, the important plasma properties include plasma gas temperature, electron density, electron energy (distribution), and size of the plasma channels which are all affected by the discharge and transport properties. Many studies have focused on specific aspects of these various processes. Of particular important and relevance to the proposed work is the utilization of nanosecond pulses to generate plasma in gas-liquid systems, liquid bubbles, underwater, and in gases. Recent advances in nanosecond pulses provide significant advantages in utilization with liquid water. For example, fast rise time and short pulses are less sensitive to water conductivity, such short pulses may provide advantages in fast temporal quenching of the plasma, and fundamental analysis of pulse properties, including pulse shape and width, may be facilitated by investigation of single filamentary fast pulses. Many studies have also dealt with the role of the gas composition on formation of reactive oxygen species (ROS) (i.e., hydroxyl radicals – ·OH, hydrogen peroxide – H 2 O 2 , various atomic oxygen species, ozone-O 3 , hydroperoxyl radicals HO 2 ·) and reactive nitrogen species (RNS) (i.e., nitrogen oxides – NO, NO 2 , N 2 O - collectively termed NO X , nitrite-NO 2 - , nitrate-NO 3 - , peroxynitrite-ONOO - ). The hydroxyl radical is the critical species in many chemical oxidation reactions for chemical degradation of toxic compounds in water and gases and for synthesis of some compounds. The mixture of various nitrogen oxide species is important for many biochemical and biological processes involved in biomedical and agricultural applications including disinfection and fertilizer production. The present proposal focuses on determination of the effects of time resolved electron density and hydroxyl radicals on plasma chemical reactions through collaboration with the Princeton Collaborative Low Temperature Plasma Research Facility (PCRF) at the Princeton Plasma Physics Laboratory (PPPL). In order to further investigate the role of the plasma generated electrons and hydroxyl radicals on the overall formation of the key species including hydrogen peroxide, hydroxyl radicals, and nitrogen oxides, the proposed work, thus seeks to determine high resolution time resolved electron density by optical emissions spectroscopy and time resolved hydroxyl radicals using laser induced fluorescence in the nanosecond discharge reactor. The combination of data on electron density and hydroxyl radical concentration will be utilized in the present work to more fully characterize the chemical reaction processes in this system and to advance the design, development, and operation of such chemical reactors for a wide range of applications.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Propylamine Functionalized Porous Fiber Sorbents with High Oxidation Stability for Direct Air Capture

Amine-based sorbents are highly effective for direct air capture (DAC) due to their excellent CO2 capture efficiency under ultra-dilute conditions. However, these sorbents can suffer degradation when exposed to combinations of heat, oxygen, and other atmospheric components, indicating a need for improved sorbent stability. In this study, we developed amidoxime functionalized polymer of intrinsic microporosity (PIM-1-AO) fibers with tethered amines, specifically tris(2-aminoethyl)amine (TAEA) and tris(3-aminopropyl)amine (TAPA), denoted as PIM-1-AO-TAEA and PIM-1-AO-TAPA, respectively. In addition, large scale sorbent fiber spinning has been successfully performed by producing meters of fibers in the lab. We demonstrated that substituting TAEA with TAPA, which has propyl chains instead of ethyl chains, reduces oxidative degradation under regeneration conditions. The findings revealed that PIM-1-AO-TAPA not only significantly outperforms PIM-1-AO-TAEA after accelerated aging process, but also outperforms any other sorbent used in DAC aged under similar conditions. Moreover, PIM-1-AO-TAPA sorbent fibers showed one of the highest amine efficiencies (0.25) considering the low amine loading (21%) coupled with robust CO2 uptake performance (1.12 mmol/g) under DAC conditions.

amine-based sorbent↗
DOE OSTI2020

Highly-Active and Contaminant-Tolerant Cathodes for Durable Solid Oxide Fuel Cells (Final Report)

