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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Stress-Activated Positive Holes (O− in a Matrix of O2–) Cause DNA Damage in Surface-Dwelling Organisms: Unveiling Mutation-Induced Secrets of Nature

Peroxy defects consist of pairs of tightly bonded oxygen anions in the –1 valence state such as in O3X/OO\YO3 with X, Y = Si4+, Al3+ etc. They commonly occur in igneous, metamorphic and many sedimentary rocks. When such rocks are stressed by tectonic forces, peroxy defects break up, releasing highly mobile electronic charge carriers: defect electrons in the O2– sublattice, i.e. unbound O–, known as “positive holes”, h•. The h• can flow out of stressed rock volumes, spreading far and wide, causing electric currents and electrochemical reactions. This study explores how the h• impact the electron flow in the electron transport chain (ETC) of organisms on the surface of rocks such as gabbro and granite. We found that, by forming hydroxyl radicals and superoxide anions, the h• disrupt the in vivo coordination of reduction-oxidation reactions that are essential for the timing of the redox cycle. Our observations show that stress activation of h• delays the sprouting of certain plant seeds and impedes the growth of yeast cultures, Saccharomyces cerevisiae. The h• induce mutations and affect plant development as evidenced by reduced stem length and leaf size. At the same time, the h• serve as a source of abiotic oxidation, capable of forming various organic compounds in situ. Through the generation of radical species that create new carbon-carbon bonds the h• facilitate the abiotic synthesis of hydrocarbons and other organic molecules essential to life, including porphyrins. Our findings highlight the intricate interplay between positive holes, redox timing, and biological processes, revealing their significant role in influencing the growth and development of organisms in tectonically stressed crustal environments. Understanding these effects enhances our broader comprehension of redox biology and the influence of environmental factors on cellular development in natural settings.

astrobiology↗
DOE OSTI2023

Chloride Insertion Enhances the Electrochemical Oxidation of Iron Hydroxide Double-Layer Hydroxide into Oxyhydroxide in Alkaline Iron Batteries

Rechargeable alkaline iron batteries that constitute environmentally benign electrolytes and earth-abundant industrial materials are desirable green solutions for large-scale energy storage. As one of the most abundant metal elements in the earth’s crust, iron (Fe) can satisfy nearly all criteria for low-cost and safe battery electrodes. However, challenges in achieving reversible Fe redox impede their extensive implementation in modern energy supply systems. Here, this study revealed that Cl-anion insertion into Fe(OH) 2 layered double hydroxide (LDH) formed a green rust intermediate phase with the formula [Fe 2 2+ Fe 1 3+ (HO – ) 6 ] + [Cl] – , which assisted a high Fe(OH) 2 /FeOOH conversion reaction (64.7%) and improved cycling stability. This new iron redox chemistry was validated by operando X-ray diffraction, electrochemical testing, X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS) analysis, scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy (STEM-EDS) mapping, and molecular dynamics (MD) simulations. Our study provides new insight into designing LDH materials for high-capacity alkaline iron batteries.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Revealing Reaction Pathways of Collective Substituted Iron Fluoride Electrode for Lithium Ion Batteries

Metal fluorides present a high redox potential among the conversion-type compounds, which make them specially work as cathode materials of lithium ion batteries. To mitigate the notorious cycling instability of conversion-type materials, substitutions of anion and cation have been proposed but the role of foreign elements in reaction pathway is not fully evaluated. In this work, we explored the lithiation pathway of a rutile-Fe 0.9 Co 0.1 OF cathode with multimodal analysis, including ex situ and in situ transmission electron microscopy and synchrotron X-ray techniques. Our work revealed a prolonged intercalation–extrusion–cation disordering process during phase transformations from the rutile phase to rocksalt phase, which microscopically corresponds to topotactic rearrangement of Fe/Co–O/F octahedra. During this process, the diffusion channels of lithium transformed from 3D to 2D while the corner-sharing octahedron changed to edge-sharing octahedron. DFT calculations indicate that the Co and O cosubstitution of the Fe 0.9 Co 0.1 OF cathode can improve its structural stability by stabilizing the thermodynamic semistable phases and reducing the thermodynamic potentials. We anticipate that our study will inspire further explorations on untraditional intercalation systems for secondary battery applications.

