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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
DOE OSTI2021

Characterization of cellular oxidative stress response by stoichiometric redox proteomics

The thiol redox proteome refers to all proteins whose cysteine thiols are subjected to various redox-dependent posttranslational modifications (PTMs) including S-glutathionylation (SSG), S-nitrosylation (SNO), S-sulfenylation (SOH), and S-sulfhydration (SSH). These modifications can impact various aspects of protein function, including activity, binding, conformation, localization, and interactions with other molecules. It is highly desirable to have robust redox proteomics methods that can provide global, site-specific, and stoichiometric quantification of redox PTMs in order to elucidate the complex redox landscape and identify novel redox regulators in signaling and regulation. Mass spectrometry-based redox proteomics has emerged as the primary platform for enabling the broad characterization of thiol PTMs in cells and tissues. Herein we review recent advances in MS-based redox proteomics approaches for quantitative profiling of redox PTMs in cells and tissues at physiological or oxidative stress conditions and highlight some recent applications using these enabling techniques. Considering the relative maturity of available methods, a primary emphasis will be on two types of modifications: 1) total oxidation (i.e., all reversible thiol modifications), the level of which represents the overall redox state, and 2) S-glutathionylation, a major form of reversible thiol oxidation. We also discuss the significance of stoichiometric measurements of thiol PTMs as well as future perspectives towards a better understanding of cellular redox regulatory networks in cells and tissues.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Mechanistic Insights on Permeation of Water over Iron Cations in Nanoporous Silicon Oxide Films for Selective H 2 and O 2 Evolution

Electrocatalysts encapsulated by an ultrathin and semipermeable oxide layer offer a promising avenue for efficient, selective, and cost-effective production of hydrogen through photoelectrochemical water splitting. This architecture is especially attractive for Z-scheme water splitting, for which a nanoporous oxide film can be leveraged to mitigate undesired, yet kinetically facile, reactions involving redox shuttles, such as aqueous iron cations, by limiting transport of these species to catalytically active sites. In this work, molecular dynamics simulations were combined with electrochemical measurements to provide a mechanistic understanding of permeation of water and Fe(III)/Fe(II) redox shuttles through nanoporous SiO 2 films. It is shown that even for SiO 2 pores with a width as small as 0.8 nm, water does not experience any energy barrier for permeating into the pores due to a favorable interaction with hydrophilic silanol groups on the oxide surface. In contrast, permeation of Fe(III) and Fe(II) into microporous SiO 2 pores is limited due to high energy barriers, which stem from a combination of distortion and dehydration of the second and third ion solvation shells. Furthermore, our simulations and experimental results show that SiO 2 coatings can effectively mitigate undesired Fe(III)/Fe(II) redox reactions at underlying electrodes by attenuating permeation of iron cations, while allowing water to permeate and thus participate in water splitting reactions. In a broader context, our study demonstrates that selectivity of solvated cations can be manipulated by controlling the pore size and surface chemistry of oxide films.

14 SOLAR ENERGY↗
DOE OSTI2024

Facile Interfacial Reduction Suppresses Redox Chemical Expansion and Promotes the Polaronic to Ionic Transition in Mixed Conducting (Pr,Ce)O 2−δ Nanoparticles

Mixed ionic/electronic conductors (MIECs) are essential components of solid-state electrochemical devices, such as solid oxide fuel/electrolysis cells. For efficient performance, MIECs are typically nanostructured, to enhance the reaction kinetics. However, the effect of nanostructuring on MIEC chemo-mechanical coupling and transport properties, which also impact cell durability and efficiency, has not yet been well understood. Here, in this work, Pr 0.2 Ce 0.8 O 2−δ (PCO20) nanopowders were prepared by coprecipitation, then sintered in a modified dilatometer at three different temperatures (600, 725, and 850 °C) for microstructure evolution, resulting in three samples with different average particle sizes (23, 30, and 53 nm). The chemical strain and electronic/ionic conductivity were then measured simultaneously on stable nanostructures in four isotherms from 550 to 400 °C with steps in pO 2 (1 to 10 –4 atm O 2 ). A microcrystalline bar was prepared and measured for comparison. Particle size reduction led to a monotonically decreasing isothermal redox chemical strain, confirmed by in situ high-temperature, controlled-atmosphere XRD measurements. The corresponding conductivity measurements provided defect chemical insight into the particle size-dependent chemical expansion behavior. The significant weakening of the pO 2 dependence and decreased activation energy for electrical conduction with decreasing particle size indicated a decrease in the reduction enthalpy of PCO, shifting the transition from (Pr) polaronic to ionic behavior to higher pO 2 . STEM-EELS measurements confirmed the majority of Pr was reduced to 3+ in the nanoparticles, while Ce remained 4+. These results demonstrate suppression of deleterious chemical expansion and tailoring of the dominant charge carrier simply through controlling the particle size, providing insights for MIEC microstructural design.

