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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Virtual Issue: Designing Polymers for Use in Electrochemical Energy Storage Devices

In this Virtual Issue, we focus on the chemistry of macromolecules needed to advance electrochemical energy storage devices—including pseudo-capacitors as well as lithium-ion, lithium-metal, magnesium-metal, and redox-flow batteries—for widespread electrification of transportation and storage on the grid. Success on these fronts hinges on the development of batteries with strict design specifications that carry concomitant demands for the battery’s architecture, embodied chemistry, and individual components (i.e., electrolytes, membranes, electrodes, etc.), which are inextricably coupled in their functions. Finally, all must work together to provide long-lasting solutions that can be commercialized and deployed widely at a cost that disrupts the market, which is currently dominated by the coal, oil, and gas industries.

25 ENERGY STORAGE↗
DOE OSTI2022

Selectivity of Electrochemical Ion Insertion into Manganese Dioxide Polymorphs

The ion insertion redox chemistry of manganese dioxide has diverse applications in energy storage, catalysis, and chemical separations. Unique properties derive from the assembly of Mn–O octahedra into polymorphic structures that can host protons and nonprotonic cations in interstitial sites. Despite many reports on individual ion-polymorph couples, much less is known about the selectivity of electrochemical ion insertion in MnO 2 . In this work, we use density functional theory to holistically compare the electrochemistry of A x MnO 2 (where A = H + , Li + , Na + , K + , Mg 2+ , Ca 2+ , Zn 2+ , Al 3+ ) in aqueous and nonaqueous electrolytes. We develop an efficient computational scheme demonstrating that Hubbard-U correction has a greater impact on calculating accurate redox energetics than choice of exchange-correlation functional. Using PBE+U, we find that for nonprotonic cations, ion selectivity depends on the oxygen coordination environments inside a polymorph. When H + is present, however, the driving force to form hydroxyl bonds is usually stronger. In aqueous electrolytes, only three ion-polymorph pairs are thermodynamically stable within water’s voltage stability window (Na + and K + in α-MnO 2 , and Li + in λ-MnO 2 ), with all other ion insertion being metastable. We find Al 3+ may insert into the δ, R, and λ polymorphs across the full 2-electron redox of MnO 2 at high voltage; however, electrolytes for multivalent ions must be designed to impede the formation of insoluble precipitates and facilitate cation desolvation. We also show that small ions coinsert with water in α-MnO 2 to achieve greater coordination by oxygen, while solvation energies and kinetic effects dictate water coinsertion in δ-MnO 2 . Finally, taken together, these findings explain reports of mixed ion insertion mechanisms in aqueous electrolytes and highlight promising design strategies for safe, high energy density electrochemical energy storage, desalination batteries, and electrocatalysts.

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

Understanding Cation Selectivity in Carbon Nanopores with Hybrid First-Principles/Continuum Simulations: Implications for Water Desalination and Separation Technologies

Understanding ion adsorption in porous carbons is crucial for a range of technologies, including water desalination and energy storage. In this work, we combined density functional theory with a continuum solvation model to investigate thermodynamics and kinetics of the adsorption process of alkali metal ions from aqueous solutions into carbon nanopores with different sizes and geometries. We found that cations with a larger ionic radius are more favorable to enter the nanopores because of a lower energy penalty of dehydration. In addition, the pore size and geometry were found to have a significant impact on the ion–pore interaction under confinement and cation selectivity. Our study highlights a complex interplay among nanopore geometry, ion size, and hydration on the cation adsorption selectivity, suggesting that tuning the porosity could represent a general strategy for improving ion separations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Interplay between Swelling Kinetics and Nanostructure in Perfluorosulfonic Acid Thin-Films: Role of Hygrothermal Aging

Impacts of processing, storage, and operation on thin-film perfluorosulfonic acid (PFSA) ionomer coatings used in electrodes of electrochemical devices remains unestablished. In this work, alteration of structure–function relationship in ionomers is achieved via exposure to elevated temperature and humidity (hygrothermal aging). Findings reflect a strong inverse correlation between aging-induced ionomer thin-film domain orientation and water-transport kinetics evaluated from swelling. Finally, impact of aging is shown to be more pronounced on platinum due to interactions with PFSA, as evidenced by greater increase in nanodomain orientation parallel to substrate accompanied by reduced water transport, in contrast to silicon support.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Monocopper active site for partial methane oxidation in Cu-exchanged 8MR zeolites