25 ENERGY STORAGE↗
DOE OSTI2024

Role of Metal–Organic Framework Topology on Thermodynamics of Polyoxometalate Encapsulation

Polyoxometalates (POMs) are discrete anionic clusters whose rich redox properties, strong Brønsted acidity, and high availability of active sites poise them as potent catalysts for oxidation reactions. Here, metal–organic frameworks (MOFs) have emerged as tunable, porous platforms to immobilize POMs, thus increasing their solution stability and catalytic activity. While POM@MOF composite materials have been widely used for a variety of applications, little is known about the thermodynamics of the encapsulation process. Here, we utilize an up-and-coming technique in the field of heterogeneous materials, isothermal titration calorimetry (ITC), to obtain full thermodynamic profiles (ΔH, ΔS, ΔG, K a ) of POM binding. Six different 8-connected hexanuclear Zr-MOFs were investigated to determine the impact of MOF topology (csq, scu, the) on POM encapsulation thermodynamics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Anionic‐Based Layered Oxide Cathodes with High Electrochemical Performance through Dual‐Site Substitutions for Sodium‐Ion Batteries

Mn-rich layered oxide cathodes with anionic redox promise high energy density for sodium-ion batteries (SIBs) due to ultra-high capacity derived from both Mn and O redox couples. Nevertheless, instability of the reactions that lead to poor electrochemical stability hinders the cathodes from practical applications. Here, the Al and Zn dual-site substitution strategy is proposed to enhance electrochemical performance. Here, the designed cathode, Na 0.73 Zn 0.03 Li 0.25 Mn 0.76 Al 0.01 O 2 (AlZn), delivers a high discharge capacity of 242 mAh g −1 with an impressive rate capability (162 mAh g −1 at 1000 mA g −1 ) and excellent capacity retention (89.69% over 150 cycles). In addition, full-cell SIB based on AlZn coupled with hard carbon exhibits a high energy density of 317 Wh kg −1 (based on both cathode and anode mass) and a reasonable capacity retention of 80.8% after 250 cycles. Revealed by advanced investigations, the synergy of robust Al–O in TM layers and O–Zn–O pillars in Na layers helps alleviate severe inactive spinel/rock-salt phase transformation and intragranular cracks in the AlZn cathode. This consequently leads to greatly enhanced electrochemical performance over the pristine cathode. This work provides insight into improving electrochemical properties of anionic-redox-based layered oxides by Al/Zn co-substitutions toward high-energy SIBs.

25 ENERGY STORAGE↗
DOE OSTI2022

An Investigation of the Electrochemical Activity of (Ba/Sr)FeO 3-y Anodes

FeO x , SrFeO 3-y (SF), and Ba 0.5 Sr 0.5 FeO 3–y (BSF) were studied for application as fuel oxidation catalysts in solid oxide fuel cells (SOFC) anodes. Electrodes were prepared by impregnation into porous yttria-stabilized zirconia (YSZ), with La 0.3 Sr 0.7 TiO 3–y (LST) added for electronic conductivity. The electrode impedances decreased dramatically upon addition of SF and BSF and much less when only SrO or FeO x were added. Temperature Programmed Desorption (TPD) of O 2 from oxidized BSF showed O 2 desorbing between 200 °C and 700 °C, while no O 2 desorbed from Fe 2 O 3 below 900 °C. The results, together with thermodynamic analysis, suggest that stabilization of Fe +4 in the perovskite lattice plays an important role in enhancing the catalytic activity of SF and BSF by providing access to a Fe 3+ /Fe 4+ redox couple that can accept oxygen anions from the yttria-stabilized zirconia (YSZ) electrolyte. Oxygen is weakly bound to these sites facilitating its reaction with adsorbed H 2 .