ceria↗
DOE OSTI2020

Thaw Transitions and Redox Conditions Drive Methane Oxidation in a Permafrost Peatland

Thawing permafrost, ground that has been frozen for 2 or more years, often results in wet conditions that promote the production of methane (CH 4 ). Methane is a greenhouse gas that is over 30 times more powerful than carbon dioxide at warming the atmosphere. Microorganisms called methanotrophs can consume a substantial portion of this CH 4 before it reaches the atmosphere, but the extent of this consumption is not well understood. Methanotrophs are affected by environmental conditions, such as oxygen availability, that change with permafrost thaw. We used laboratory experiments to measure how quickly methanotrophs consume CH 4 from sites within a permafrost peatland with little, intermediate, and full permafrost thaw. We found that CH 4 consumption increased as permafrost thawed and that sites transitioning between thaw stages had a different potential to consume CH 4 than intact and fully thawed sites. Methane consumption was also high in locations with low dissolved oxygen, which suggests that methanotrophs in these sites may tolerate low oxygen conditions in the field. We found that redox potential, a measurement that describes the tendency for a compound to be oxidized or reduced, was a strong predictor of CH 4 consumption in partially and fully thawed sites. Overall, these measurements highlight the potential for methanotrophs to mitigate CH 4 emissions in peatlands with thawing permafrost and provide new insights to modeling CH 4 dynamics across the full thaw gradient.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

In situ beam reduction of Pu(IV) and Bk(IV) as a route to trivalent transuranic coordination complexes with hydroxypyridinone chelators

The solution-state interactions of plutonium and berkelium with the octadentate chelator 3,4,3-LI(1,2-HOPO) (343-HOPO) were investigated and characterized by X-ray absorption spectroscopy, which revealed in situ reductive decomposition of the tetravalent species of both actinide metals to yield Pu(III) and Bk(III) coordination complexes. X-ray absorption near-edge structure (XANES) measurements were the first indication of in situ synchrotron redox chemistry as the Pu threshold and white-line position energies for Pu-343-HOPO were in good agreement with known diagnostic Pu(III) species, whereas Bk-343-HOPO results were found to mirror the XANES behavior of Bk(III)-DTPA. Extended X-ray absorption fine structure results revealed An—O HOPO bond distances of 2.498 (5) and 2.415 (2) Å for Pu and Bk, respectively, which match well with bond distances obtained for trivalent actinides and 343-HOPO via density functional theory calculations. Pu(III)- and Bk(III)-343-HOPO data also provide initial insight into actinide periodicity as they can be compared with previous results with Am(III)-, Cm(III)-, Cf(III)-, and Es(III)-343-HOPO, which indicate there is likely an increase in 5 f covalency and heterogeneity across the actinide series.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Crossover Flux and Ionic Resistance Metrics in Polysulfide-Permanganate Redox Flow Battery Membranes

A survey of 23 commercially available cation exchange membranes was performed for the downselection of membranes for use in a polysulfide-permanganate redox flow battery (pS-Mn RFB). The survey measured the flux of permanganate ions across a 0.1 mol L −1 concentration gradient as well as the membrane resistance in a 0.5 mol L −1 sodium chloride solution. The membranes exhibited the characteristic flux/resistance trade-off observed in most classes of membranes. To connect the individual membrane testing to how the membranes will perform in a device, cell performance data in a pS-Mn RFB was collected for three membranes from the survey. The coulombic, voltaic, and energy efficiency at low cycle counts aligned with the predictions from the membrane flux and resistance survey results. The study also identified three membranes—Fumapem F-930-RFS, Fumapem FS-715-RFS, and Aquivion E98-09S—that outperformed most other membranes regarding their position on the flux-resistance trade-off curve, indicating them to be good candidates for further testing.

