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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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125 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Extended Interfacial Stability through Simple Acid Rinsing in a Li-Rich Oxide Cathode Material

Layered Li-rich Ni, Mn, Co (NMC) oxide cathodes in Li-ion batteries provide high specific capacities (>250 mAh/g) via O-redox at high voltages. However, associated high-voltage interfacial degradation processes require strategies for effective electrode surface passivation. Here, we show that an acidic surface treatment of a Li-rich NMC layered oxide cathode material leads to a substantial suppression of CO 2 and O 2 evolution, ~90% and ~100% respectively, during the first charge up to 4.8 V vs. Li +/0 . CO 2 suppression is related to Li 2 CO 3 removal as well as effective surface passivation against electrolyte degradation. This treatment does not result in any loss of discharge capacity and provides superior long-term cycling and rate performance compared to as-received, untreated materials. We also quantify the extent of lattice oxygen participation in charge compensation (“O-redox”) during Li + removal by a novel ex-situ acid titration. Our results indicate that the peroxo-like species resulting from O-redox originate on the surface at least 300 mV earlier than the activation plateau region around 4.5 V. X-ray photoelectron spectra and Mn -L X-ray absorption spectra of the cathode powders reveal a Li + deficiency and a partial reduction of Mn ions on the surface of the acid-treated material. More interestingly, although the irreversible oxygen evolution is greatly suppressed through the surface treatment, our O K-edge resonant inelastic X-ray scattering shows the lattice O-redox behavior largely sustained. The acidic treatment, therefore, only optimizes the surface of the Li-rich material and almost eliminates the irreversible gas evolution, leading to improved cycling and rate performance. This work therefore presents a simple yet effective approach to passivate cathode surfaces against interfacial instabilities during high-voltage battery operation.

25 ENERGY STORAGE↗
DOE OSTI2024

Catalytic Reduction of Carbon Monoxide to Liquid Fuels with Recyclable Hydride Donors

Solar light absorption and catalysis are physically separated processes in natural photosynthesis. Natural cofactors, such as nicotinamide adenine dinucleotides (NADH), transport electrons and hydrogen to regulate and activate enzymes at remote locations. The physical separation of light absorption from catalysis provides some inspiration for artificial photosynthesis. One rather extreme implementation is to use copper wires to transport carriers from photovoltaic cells to dark electrodes, where catalysis occurs. Indeed, with a futuristic electrical grid powered solely by photovoltaics, solar capture could be separated from catalysis by hundreds of miles. An alternative approach, that bares more similarity to natural photosynthesis, employs mobile NADH/NAD + -like species that shuttle between the light absorber and a proximate, yet unilluminated, location where catalysis occurs. Additionally, such a remote approach to solar photocatalysis was recently proposed for the reduction of carbon oxides, CO 2 and CO, to methanol by cascade catalysis. This developing artificial photosynthetic approach offers the promise of catalytic generation of methanol and oxygen gas with sunlight as the sole energy source and CO 2 and water as the only chemical feedstocks. This Viewpoint evaluates the strengths and weaknesses of this approach with an emphasis on CO reduction catalysis with photorecyclable hydride donors while looking forward to what might reasonably be achieved with continued research.

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

Ozonolysis of selenium: an alternative oxidation method for radiochemical separations of arsenic and selenium

Many arsenic and selenium radiochemical separation methods use hydrogen peroxide (H 2 O 2 ) to oxidize selenite (Se(IV)) to selenate (Se(VI)), but this reaction is challenging to control and replicate. Here, this study introduces a simple ozonolysis apparatus with an in-line oxygen-ozone generator and impinger system for rapid selenium oxidation in aqueous samples as an alternative to H 2 O 2 . The system quickly converts Se(IV) to Se(VI), enabling successful separations of arsenic-73 and selenium-75 with high recoveries using ion-exchange chromatography (1-X8). Compared to traditional H 2 O2 treatment, ozone oxidation is a faster and more easily controlled method for selenium redox chemistry.

and nuclear chemistry↗
DOE OSTI2022

Emerging Electrochemical Techniques for Probing Site Behavior in Single-Atom Electrocatalysts