Electrochemistry↗
DOE OSTI2020

Advances in soft X-ray RIXS for studying redox reaction states in batteries

Redox (reduction and oxidation) chemistry provides the fundamental basis for numerous energy-related electrochemical devices. Detecting the electrochemical redox chemistry is pivotal but challenging because it requires independent probes of the cationic and anionic redox states at different electrochemical states. Here, the synchrotron-based soft X-ray mapping of resonant inelastic X-ray scattering (mRIXS) has recently emerged as a powerful tool for exploring such states in electrochemical devices, especially batteries. High-efficiency mRIXS covers the energy range of the absorption edge with the extra dimension of information on the emitted photon energies. In this frontier article, we review recent representative demonstrations of utilizing soft X-ray mRIXS for detecting the novel chemical state during electrochemical operation and for quantifying the cationic redox reactions through inverse partial fluorescence yield analysis (mRIXS-iPFY). More importantly, the non-divalent states of oxygen in electrodes involving oxygen redox reactions could be reliably captured by mRIXS, with its reversibility quantified by the intensity variation of the characteristic mRIXS feature through a super-partial fluorescence yield analysis (mRIXS-sPFY). These recent demonstrations inspire future perspectives on using mRIXS for studying the complex phenomena in energy materials, with both technical and scientific challenges in RIXS theory, in situ/operando experiments, and spatially resolved RIXS imaging.

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

Constructing an Adaptive Heterojunction as a Highly Active Catalyst for the Oxygen Evolution Reaction

Electrochemical water splitting is of prime importance to green energy technology. Particularly, the reaction at the anode side, namely the oxygen evolution reaction (OER), requires a high overpotential associated with O—O bond formation, which dominates the energy-efficiency of the whole process. Activating the anionic redox chemistry of oxygen in metal oxides, which involves the formation of superoxo/peroxo-like (O 2 ) n – , commonly occurs in most highly active catalysts during the OER process. Here, a highly active catalyst is designed: electrochemically delithiated LiNiO 2 , which facilitates the formation of superoxo/peroxo-like (O 2 ) n – species, i.e., NiOO*, for enhancing OER activity. The OER-induced surface reconstruction builds an adaptive heterojunction, where NiOOH grows on delithiated LiNiO 2 (delithiated-LiNiO 2 /NiOOH). At this junction, the lithium vacancies within the delithiated LiNiO 2 optimize the electronic structure of the surface NiOOH to form stable NiOO* species, which enables better OER activity. This finding provides new insight for designing highly active catalysts with stable superoxo-like/peroxo-like (O 2 ) n – for water oxidation.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Photoelectrochemical Nitrate and Nitrite Reduction Using Cu 2 O Photocathodes

Nitrate in wastewater streams causes eutrophication, and nitrate removal is of great importance for environmental protection. Electrochemical nitrate reduction has the advantage of directly converting nitrate to benign or useful chemicals, but it typically requires a considerable overpotential. Here, in this study, photoelectrochemical nitrate reduction is investigated using a Cu 2 O photocathode, where photoexcited electrons in the conduction band inherently have an overpotential of >1.6 V for nitrate reduction. The Cu 2 O photocathode is found to reduce nitrate to nitrite selectively with a high Faradaic efficiency (>85%). More importantly, as the surface of Cu 2 O is particularly catalytic for nitrate reduction, nitrate reduction on Cu 2 O kinetically suppresses photocorrosion of Cu 2 O without the need for additional catalyst or protection layers. In addition to nitrate reduction, nitrite reduction on Cu 2 O is examined to compare the effects of nitrate and nitrite reduction kinetics on the photocurrent generation and photocorrosion of Cu 2 O photocathodes.

25 ENERGY STORAGE↗
DOE OSTI2025

Electrochemical Processes Breaking Strict Phase Electroneutrality in Microemulsions

Phase electroneutrality is a near-omnipresent assumption in electrochemical reactions. Even media such as biphasic oil-water interfaces and kinetically stable emulsions follow this “rule.” This implies all electron transfer reactions must be accompanied by ion transfer to maintain charge balance within a phase. However, due to the small domain size, electroneutrality is known to break down in the electric double layer adjacent to the electrode. Therefore, the appropriateness of the electroneutrality approximation for media with nanoscale domains, such as microemulsions, is questionable. Here, in this work, we show definitively, for the first time, that phase electroneutrality can be violated during an electron transfer reaction in microemulsions. Cyclic voltammograms show that electrochemical oxidation of rubrene is possible in microemulsions when sodium hydroxide is the only supporting electrolyte. Rubrene is a hydrophobic redox compound that is insoluble in water in neutral and radical cation forms, and hydroxide anions are too hydrophilic to transfer to the oil (toluene) phase. Contrary to observations made in emulsion systems, rubrene oxidation in microemulsions seemingly occurs by a mechanism where coupled ion transfer required for rigorous phase electroneutrality is negated. Our results demonstrate that electron transfer reactions within nanometer-sized domains are not subject to restrictions that govern systems with larger domains.