The objective of this project is to investigate the fundamental degradation methods occurring in solid oxide fuel cell (SOFC) cathodes when exposed to chromium and carbon dioxide contamination and to rationally design alkaline earth-based catalysts to increase stability and tolerance to contaminate poisoning. With a mechanistic and fundamental understanding of the degradation methods, advanced catalytic surface modifications can be applied to reduce degradation. The specific technical objectives are: (1) To identify/develop new catalysts (alkaline-earth based-) that are compatible chemically with the state-of-the-art cathode materials at high temperatures required for fabrication and with contaminates commonly encountered under operating conditions; (2) To improve the infiltration process for optimal control of the thickness, composition, and uniformity of the catalyst coatings; (3) To evaluate the electro-catalytic activity toward ORR of the chemically-stable materials when exposed to different types of contaminants using electrical conductivity relaxation measurements on bar samples and performance evaluation of catalyst-infiltrated cathodes; (4) To unravel the contamination-tolerant mechanisms of the new catalyst coatings under realistic environmental conditions (with different types of contaminants) using powerful in situ and in operando characterization techniques performed on model cells with thin-film/pattern electrodes, as guided by modeling and simulation; (5) To establish scientific basis for rational design of new catalysts of high tolerance to contaminants; (6) To validate the long term stability of modified LSCF cathodes in commercially available cells/stacks under ROC. Alkaline earth-based catalysts have been systematically explored and tested under various contamination conditions. BaCoO 3-δ (BCO) was shown to produce the best catalytic activity enhancement as well as stability in a variety of contaminating conditions, including CO 2 and chromium. The microstructural evolution was investigated with SEM, EDS, and Raman spectroscopy, showing the BCO catalyst prevents the formation of insulating SrCrO 4 by forming electrically conductive BaCrO 4 . Electrochemical relaxation measurements determined the BCO catalyst coatings increased the surface diffusion coefficient but did not significantly affect the diffusion coefficient and determined an optimum surface modification layer of 100 nm. A novel Ba 0.9 Co 0.7 Fe 0.2 Nb 0.1 O x (BCFN) catalyst was also shown to have excellent stability in chromium containing atmospheres. A novel surface sol-gel (SSG) surface modification, which offers superior thickness and compositional control, was applied to SOFCs to produce BaO catalyst coatings. SSG BaO coatings were shown to produce conformal coatings on the electrode surface, greatly increasing stability in chromium containing atmospheres. An atomic level mechanistic approach was applied to investigate the stability of PrBa 0.8 Ca 0.2 Co2O 5+δ (PBCC) with respect to a variety of common contaminants, demonstrating thermodynamically its superior stability in CO2 containing atmospheres. Finally, the best catalyst coatings demonstrated in this project, BCO and PBCC, were applied to full cells which demonstrated superior stability for over 300 hours in CO 2 and Cr atmospheres.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
NASA NTRS1974

A study of the effects of solid phase reactions on the thermal degradation and ballistic properties of solid propellants

The thermal stability of perchlorate composite propellants was studied at 135 and 170 C. The experimental efforts were concentrated on determining the importance of heterogeneous oxidizer-fuel reactions in the thermal degradation process. The experimental approach used to elucidate the mechanisms by which the oxidizer fuel composites thermally degrade was divided into two parts: (1) keeping the fuel constant and varying the nature of the oxidizers, and (2) holding the oxidizer constant and varying the fuel components. The fuel component primarily utilized in the first phase was polyethylene. Oxidizers included KClO4, KClO3, NH4ClO4 and NH4ClO4 doped with materials such as chlorate, phosphate and arsenate. In the second phase the oxidizer used was primarily NH4ClO4 while the fuels included saturated and unsaturated polybutadiene prepolymers and a series of bonding agents. Techniques employed in the current study include thermogravimetric measurements, differential thermal analysis, infrared, mass spectrometry, electron microscopy, and appropriate wet chemical analysis.

Schmidt, W. G.↗
DOE OSTI2020

Controllable depolymerization of lignin using carbocatalyst graphene oxide under mild conditions

Many efforts have been devoted to depolymerizing lignin to high-value aromatic monomers. However, a controllable and complete lignin inter-unit bond cleavage remains difficult because of the randomness in lignin structure and low selectivity in catalysis. Herein, we demonstrate that a sole carbocatalyst graphene oxide (GO) can selectively oxidize aryl- and alkyl-hydroxyl groups of lignin without the presence of any additional oxidizers, leading to lignin degradation under mild conditions. The results from lignin dimers, lignin oligomers, and organosolv lignin indicate that the depolymerization is catalyzed via an oxidative mechanism through an enol ether intermediate, a stable intermediate that has been chemically isolated here. Quantum chemistry calculations at the density functional theory level indicate that the phenolic –OH group in lignin facilitates the formation of radical cations and thus prohibits ring opening reactions, leading to the complete conversion of lignin dimers to guaiacol through the enol ether intermediate.