Single-atom catalysts (SACs) have aroused tremendous interest over the past decade, particularly in the community of energy and environment-related electrocatalysis. A rapidly growing number of recent publications have recognized it as a promising candidate with maximum atomic utilization, distinct activity, and selectivity in comparison to bulk catalysts and nanocatalysts. However, the complexity of localized coordination environments and the dispersion of isolated sites lead to significant difficulties when it comes to gaining insight into the intrinsic behavior of electrocatalytic reactions. Furthermore, the low metal loadings of most SACs make conventional ensemble measurements less likely to be accurate on the subnanoscale. Thus, it remains challenging to probe the activity and properties of individual atomic sites by available commercial instruments and analytical methods. In spite of this, continuing efforts have lately focused on the development of advanced measurement methodologies, which are very useful to the fundamental understanding of SACs. There have recently been a number of in situ/operando techniques applied to SACs, such as electron microscopy, spectroscopy, and other analysis methods, which support relevant functions to identify the active sites and reaction intermediates and to investigate the dynamic behavior of localized structures of the catalytic sites. This Account aims to present recent electrochemical probing techniques which can be used to identify single-atomic catalytic sites within solid supports. First, we describe the basic principles of molecular probe methods for the study and analysis of electrocatalytic site behavior. In particular, the in situ probing technique enabled by surface interrogation scanning electrochemical microscopy (SISECM) can measure the active site density and kinetic rate with high resolution. An alternative electrochemical probing technique is further demonstrated on the basis of single-entity electrochemistry, which allows the unique electrochemical imaging of the size and catalytic rate of single atoms, molecules, and clusters. Next, the merits and limitations of different electrochemical techniques are then discussed, along with perspectives for future prospects. Apart from this, we further showcase the powerful capability of emerging electrochemical probing techniques for determining significant effects and properties of SACs for various electrocatalytic reactions, including oxygen reduction and evolution, hydrogen evolution, and nitrate reduction. Overall, electrochemical techniques with atomic resolution have greatly increased opportunities for observing, measuring, and understanding the surface and interface chemistry during energy conversion. In the future, it is anticipated that the development of electrochemical probing techniques will be advanced with innovative perspectives on the behavior and features of SACs. We hope that this Account can contribute in several ways to promoting the fundamental knowledge and technical progress of emerging electrochemical measurements for studying SACs.

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

Synchrotron X-ray diffraction of pyrolusite (MnO 2 ) and rutile (TiO 2 ) during heating to ~1000 °C

To compare thermal expansion behaviors in isomorphic structures with different redox behaviors, we separately heated pyrolusite (Mn 4+ O 2 ) and rutile (Ti 4+ O 2 ) powders from 25 to ~1000 °C at a rate of 0.05 °C/s at ambient pressure and analyzed them using synchrotron X-ray diffraction and Rietveld refinement. The pyrolusite exhibited two reduction-induced phase decompositions. Between 531 and 583 °C, pyrolusite decomposed to bixbyite (Mn 3+ 2 O 3 ), and between 972 and 998 °C, bixbyite decomposed to hausmannite (Mn 2+ Mn 3+ 2 O 4 ). The rutile experienced no phase decompositions or transitions over this same temperature interval. The refined bond lengths and angles for pyrolusite showed that the Mn 4+ coordination octahedron became more distorted near the phase decomposition to bixbyite due to the approach of two coordinating oxygen atoms. The 3d electrons of each Mn 4+ ion in pyrolusite make π bonds with the 2p electrons of the surrounding O 2- ions, whereas the Ti 4+ of rutile has no 3d electrons. Thus, π bonding between octahedral Mn 4+ and the surrounding O 2- anions increases the strength of the Mn–O bonds of pyrolusite relative to the Ti–O bonds of rutile. However, we observed a small decrease in O–O distances in pyrolusite before the decomposition, suggesting that at high temperature, increased π bonding between adjacent O anions precedes the release of O 2 and the reduction of Mn 4+ to Mn 3+ . Analogous behavior was observed for bixbyite before its reductive phase decomposition to hausmannite. In contrast, no anomalous changes in the O–O distances occurred for rutile. Our X-ray diffraction analyses provided accurate thermal expansion coefficients for these materials over a broader temperature range than reported in previous studies. The Mn–O bond lengths in pyrolusite were shorter and stronger than the Ti–O bonds of rutile; for example, at 60 °C, bond distances in pyrolusite refined to 1.8854(6) Å whereas the bond lengths of rutile were 1.9575(4) Å. Accordingly, the axial and volumetric thermal expansion coefficients refined for rutile were greater than those for pyrolusite. Further, the axial coefficients of thermal expansion (CTE) for pyrolusite were 96% (a-axis) and 69% (c-axis) of the corresponding values for rutile, and the volumetric CTE for pyrolusite was 85% of that for rutile.