Electrochemistry↗
DOE OSTI2024

Partitioning of Fe(II) in reduced nontronite (NAu-2) to reactive sites: Reactivity in terms of Tc(VII) reduction

Abstract Clay minerals impart important chemical properties to soils, in part, by virtue of changes in the redox state of Fe in their crystal structures. Therefore, measurement of Fe(III)/Fe(II) and partitioning of Fe(II) in different reactive sites in clay minerals (during biological and chemical Fe(III) reduction) is essential to understand their role and their relative reactivity in terms of reduction and immobilization of heavy metal contaminants such as technetium. This study had three objectives: (1) to understand the degree of dissolution of nontronite (Fe-rich smectite) as a result of chemical and biological reduction of Fe(III) in the structure; (2) to quantify partitioning of chemically and biologically produced Fe(II) into different reactive sites in reduced nontronite, including aqueous Fe 2+ , ammonium chloride-extractable Fe(II) (mainly from the ion-exchangeable sites, denoted as Fe ( II ) NH 4 Cl ${\rm{Fe}}{\left( {{\rm{II}}} \right)_{{\rm{N}}{{\rm{H}}_4}{\rm{Cl}}}}$ ), sodium acetate-extractable Fe(II) (mainly from the surface complexation sites, denoted as Fe(II) acetate ), and structural Fe(II) (denoted as Fe(II) str ); and (3) to evaluate the reactivity of these Fe(II) species in terms of Tc(VII) reduction. Chemical and biological reduction of Fe(III) in nontronite (NAu-2) was performed, and reduced nontronite samples with different extents of Fe(III) reduction (1.2–71%) were prepared. The extent of reductive dissolution was measured as a function of the extent of Fe(III) reduction. Our results demonstrated that chemically and biologically produced Fe(II) in NAu-2 may be accommodated in the NAu-2 structure if the extent of Fe(III) reduction is small (< ∼30%). When the extent of reduction was >∼30%, dissolution of nontronite occurred with a corresponding decrease in crystallinity of residual nontronite. The Fe(II) produced was available for partitioning into four species: Fe ( ab ) 2 + ${\rm{Fe}}_{\left( {{\rm{ab}}} \right)}^{2 + }$ , Fe(II) acetate , Fe ( II ) NH 4 Cl ${\rm{Fe}}{\left( {{\rm{II}}} \right)_{{\rm{N}}{{\rm{H}}_4}{\rm{Cl}}}}$ , and Fe(II) str . The increase in Fe(II) acetate during the early stages of Fe(III) reduction indicated that the Fe(II) released had the greatest affinity for the surface-complexation sites, but this site had a limited capacity (∼60 µmol of Fe(II)/g of NAu-2). The subsequent increase in Fe ( II ) NH 4 Cl ${\rm{Fe}}{\left( {{\rm{II}}} \right)_{{\rm{N}}{{\rm{H}}_4}{\rm{Cl}}}}$ indicated that the released Fe(II) partitioned into the exchangeable sites once the amount of Fe at the surface-complexation sites reached half of its maximum site capacity. The fraction of Fe(II) str decreased concomitantly, as a result of Fe(II) release from the NAu-2 structure, from 100% when the extent of Fe(III) reduction was <30% to nearly 65% when the extent of Fe(III) reduction reached 71%. The Fe(II) acetate and Fe(II) str exhibited greater reactivity in terms of Tc(VII) reduction than the Fe ( II ) NH 4 Cl ${\rm{Fe}}{\left( {{\rm{II}}} \right)_{{\rm{N}}{{\rm{H}}_4}{\rm{Cl}}}}$ . Clearly, the surface-complexed and structural Fe(II) are the desirable species when reduced clay minerals are used to reduce and immobilize soluble heavy metals in contaminated groundwater and soils. These results have important implications for understanding microbe—clay mineral interactions and heavy metal immobilization in clay-rich natural environments.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Eu speciation in apatite at 1 bar: An experimental study of valence-state partitioning by XANES, lattice strain, and Eu/Eu* in basaltic systems