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

Highly reversible oxygen redox in layered compounds enabled by surface polyanions

Oxygen-anion redox in lithium-rich layered oxides can boost the capacity of lithium-ion battery cathodes. However, the over-oxidation of oxygen at highly charged states aggravates irreversible structure changes and deteriorates cycle performance. Here, we investigate the mechanism of surface degradation caused by oxygen oxidation and the kinetics of surface reconstruction. Considering Li 2 MnO 3 , we show through density functional theory calculations that a high energy orbital (lO 2p’ ) at under-coordinated surface oxygen prefers over-oxidation over bulk oxygen, and that surface oxygen release is then kinetically favored during charging. We use a simple strategy of turning under-coordinated surface oxygen into polyanionic (SO 4 ) 2- , and show that these groups stabilize the surface of Li 2 MnO 3 by depressing gas release and side reactions with the electrolyte. Experimental validation on Li 1.2 Ni 0.2 Mn 0.6 O 2 shows that sulfur deposition enhances stability of the cathode with 99.0% capacity remaining (194 mA h g -1 ) after 100 cycles at 1 C. Our work reveals a promising surface treatment to address the instability of highly charged layered cathode materials.

25 ENERGY STORAGE↗
DOE OSTI2020

Biogeochemical reactions and release of iron-bound organic carbon during the redox processes. Final report

Accurate simulation and prediction for reactions of soil organic carbon (OC) under different biogeochemical conditions remain a grand challenge. This project aims to investigate the transformation and degradation of OC under anaerobic and aerobic conditions as well as anaerobic-aerobic transitions, as well as its coupling with reactions for iron (Fe) oxide minerals. We determined that OC can serve as electron shuttle (including pyrogenic OC) and donor for accelerating the reduction of Fe oxide. The presence of OC can inhibit the transformation of poor crystalline Fe oxide (ferrihydrite) to other more crystalline forms. Reduction of Fe oxide can lead to the mobilization of OC, depending on the ratio of OC/Fe. More condensed aromatic OC can be selectively associated with Fe oxide and also resistant to the reduction release, enhancing their stability during the anaerobic reactions. Under aerobic condition, the association with Fe oxide can inhibit the degradation of OC and also its priming effects on the degradation of indigenous soil OC. During an anaerobic-aerobic transition, OC mineralization was inhibited substantially compared to controls incubated only aerobically. Our field measurement in the Arctic region revealed the importance of deep soil temperature in regulating the generation of CO 2 and CH 4 . These results highlighted the importance of redox reactions in controlling the fate and stability of soil OC. For future studies, investigations are required to fill in the knowledge gap regarding the structure and chemical nature of important organic ligands for Fe, accurate quantification of Fe-bound OC in soils, the long-term effects of anaerobic-aerobic transitions on the OC mineralization as well as response of microbial communities to redox transitions.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1985

Laboratory studies of Kapton degradation in an oxygen ion beam

Results are presented from a preliminary laboratory investigation of the degradation of the widely used polyimide Kapton under oxygen ion bombardment. Recent space shuttle flights have shown that Kapton and some other materials exposed to the apparent ram flow of residual atmosphere (at orbital velocity in low Earth orbit) lose mass and change their optical properties. It was hypothesized that these changes are caused by chemical interaction with atomic oxygen, aided by the 5-eV impact energy of atmospheric oxygen atoms in the ram. The reaction rate under O(+) bombardment seemed to be independent of incident energy over a wide range of energies. Although the flux of thermal ions in this experiment was much greater than the accelerated flux, the observed Kapton degradation was limited to the beam area and ram flow direction. This is consistent with an activation energy above the thermal energies but well below the beam energies. The results reproduce well the material loss, optical changes, SEM surface structure, and ram directionality of the samples returned by the shuttle. These factors, along with the lack of degradation under argon ion bombardment, are convincing evidence for ram flow oxidation as the mechanism of degradation.

Ferguson, D. C.↗
DOE OSTI2025

Physical and thermal property changes under uniform oxidation in nuclear graphite

Material property changes of fine- and medium-grain nuclear graphite grades were measured after subjection to uniform oxidation. The cores of high temperature reactors are composed of large nuclear graphite block components. Here, these large core components are designed to provide neutron moderation and reflection, create a large thermal sink to assist in operational control, and form the solid core structure containing the nuclear fuel, coolant channels, and the safety critical channels for control rod insertion. Oxidation is a principle degradation mechanism affecting all aspects of the nuclear graphite component functions. This study addresses the underlying physical property changes of nuclear-graphite components for oxidized mass loss ranges beyond the current recommended ASME code rule limits to ensure structural integrity within the graphite components (a maximum mass loss = 10%).