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

Elucidating the geometric and electronic structure of a fully sulfided analog of an Anderson polyoxomolybdate cluster

The catalytic activity of transition metal sulfide (TMS) clusters in small molecule activation, redox transformations, and charge transfer has inspired the design of novel TMS-based materials for energy-related catalysis and chemical applications. Polyoxometalates (POMs), known for their structural diversity, can in principle be transformed into TMS clusters; however, fully sulfided analogs are rarely isolated, likely due to the strong tendency of uncapped TMS clusters to agglomerate. Here, we report the geometric and electronic structure of a capping ligand-free fully sulfided analog of heptamolybdate Anderson POM [Mo VI 7 O 24 ] 6− , synthesized through the sulfidation of a nanoconfined POM secured within a porous Zr-metal organic framework (NU-1000). A combined computational and experimental analysis indicates that the sulfided counterpart of the Anderson POM is geometrically and electronically more sophisticated than the parent POM. Comparison of experimental pair distribution function (PDF) data with computational simulations confirms that, unlike the oxygen-only [Mo VI 7 O 24 ] 6− cluster, the [Mo IV 7 (μ 3 -S) 6 (μ 2 -SH) 6 (S 2 ) 6 ] 2− polythiometalate (PTM) exhibits diverse sulfur anions (S 2− , HS − , S 2 2− ). DFT calculations indicate that H 2 S acts as a reducing agent, and together with terminal disulfide (S 2 2− ) ligands in the PTM structure, facilitates the complete reduction of all seven Mo VI centers in the parent POM to Mo IV . These findings are supported by X-ray photoelectron spectroscopy (XPS), which confirms exclusive Mo IV , and elemental analysis, which shows quantitative sulfur incorporation. Difference envelope density (DED) mapping further reveals that the PTM clusters are spatially confined within the MOF pores, preventing agglomeration and preserving molecular integrity.

Rabbani, S. M. Gulam [The Ohio State University, C↗
DOE OSTI2023

Long-Term Stability of Ferri-/Ferrocyanide as an Electroactive Component for Redox Flow Battery Applications: On the Origin of Apparent Capacity Fade

We assess the suitability of potassium ferri-/ferrocyanide as an electroactive species for long-term utilization in aqueous organic redox flow batteries. A series of electrochemical and chemical characterization experiments was performed to distinguish between structural decomposition and apparent capacity fade of ferri-/ferrocyanide solutions used in the capacity-limiting side of a flow battery. Our results indicate that, in contrast with previous reports, no structural decomposition of ferri-/ferrocyanide occurs at tested pH values as high as 14 in the dark or in diffuse indoor light. Instead, an apparent capacity fade takes place due to a chemical reduction of ferricyanide to ferrocyanide, via chemical oxygen evolution reaction. We find that this parasitic process can be further exacerbated by carbon electrodes, with apparent capacity fade rates at pH 14 increasing with an increased ratio of carbon electrode surface area to ferricyanide in solution. Based on these results, we report a set of operating conditions that enables the long-duration cycling of alkaline ferri-/ferrocyanide electrolytes and demonstrate how apparent capacity fade rates can be engineered by the initial system setup. If protected from direct exposure to light, the structural stability of ferri-/ferrocyanide anions allows for their practical deployment as electroactive species in long duration energy storage applications.