Abstract Partition coefficients for rare earth elements (REEs) between apatite and basaltic melt were determined as a function of oxygen fugacity (fO2; iron-wüstite to hematite-magnetite buffers) at 1 bar and between 1110 and 1175 °C. Apatite-melt partitioning data for REE3+ (La, Sm, Gd, Lu) show near constant values at all experimental conditions, while bulk Eu becomes more incompatible (with an increasing negative anomaly) with decreasing fO2. Experiments define three apatite calibrations that can theoretically be used as redox sensors. The first, a XANES calibration that directly measures Eu valence in apatite, requires saturation at similar temperature-composition conditions to experiments and is defined by: ( E u 3 + ∑ E u ) Apatite = 1 1 + 10 - 0.10 ± 0.01 × l o g ⁡ ( f o 2 ) - 1.63 ± 0.16 . The second technique involves analysis of Sm, Eu, and Gd in both apatite and coexisting basaltic melt (glass), and is defined by: ( Eu E u * ) D Sm × Gd = 1 1 + 10 - 0.15 ± 0.03 × l o g ⁡ ( f o 2 ) - 2.46 ± 0.41 . The third technique is based on the lattice strain model and also requires analysis of REE in both apatite and basalt. This calibration is defined by ( Eu E u * ) D lattice strain = 1 1 + 10 - 0.20 ± 0.03 × l o g ⁡ ( f o 2 ) - 3.03 ± 0.42 . The Eu valence-state partitioning techniques based on (Sm×Gd) and lattice strain are virtually indistinguishable, such that either methodology is valid. Application of any of these calibrations is best carried out in systems where both apatite and coexisting glass are present and in direct contact with one another. In holocrystalline rocks, whole rock analyses can be used as a guide to melt composition, but considerations and corrections must be made to either the lattice strain or Sm×Gd techniques to ensure that the effect of plagioclase crystallization either prior to or during apatite growth can be removed. Similarly, if the melt source has an inherited either a positive or negative Eu anomaly, appropriate corrections must also be made to lattice strain or Sm×Gd techniques that are based on whole rock analyses. This being the case, if apatite is primary and saturates from the parent melt early during the crystallization sequence, these corrections may be minimal. The partition coefficients for the REE between apatite and melt range from a maximum DEu3+ = 1.67 ± 0.25 (as determined by lattice strain) to DLu3+ = 0.69 ± 0.10. The REE partition coefficient pattern, as observed in the Onuma diagram, is in a fortuitous situation where the most compatible REE (Eu3+) is also the polyvalent element used to monitor fO2. These experiments provide a quantitative means of assessing Eu anomalies in apatite and how they be used to constrain the oxygen fugacity of silicate melts.

Geochemistry & Geophysics↗
DOE OSTI2022

High Performance Circuit Pastes for Solid Oxide Fuel Cell Applications: Final Technical Report

Using a combination of in-plane electrical conductivity measurements, electrical contact resistance measurements, tensile fracture tests, double shear lap fracture tests, rapid thermal cycling adhesion tests, in situ wetting angle measurements, 3D X-ray tomography, reduction-oxidation (RedOx) cycling, scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDAX), Density Functional Theory (DFT) modeling, Molecular Dynamics (MD) modeling, and Phase Field modeling, this project determined that a new brazing technique developed by the PIs (specifically the use of nickel particles to direct the wetting and spreading of molten silver) could be used to produce well-adhered, >97% dense, electrically-conductive circuits, current collectors, and/or electrical contacts on a variety of ceramic and ceramic-coated substrates (specifically lanthanum strontium manganite, yttria stabilized zirconia, sapphire, Cr2O3-passivated stainless steel, and Al2O3-passivated stainless steel). Compared to other silver-based alternatives, Ag:Ni led to less manufacturing defects and was more tolerant of the extreme environments (isothermal high-temperature aging) and occasional abuse (rapid thermal cycling and RedOx cycling) encountered during Solid Oxide Fuel Cell and/or Solid Oxide Electrolysis Cell operation. Further, in some situations (such as when to produce Ag:Ni electrical contacts to Al2O3-protected stainless steel) the Ni particles also improved operation by acting as chemical getters that removed electrically-insulating, surface-segregating substrate impurities (i.e. by lowering the contact resistance with the underlying substrate).