Barth, Brian A. [Univ. of Tennessee, Knoxville, TN↗
DOE OSTI2022

Bulk Oxygen Stabilization via Electrode–Electrolyte Interphase Tailored Surface Activities of Li–Rich Cathodes

The O3-type Li-rich layered oxides (LLOs) are approaching industrial applications as high-energy cathode materials for Li-ion batteries (LIBs), however, they suffer from rapid performance decay associated with oxygen activities. The interplay between surface and bulk transformations in LLOs, especially the electrochemical behaviors of oxygen anions, remains elusive. Here, by regulating the surface of an O3-type LLO (Li 1.13 Mn 0.517 Ni 0.256 Co 0.097 O 2 ) using an all-fluorinated electrolyte, an enhanced capacity retention from 57.4% to 85.3% and a suppressed voltage decay from 1.34 mV cycle –1 to 0.58 mV cycle –1 within 300 cycles are realized. The performance enhancement is attributed to the thin, uniform, robust, and compact F-rich cathode-electrolyte interphase (CEI), which suppresses various types of oxygen-related surface degradation and, more importantly, stabilizes the bulk oxygen reactions. Finally, through the combined experimental and theoretical studies, this work directly reveals the intriguing association between the surface and bulk oxygen activities and demonstrates that optimizing the interphase is an effective approach for improving the stability of high-energy battery cathodes involving oxygen redox reactions.

25 ENERGY STORAGE↗
DOE OSTI2020

Exploring the Charge Compensation Mechanism of P2-Type Na 0.6 Mg 0.3 Mn 0.7 O 2 Cathode Materials for Advanced Sodium-Ion Batteries

P2-type sodium layered transition metal oxides have been intensively investigated as promising cathode materials for sodium-ion batteries (SIBs) by virtue of their high specific capacity and high operating voltage. However, they suffer from problems of voltage decay, capacity fading, and structural deterioration, which hinder their practical application. Therefore, a mechanistic understanding of the cationic/anionic redox activity and capacity fading is indispensable for the further improvement of electrochemical performance. Here, a prototype cathode material of P2-type Na 0.6 Mg 0.3 Mn 0.7 O 2 is comprehensively investigated, which presents both cationic and anionic redox behaviors during the cycling process. By a combination of soft X-ray absorption spectroscopy and electroanalytical methods, we unambiguously reveal that only oxygen redox reaction is involved in the initial charge process, then both oxygen and manganese participate in the charge compensation in the following discharge process. In addition, a gradient distribution of Mn valence state from surface to bulk is disclosed, which could be mainly related to the irreversible oxygen activity during the charge process. Furthermore, we find that the average oxidation state of Mn is reduced upon extended cycles, leading to the noticeable capacity fading. Our results provide deeper insights into the intrinsic cationic/anionic redox mechanism of P2-type materials, which is vital for the rational design and optimization of advanced cathode materials for SIBs.

25 ENERGY STORAGE↗
NASA NTRSDate not supplied

Impact of Stress-Activated Positive Holes on the Redox Timing in Organisms Living at the Surface of Rocks: Unlocking Nature's Secrets

Squeezing and deforming igneous and/or high-grade metamorphic rocks activates electronic charge carriers known as positive holes, h•, that are defect electrons in the O2– sublattice. Similar to h• in semiconductors the h• in rocks affect electrical and thermal properties. They produce electrochemical reactions, localized electrical signals, and currents. In this study, we explore the effects of positive holes on the electron flow in the electron transport chain (ETC) of organisms living at the surface of rocks such as gabbro or granite. We found that positive holes, h•, disrupt the temporal coordination in vivo governed by oscillating reduction-oxidation reactions, known as the redox cycle. Positive holes affect the timing of the redox cycle by interacting with molecules in vivo, leading to the formation of superoxide anions and hydroxyl radicals. Thus, we observed that positive holes significantly impede the growth of yeast Saccharomyces cerevisiae (i.e., colony size) and delay the sprouting of broccoli and chia seeds. Additionally, positive holes were found to exert discernible impacts on plant development such as stem length and leaf size. Our findings highlight the intricate interplay between positive holes, redox timing, and biological processes, shedding light on the potentially significant role of positive holes in influencing the growth and development of organisms in tectonically stressed rock environments. Understanding these effects has implications for a broader understanding of redox biology and of how environmental factors can influence cellular development in natural settings.