25 ENERGY STORAGE↗
DOE OSTI2022

Fluorination‐Enhanced Surface Stability of Disordered Rocksalt Cathodes

Abstract Cation‐disordered rocksalt (DRX) oxides are a promising new class of high‐energy‐density cathode materials for next‐generation Li‐ion batteries. However, their capacity fade presents a major challenge. Partial fluorine (F) substitution into the oxygen (O) lattice appears to be an effective strategy for improving the cycling stability, but the underlying atomistic mechanism remains elusive. Here, using a combination of advanced transmission electron microscopy based imaging and spectroscopy techniques, the structural and chemical evolution upon cycling of Mn‐based DRX cathodes with an increasing F content (Li–Mn–Nb–O–F x , x = 0, 0.05, 0.2) are probed. The atomic origin behind the beneficial effect of high‐level fluorination for enhancing the surface stability of the DRX is revealed. It is discovered that, due to the reduced O redox activity while with increasing F concentration, F in the DRX lattice mitigates the formation of an O‐deficient surface layer upon cycling. For low F‐substituted DRX, the O loss near the surface results in the formation of an amorphous cathode–electrolyte interphase layer and nanoscale voids after extended cycling. Increased F concentration in the DRX lattice minimizes both O loss and the interfacial reactions between DRX and the liquid electrolyte, enhancing the surface stability of DRX. These results provide guidance on the development of next‐generation cathode materials through anion substitution.

Li, Linze↗
DOE OSTI2021

Understanding the Role of Lithium Iodide in Lithium–Oxygen Batteries

Lithium–oxygen (Li–O 2 ) batteries possess a high theoretical energy density, which means they could become a potential alternative to lithium-ion batteries. Nevertheless, the charging process of Li–O 2 batteries requires much higher energy, due to the insulating nature of the discharge product. It has been revealed that the anion additive, lithium iodide (LiI), can tune the cell chemistry to form lithium hydroxide (LiOH) as the product and facilitate the kinetics during the charging process. Although numerous studies have been reported, the role of this additive is still under investigation. Herein, the recent advances focusing on the use of LiI in Li–O 2 batteries are reviewed, its catalytic behavior on discharge and charge is discussed, and its synergistic effect with water is understood. Here, the ambiguity existing among the studies are also revealed, and solutions to the current issues are introduced.

25 ENERGY STORAGE↗
DOE OSTI2025

Atomically Revealing Bulk Point Defect Dynamics in Hydrogen‐Driven γ‐Fe 2 O 3 → Fe 3 O 4 → FeO Transformation

Understanding how point defects in the bulk govern redox transformations is essential for advancing hydrogen-based metal production and designing high-performance oxide materials. This study reveals the atomic-scale mechanisms driving hydrogen-induced reduction of γ-Fe 2 O 3 to Fe 3 O 4 , focusing on how bulk vacancy dynamics dictate structural evolution and reaction kinetics. A key finding is the pronounced contrast in defect behavior between the two oxides: in γ-Fe 2 O 3 , intrinsic Fe vacancies promote oxygen vacancy clustering, destabilizing the local lattice and driving nanopore formation. In contrast, Fe 3 O 4 exhibits a higher oxygen vacancy formation energy and lacks intrinsic Fe vacancies, suppressing vacancy aggregation and maintaining a dense, pore-free structure. This divergence governs distinct reduction pathways—γ-Fe 2 O 3 undergoes an interface-reaction-limited transformation confined to the γ-Fe 2 O 3 /Fe 3 O 4 boundary, while Fe 3 O 4 supports a uniform increase in oxygen vacancy concentration, enabling bulk-phase reduction to lower-oxide FeO. Integrated in situ electron microscopy and density functional theory modeling uncover a vacancy-mediated mechanism, where synergistic cation-anion vacancy dynamics steer microstructure evolution and phase progression. These insights highlight the critical role of vacancy dynamics in controlling oxide reactivity and offer a pathway toward vacancy engineering to enhance reduction kinetics in hydrogen metallurgy and to tailor porosity, reactivity, and structural resilience in oxide-based catalysts and energy materials.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Untapped Potential of Fluoride Ions in Maximizing the Electrochemical Stability of Deep Eutectic Solvents