36 MATERIALS SCIENCE↗
DOE OSTI2025

Redox conduction facilitates direct interspecies electron transport in anaerobic methanotrophic consortia

Anaerobic methanotrophic archaea (ANME) and sulfate-reducing bacteria (SRB) form syntrophic partnerships in marine sediments to consume greenhouse gas methane. While direct interspecies electron transport is proposed to enable ANME/SRB symbiosis, its electrochemical properties remain uncharacterized. Here, using sediment-free enrichment cultures, we measured the electron transport capabilities of marine consortia under physiological conditions. Diverse ANME/SRB consortia exhibited high dry conductance close to electrogenic biofilms. This conductance diminished upon exposure to heat or oxygen but was preserved following paraformaldehyde fixation, indicating a biomolecular origin for this electric charge transfer. Cyclic voltammetry revealed redox activity centered at 28 ± 11, 94 ± 6, and 24 ± 7 millivolts for ANME-1/Desulfofervidus, ANME-2a/Seep-SRB1, and ANME-2a+2c/Seep-SRB1+2 consortia, respectively. Generator-collector measurements further demonstrated that these redox components facilitate electron transport over micrometer-scale distances, sufficient to link archaeal and bacterial partners. Collectively, our results establish that marine ANME/SRB symbiosis uses redox conduction, consistent with multiheme cytochromec, for direct interspecies electron transport.

Science & Technology - Other Topics↗
DOE OSTI2020

Boosting energy efficiency of Li-rich layered oxide cathodes by tuning oxygen redox kinetics and reversibility

In developing electrode materials for next-generation Li-ion batteries, significant efforts have been given to the energy, power density and cycling stability, with much less (if any) attention paid to the energy efficiency – arguably, the most important practical measure for large-scale applications. This is particularly true for the oxygen-redox active electrodes, such as Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 , the notorious energy-inefficient cathode that has an extremely high capacity but comes with large voltage hysteresis and voltage decay. Herein, we report the rational design of an energy-efficient Li-rich layered cathode along with high energy, power density and cycling stability enabled by tuning oxygen redox activity. Specifically, the target material Li 1.12 Ni 0.22 Co 0.13 Mn 0.52 O 2 exhibits an ultrahigh energy efficiency at 1 C (90.6%), high capacity (> 200 mAh g -1 ) with 98.9% retention and less than 150 mV decay at the extended 200 cycles. Overall, through direct comparison between the material and Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 , we show that the compositional change, although slightly, greatly improves the oxygen redox kinetics and reversibility, thereby boosts energy efficiency. The findings offer a strategy to narrow the gap between scientific interest and practical application of oxygen-redox chemistry.

36 MATERIALS SCIENCE↗
DOE OSTI2020

A Comparative Study of Redox Mediators for Improved Performance of Li-Oxygen Batteries.

Redox meditators (RMs) are soluble catalysts located in an electrolyte that can improve the energy efficiency (reduced overpotential) and cyclability of Li-oxygen (Li-O-2) batteries. In this work, 20 RMs within a Li-O-2 system with dimethyl sulfoxide and tetraethylene glycol dimethyl ether electrolytes are studied and their electrochemical features such as redox potential, the separation of cathodic and anodic peaks, and their current intensities are measured using cyclic voltammetry (CV) experiments. Six RMs are selected as "primary" choices based on their electrochemical performance, and stability tests are then performed to examine their electrochemical responses after consecutive cycles. Moreover, galvanostatic cycling tests are performed within a Li-O-2 battery system assembled with selected six RMs for real case consistency investigations. It is found that results from CV to galvanostatic cycling tests are consistent for halides and organometallic RMs, where the former exhibit much higher stability. However, the organic RMs show high reversibility in CV but low in battery cycling results. Density functional theory calculations are carried out to gain more understanding of the stability and redox potentials of the RMs. This study provides comparative information to select the most reliable RMs for Li-O-2 batteries along with new fundamental understanding of their electrochemical activity and stability.

cyclic voltammetry↗
DOE OSTI2020

Iodine Co-Precipitation with Calcium Carbonate in the Presence of Silica Ions - 20360