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Effect of Nanoscale Ce 0.8 Gd 0.2 O 2–δ Infiltrant and Steam Content on Ni–(Y 2 O 3 ) 0.08 (ZrO 2 ) 0.92 Fuel Electrode Degradation during High-Temperature Electrolysis

Studies of Ni–yttria-stabilized zirconia (YSZ) fuel electrode degradation mechanisms in solid oxide electrolysis cells (SOECs) are complicated by the different possible Ni–YSZ microstructures and compositions, and the variations in the H 2 /H 2 O ratio encountered in an electrolysis stack. Here, in this study, we describe a life testing scheme aimed at providing survey results on degradation as a function of the H 2 O–H 2 composition, with life tests carried out at five different steam contents from 90% to 10%. A Ni–YSZ-supported symmetric cell geometry is employed both with and without infiltrated nanoscale gadolinia-doped ceria (GDC). Impedance spectroscopy is utilized to observe changes in electrochemical characteristics during the life test, and a transmission-line-based equivalent circuit is used to model the data. Post-test electrode microstructures were observed. The results suggest that the GDC infiltrant reduces the electrode polarization resistance and provides more stable electrode polarization over a range of conditions.

08 HYDROGEN↗
DOE OSTI2025

Spatial Heterogenous Redox Couples Degradation in Sodium-Ion Battery Cathode Materials and the Mitigation of Voltage Fade by Blocking Oxygen Release

The use of anionic redox has become a new paradigm for improving the energy density of rechargeable batteries, which is essential for improving the market competitiveness of sodium-ion batteries. However, issues such as voltage attenuation and cycling stability degradation persist in layered oxide anion redox cathode materials. Here, in this study, we systematically investigate the classic Na-ion cathode material Na 0.6 Li 0.2 Mn 0.8 O 2 , and the primary causes of voltage decay are identified as the activation of cations and the reduction in anion redox activity. In addition, the activation of cations is closely associated with anion reactions. Through the application of sophisticated multiscale synchrotron absorption spectroscopy and imaging techniques, we have identified a pronounced pattern of spatially dependent degradation in the evolution of redox couples, which is more evident from the material’s surface to its core. With this understanding, we introduced a surface fluorination approach that modulates the local chemical coordination environment. This strategy increases the formation energy of surface oxygen vacancies and locks transition metals oxide state. Consequently, it enables more reversible anionic redox reactions, which block the spatial progression of degradation and mitigates voltage decay.

25 ENERGY STORAGE↗
DOE OSTI2023

Oxidation mechanism in a refractory multiple-principal-element alloy at high temperature

Refractory multiple-principal-element alloys (RMPEAs) are promising structural materials to enable increased power efficiency in high-temperature oxidation environments, but the oxidation behavior and microstructures of the oxides, especially at the beginning of the oxidation, have received limited attention. Here, the oxidation mechanism in an equimolar W-Mo-Ta-Nb-V was investigated at 1300 °C and compared with the equimolar W-Mo-Ta-Nb alloy without V. The oxide scale on WMoTaNbV after 1 min exposure is shown to be composed of a degradation layer at the interface of the alloy/oxide, an initial oxide transition layer, followed by the main phase aggregate oxide layer, and an outermost oxide layer. At the early stage of oxidation, the absorption of oxygen by the RMPEA substrate forms a solid solution. Vanadium accelerates the initial degradation process as it forms VO. The initial oxidation-induced degradation of RMPEA follows a sequence governed by the free energy change accompanied by local element segregation. Liquid V-Mo oxides aggregate in the intermediate oxide layer. The inward growth of the oxide scale is controlled by the local composition changes, the orientation of the substrate, the crystal structure, and physical properties such as melting points of the oxides.

36 MATERIALS SCIENCE↗
NASA NTRS1992

Crack healing behavior of hot pressed silicon nitride due to oxidation

It is shown that limited oxidation of an MgO-containing, hot-pressed silicon nitride ceramic at 800 deg C and above results in increased strength due to crack healing. Slight oxidation of the surface produces enstatite and cristobalite which fills in cracks. More extensive oxidation leads to strength degradation due to the formation of new flaws by the evolution of N2 gas at the surface. The apparent fracture toughness also increased at 800 deg C and above due to oxidation. Bonds formed between the two surfaces of the crack during oxidation leads to a reduction in stress intensity at the crack tip, suggesting that valid high-temperature toughness values cannot be obtained in an air environment. The increase in strength due to crack healing by oxidation can be achieved without compromising the fatigue properties of the silicon nitride ceramic.

Choi, S. R.↗