Advancing the batteries is pivotal to propelling our society toward a sustainable, electrified future. The stability of electrolytes forms the backbone of energy storage systems. This is particularly the case for redox flow batteries (RFBs). Their deployability depends on their longevity and dependability. The presence of unstable electrolytes can trigger undesirable reactions, degrade performance, and lead to battery failure. Aqueous electrolytes, with limited electrochemical stability window (ESW), are prone to hydrogen and oxygen evolution. Conversely, non-aqueous electrolytes offer enhanced stability. In this study, we unveil the ESW of a non-aqueous eutectic solvent, comprising choline fluoride and ethylene glycol—a composition that has eluded experimental investigation until now. Our findings show that the stability window, reduction and oxidation potential limits of deep eutectic solvents, are sensitive to variations in the halide component of the ammonium salt. Furthermore, this work not only highlights the benefits of novel deep eutectic solvents but also sets the stage for their strategic use in future battery electrolytes.

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

Quantitative Decoupling of Oxygen-Redox and Manganese-Redox Voltage Hysteresis in a Cation-Disordered Rock Salt Cathode

Pronounced voltage hysteresis in Li-excess cathode materials is commonly thought to be associated with oxygen redox. However, these materials often possess overlapping oxygen and transition-metal redox, whose contributions to hysteresis between charge and discharge are challenging to distinguish. In this work, a two-step aqueous redox titration is developed with the aid of mass spectrometry (MS) to quantify oxidized lattice oxygen and Mn 3+/4+ redox in a representative Li-excess cation-disordered rock salt—Li 1.2 Mn 0.4 Ti 0.4 O 2 (LMTO). Two MS-countable gas molecules evolve from two separate titrant-analyte reactions, thereby allowing Mn and O redox capacities to be decoupled. The decoupled O and Mn redox coulombic efficiencies are close to 100% for the LMTO cathode, indicating high charge-compensation reversibility. As incremental Mn and O redox capacities are quantitatively decoupled, each redox voltage hysteresis is further evaluated. Overall, LMTO voltage hysteresis arises not only from an intrinsic charge-discharge voltage mismatch related to O redox, but also from asymmetric Mn-redox overvoltages. The results reveal that O and Mn redox both contribute substantially to voltage hysteresis. In conclusion, this work further shows the potential of designing new analytical workflows to experimentally quantify key properties, even in a disordered material having complex local coordination environments.

25 ENERGY STORAGE↗
DOE OSTI2023

Synthetic Access to a Framework-Stabilized and Fully Sulfided Analogue of an Anderson Polyoxometalate that is Catalytically Competent for Reduction Reactions

Polyoxometalates (POMs) featuring 7, 12, 18, or more redox-accessible transition metal ions are ubiquitous as selective catalysts, especially for oxidation reactions. The corresponding synthetic and catalytic chemistry of stable, discrete, capping-ligand-free polythiometalates (PTMs), which could be especially attractive for reduction reactions, is much less well developed. Among the challenges are the propensity of PTMs to agglomerate and the tendency for agglomeration to block reactant access of catalyst active sites. Nevertheless, the pervasive presence of transition metal sulfur clusters metalloenzymes or cofactors that catalyze reduction reactions and the justifiable proliferation of studies of two-dimensional (2D) metal-chalcogenides as reduction catalysts point to the promise of well-defined and controllable PTMs as reduction catalysts. Here, we report the fabrication of agglomeration-immune, reactant-accessible, capping-ligand-free Co II Mo 6 IV S 24 n– clusters as periodic arrays in a water-stable, hierarchically porous Zr-metal–organic framework (MOF; NU1K) by first installing a disk-like Anderson polyoxometalate, Co III Mo 6 VI O 24 m– , in size-matched micropores where the siting is established via difference electron density (DED) X-ray diffraction (XRD) experiments. Flowing H 2 S, while heating, reduces molybdenum(VI) ions to Mo(IV) and quantitatively replaces oxygen anions with sulfur anions (S 2– , HS – , S 2 2– ). DED maps show that MOF-templated POM-to-PTM conversion leaves clusters individually isolated in open-channel-connected micropores. Importantly, the structure of the immobilized cluster as determined, in part, by X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS) analysis, and pair distribution function (PDF) analysis of total X-ray scattering agrees well with the theoretically simulated structure. PTM@MOF displays both electrocatalytic and photocatalytic competency for hydrogen evolution. Nevertheless, the initially installed PTM appears to be a precatalyst, gaining competency only after the loss of ~3 to 6 sulfurs and exposure to hydride-forming metal ions.