Redox Timing in Organisms↗
NASA NTRSDate not supplied

Impact of Stress-Activated Positive Holes on the Redox Timing in Organisms Living at the Surface of Rocks: Unlocking Nature's Secrets

Stressing and deforming igneous and/or high-grade metamorphic rocks activates electronic charge carriers known as positive holes, h•, that are defect electrons in the O2–sublattice, e.g. O-states. Like h•in semiconductors, the h•in rocks affect electrical and thermal properties. They produce electrochemical reactions, localized electrical signals, and currents. In this study, we explore the effects of positive holes on the electron flow in the electron transport chain (ETC) of organisms living at the surface of rocks such as gabbro or granite. We found that positive holes, h•, disrupt the in vivotemporal coordination governed by oscillating reduction-oxidation reactions, known as the redox cycle. Positive holes affect the timing of the redox cycle by interacting with essentialmolecules in vivo, leading to the formation of hydroxyl radicals and superoxide anions. We observed that positive holes significantly impede the growth of yeast Saccharomyces cerevisiae(i.e., colony size) and delay the sprouting of broccoli seeds. Additionally, positive holes were found to exert discernible impacts on plant development such as stem length and leaf size. Our findings highlight the intricate interplay between positive holes, redox timing, and biological processes, shedding light on the potentially significant role of positive holes in influencing the growth and development of organisms in tectonically stressed crustal environments. Understanding these effects has implications for a broader understanding of redox biology and of how environmental factors can influence cellular development in natural settings.

hypermutation↗
DOE OSTI2020

Systematic Study of Different Anion Doping on the Electrochemical Performance of Cobalt-Free Lithium–Manganese-Rich Layered Cathode

Regardless of the appealingly high energy density (1000 Wh kg –1 ) of the lithium–manganese-rich layered oxide cathode (LMR-NMO), this material still suffers from rapid capacity and voltage decay after continuous cycling. LMR-NMO involves the redox reaction of both transition metals and oxygen to gain additional capacity in comparison with a conventional NMC cathode. Due to the use of a high voltage range (beyond 4.4 V), the oxygen release from the structure initiates and in turn generates intergranular cracks and spinel formation, consequently, into rock-salt structure. Here, LMR-NMO with different doping ranges (1–5 mol %) of F, S, and Cl are being examined to summarize the benefits and drawbacks of each anion. This study shows that F is the best candidate as it increases average voltage (voltage retention 96–97% after 200 cycles at 0.5 C), improves ionic conductivity (nearly two times higher than pristine), reduces cation mixing, minimizes oxygen release, and offers high stability during high temperature cycle. However, for S and Cl, the results are conflicted. An optimal amount of anion dopants should be considered as the side effects might overcome the benefits when the doping amount is excessive.

25 ENERGY STORAGE↗
DOE OSTI2020

Structures and Free Energies of Cerium Ions in Acidic Electrolytes

The Ce 3+ /Ce 4+ redox potential changes with the electrolyte, which could be due to unequal anion complexation free energies between Ce 3+ and Ce 4+ or a change in the solvent electrostatic screening. Ce complexation with anions and solvent screening also affect the solubility of Ce and charge transfer kinetics for electrochemical reactions involving waste remediation and energy storage. Here, we report the structures and free energies of cerium complexes n seven acidic electrolytes based on Extended X-ray Absorption Fine Structure, LTV vis, and Density Functional Theory calculations. Ce 3+ coordinates with nine water molecules as [Ce(H 2 O) 9 ] 3+ in all studied electrolytes. However, Ce 4+ complexes with anions in all electrolytes except HClO 4 . Thus, our results suggest that Ce 4+ anion complexation leads to the large shifts in standard redox potential. Long range screening effects are smaller than the anion complexation energies but could be responsible for changes in the Ce solubility with acid.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