Historical releases of I-129 to the subsurface at the U.S. Department of Energy Hanford Site have resulted in large dilute plumes that cover an area of over 50 km{sup 2}. The most concentrated I-129 plume is associated with the 200 West Area in the 200-UP-1 operable unit of the Hanford Central Plateau, where peak concentrations have been measured up to 30 times the drinking water standard of 1 pCi/L. The mobility of iodine depends on many factors, including chemical speciation, pH, redox conditions, as well as the presence of organic matter, calcium carbonate minerals and microbial activities. Speciation measurements estimate that the majority of the iodine (∼76%) in Hanford groundwater exists as iodate. Information on processes that affect iodate mobility in the Hanford subsurface support evaluation of environmental management options for the I-129 plumes. Iodate can be incorporated into calcium carbonate, which is a potential mechanism of naturally attenuating radioiodine in groundwater. However, the silica content in porewater may impact the contaminant-calcium carbonate incorporation process. Silica is one of the most abundant elements in nature and can have an impact on chemical weathering of alkaline-earth carbonates in the environment. Hence, this research aims to advances knowledge of the iodine co-precipitation process with calcium carbonate in the presence of silica. This information supports the technical basis evaluation of natural attenuation for I-129. Samples for these studies were prepared using calcium carbonate-forming solutions that included certified grade sodium meta-silicate nonahydrate (Na{sub 2}SiO{sub 3}), calcium chloride dehydrate (CaCl{sub 2}.2H{sub 2}O), sodium carbonate (NaCO{sub 2}), and sodium hydroxide (NaOH) solutions for pH adjustments. Triplicate samples were prepared with silica concentrations in the solution of 0 mM, 0.5 mM and 20 mM, mixed with an iodate standard (1000 ppm of IO{sub 3}{sup -} in H{sub 2}O) and sampled over a one-week period. Preliminary data analyses suggest that less iodine remains in solution in the presence of silica (average remaining aqueous fraction 0.23±0.03 at 20 mM of Si) relative to samples without silica (0.52±0.06); an indication that more iodine has been sorbed or incorporated into precipitates. However, the mechanisms for this behavior are still under investigation and need to be interpreted relative to pore water compositions that are representative of Hanford site-specific conditions. Scanning electron microscope equipped with energy dispersive spectroscopy (SEM-EDS) analyses were performed to observe the solid phase morphology in these experiments and showed rhombohedral calcite crystals covered with amorphous Si floccules. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2021

Six–Electron Chemistry of a Binuclear Fe(III) Fused Porphyrin

Here in this special collection dedicated to Prof. Jean-Michel Savéant, we report on the synthesis and characterization of a novel binuclear Fe(III) fused porphyrin. Ultraviolet-visible spectroscopy confirms the extended electronic structure of this macrocycle. In addition, Fourier transform infrared spectroscopy indicates the Fe centers experience a relatively rigid ligand environment as compared to a structurally related mononuclear complex featuring an 18 π-aromatic porphyrin ligand. X-ray photoelectron and X-ray absorption near edge spectroscopies confirm the iron centers of both assemblies are Fe(III) in the as prepared, resting state. In comparison with the mononuclear porphyrin, electrochemical measurements show there is a doubling of the number of redox events associated with the fused, binuclear complex. In conclusion, key features of the fused-iron-porphyrin include: 1) bimetallic-iron sites, 2) a π-extended ligand capable of delocalizing electrons across the multimetallic scaffold, and 3) the ability to store up to six electrons.

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

The Quest for Functional Oxide Cathodes for Magnesium Batteries: A Critical Perspective

The Mg battery is an energy storage technology which has garnered significant interest in recent years. Mg batteries incorporating a metal oxide cathode (MOC) are potential candidates to supersede the state-of-the-art Li-ion battery in energy density, cost, and sustainability. However, there are significant discrepancies in reported performances and reactivities of Mg battery MOCs, with detailed analyses revealing that parasitic electrolyte reactions can contribute almost entirely to the measured capacity. This Perspective describes a holistic approach. encompassing elemental, redox, and structural probes-which is vital to robustly confirm and quantify Mg intercalation in MOCs. It critically surveys recent literature for applications of this approach to reveal true state-of-the-art MOCs for Mg batteries. We also suggest testing and analysis protocols to ensure fair comparison of future reports with these state-of-the-art materials.