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

Mechanism of Chlorine-Mediated Electrochemical Ethylene Oxidation in Saline Water

Chlorine as a redox mediator allows for the selective oxidation of ethylene to 2-chloroethanol, which converts to ethylene oxide in alkaline aqueous electrolyte. This strategy utilizes abundant saline water as an electrolyte and source of oxygen atoms for functionalization. We present a mechanistic study of ethylene oxidation in saline water using cobalt oxide nanoparticle catalysts. Electrochemical kinetic analysis and in situ X-ray absorption spectroscopy suggest that the resting state of the catalyst and the rate-determining step differ for the chlorine evolution reaction in the presence and absence of ethylene. In 0.6 M NaCl pH 8 electrolyte, which resembles seawater, the average current density was ~60 mA/cm 2 with a Faradaic efficiency of ~41% toward ethylene functionalization. The use of synthetic and natural seawater achieved Faradaic efficiencies above 70%, while the partial current toward the product remained invariant. Further conversion of the initial product 2-chloroethanol into ethylene glycol was also demonstrated. Here, we present a broader vision of harnessing saline water in electrochemical functionalization of organic molecules and coproduction of hydrogen.

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

One Beam, Dual Insights: Simultaneous Chemical and Structural Changes in Nanopatterned Ceria under Reaction Conditions

Ceria’s interaction with hydrogen can proceed through multiple chemical forms (hydride, hydroxyl, and oxyhydroxide-like), with consequences for the oxidation state, density, and morphology that are rarely tracked in the same evolving state. Here, in this work, we show that under mild H 2 (and H 2 and CO 2 ) environments nanopatterned ceria undergoes oxidation-state changes accompanied by hydrogen incorporation that increases the effective electron density, establishing the following order: CeO 2 Hy > CeO 2 > CeO 2–x Hy > CeO 2–x . In parallel, the surface roughens in a chemically specific manner, with the largest changes coinciding with conditions where incorporated hydrogen is driven to react with oxygen supplied either by air exposure between experiments or by added CO 2 . We obtained these insights by using a single X-ray beam to simultaneously perform ambient-pressure X-ray photoelectron spectroscopy and grazing-incidence X-ray scattering on the same sample spot. Single-mode measurements can miss key ceria–H 2 transformations relevant to optimizing ceria-based hydrogenation catalysts and supports.

anions↗
DOE OSTI2026

Translating Fundamental Insights into Ag-Based Bimetallic Electrocatalysts to Anion-Exchange Membrane Fuel Cells

To address challenges of high costs and scalability for fuel cells, it is essential to develop af-fordable and earth-abundant materials that are Pt-group-metal (PGM)-free. Recent advance-ments in PGM-free electrocatalysis for the oxygen reduction reaction (ORR) in alkaline media show that high catalyst loadings are needed to achieve high reaction rates; however, there are associated mass transport limitations. To address this issue, we develop low-loading ionomer-less Ag-bimetallic thin films by alloying with 3d block elements or Sn. We bridge knowledge from fundamental rotating disk electrode (RDE) studies to gas-diffusion cathodes in high-temperature anion-exchange membrane fuel cells (HT-AEMFCs), resulting in high-activity ORR catalysis and peak power densities up to 1.2 W cm-² geo for the Ag-Sn and Ag-Co alloys. Here, experimental post-characterization and theoretical calculations reveal small Co or Sn oxide nano-islands on Ag as likely active sites enhancing ORR activity, ultimately offering these low-loading PGM-free ORR materials as a viable path towards sustainable energy conversion.

Catalysts↗