25 ENERGY STORAGE↗
DOE OSTI2022

Elucidating Cathode Degradation Mechanisms in LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811)/Graphite Cells Under Fast Charge Rates Using Operando Synchrotron Characterization

Li-ion batteries capable of extreme fast charging (XFC) are in demand to facilitate widespread electric vehicle (EV) adoption. While the impact of fast charge on the negative electrode has been studied, degradation of state-of-the-art NMC811 under XFC conditions has not been studied in detail. Herein, cathode degradation is probed in NMC811/graphite batteries by analysis of structural and chemical changes for recovered samples previously cycled under XFC conditions and during typical cycling. NMC surface reconstruction, as determined by soft X-ray absorption, was not detected for recovered electrodes. Furthermore, bulk redox activity from X-ray absorption near edge structure measurements showed more change in the oxidation state of Ni and Co under the 1C charge rate compared to the 4C rate consistent with the electrochemistry. Increased unit cell volume contraction under the 1C rate as determined by operando X-ray diffraction suggests that higher charge rates may provide a protective effect on the cathode by reducing structural distortion due to less delithiation.

25 ENERGY STORAGE↗
DOE OSTI2024

Understanding and modeling current and future coastal wetland methane dynamics (Final Report)

The coastal terrestrial-aquatic interface (TAI) is a highly dynamic component of the Earth system that plays a critical role in biogeochemical cycling. Due to its dynamic nature, the processes that regulate decomposition and methane (CH 4 ) emissions are of greater significance at the TAI than in upland systems. Despite this, we have limited mechanistic understanding of how climate stressors interact to regulate the electron acceptors and donors that determine decomposition pathways within TAIs, including the generation of hot spots and hot moments. Accurately modeling these processes is critical for incorporating the coastal TAI into Earth systems models, such as DOE’s E3SM. With previous DOE support, we adapted an aerobic terrestrial representation of decomposition using PFLOTRAN, a reactive flow and transport model, and added anerobic decomposition pathways, salinity, and oxygen (O 2 ) that fluctuates independently of water table level. However, because this model (PFLOTRAN TAI ) is based on decomposition rates and organic matter carbon to nitrogen ratios from terrestrial systems, its performance in TAI systems is currently limited by the lack of empirical data to properly parameterize variables. In addition, while PFLOTRAN TAI can simulate movement of O 2 into sediments, it is not currently capable of tracking the movement of CH 4 gas through plant tissues due to both current model structure and lack of available data. Our overall objective of the project was the increase our mechanistic understanding of CH 4 dynamics in response to environmental change, such that we can improve the representation of these dynamics in PFLOTRAN. We installed automated flux chambers in a new field-scale active soil warming experiment and set up marsh organs (mesocosms) to test effects of warming, flooding, and salinity. This resulted in a new dataset consisting of chamber-level CH 4 flux measurements across multiple sites, ecological conditions, and timeframes, as well as corresponding measurements on porewater chemistry, soil carbon quality, plant biomass, and redox reaction rates. Using these data, we improved PFLOTRAN TAI to more accurately model CH 4 dynamics and successfully tested our hypotheses. This grant contributed to the professional development of 3 postdocs, 4 undergraduate interns, 4 teacher interns, 17 technicians, and 15 participatory scientists. The automated chamber technology designed for this grant has also been shared with multiple new projects.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2026

Development of Composite Photocatalyst Materials that are Highly Selective for Solar Hydrogen Production and their Evaluation in Z-Scheme Reactor Designs

The key technology gap preventing a vertically stacked dual-bed particle suspension reactor from achieving the DOE MYRD&D ultimate cost target for H 2 production remains the lack of materials in particle form factor that exhibit ≥10% solar-to-H 2 energy conversion (STH) efficiency as a suspension. Therefore, our project goals centered around strategies to increase the STH efficiency by enhancing photophysical properties of perovskite oxide particles including increased visible-light absorption, increased selectivity for electrocatalysis of the H 2 evolution reaction (HER) and the O 2 evolution reaction (OER) through development of ultrathin oxide coatings, correlating composition and structure to function, and improving understanding of multiscale transport and kinetic processes.

08 HYDROGEN↗