Direct conversion of methane to methanol using oxygen is experiencing renewed interest owing to the availability of new natural gas resources. Copper-exchanged zeolites such as mordenite and ZSM-5 have shown encouraging results, and di- and tri-copper species have been suggested as active sites. Recently, small eight-membered ring (8MR) zeolites including SSZ-13, -16, and -39 have been shown to be active for methane oxidation, but the active sites and reaction mechanisms in these 8MR zeolites are not known. In this work, we use density functional theory (DFT) calculations to systematically evaluate monocopper species as active sites for the partial methane oxidation reaction in Cu-exchanged SSZ-13. On the basis of kinetic and thermodynamic arguments, we suggest that [Cu II OH] + species in the 8MR are responsible for the experimentally observed activity. Furthermore, our results successfully explain the available spectroscopic data and experimental observations including (i) the necessity of water for methanol extraction and (ii) the effect of Si/Al ratio on the catalyst activity. Monocopper species have not yet been suggested as an active site for the partial methane oxidation reaction, and our results suggest that [Cu II OH] + active site may provide complementary routes for methane activation in zeolites in addition to the known [Cu–O–Cu] 2+ and Cu 3 O 3 motifs.

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

Simulations and Experiments Reveal Effect of Nanopores on Helium Diffusion in Quartz

The diffusion properties of noble gases in minerals are widely used to reconstruct the thermal histories of rocks. In this work, we combine density functional theory (DFT) calculations with laboratory experiments to investigate controls on helium diffusion in quartz. DFT calculations for perfect α-quartz predict substantially lower activation energies and frequency factors for helium diffusion than observed in laboratory experiments, especially in the [001] direction. These results imply that no helium could be retained in quartz at Earth surface temperatures, which conflicts with observations of partial cosmogenic 3 He retention over geologic time scales. Here, we implement a model of helium diffusion in α-quartz modulated by nanopore defects that disrupt energetically favorable diffusion pathways. In this model, we find that laboratory-determined diffusivities can be most closely reproduced when a helium atom encounters ~70 nanopore sites per million interstitial sites. The results of our model indicate that diffusion of helium in natural quartz, like other noble gases in other minerals, can be significantly modulated by extended defects.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Enhancing Catalytic Activity of MoS2 Basal Plane S-Vacancy by Co Cluster Addition

The basal plane of molybdenum disulfide (MoS 2 ) was recently activated for hydrogen evolution reaction (HER) by creating sulfur (S) vacancies (MoS 2-x ). However, the HER activity of those S-vacancies depends on the concentration of S-vacancies, imposing a dilemma for either improving activity per site or increasing overall active site density. In this work, we use density functional theory (DFT) calculations and experiments to show that the HER activities of MoS2-x are greatly enhanced by adding cobalt (Co) clusters on the basal plane. Furthermore, our DFT results show that the highest HER activity is achieved when the Co clusters are anchored on the S-vacancies with the interface of Co-Mo as the preferred active site. Our experiments confirm that the addition of Co enhances the activity per unit active site and increases the electrochemical active surface area. These results demonstrate the basal plane activity of MoS 2-x can be enhanced by decorating S-vacancies with transition-metal clusters.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

DFT Investigation of Ammonia Formation via a Langmuir–Hinshelwood Mechanism on Mo-Terminated δ-MoN(0001)

In this work, we employed density functional theory to elucidate the energetics associated with elementary steps along a Langmuir-Hinshelwood mechanism for the Haber-Bosch synthesis of ammonia from N 2 and H 2 on a hexagonal, Mo-terminated molybdenum nitride surface. Using nudged elastic band calculations, we determined the energy barriers involved in the reaction processes. An active site consisting of four nearest-neighbor Mo atoms, previously identified as an active site on similar surfaces, was chosen to investigate the reaction processes. Using this approach, we calculate a barrier of ~0.5 eV for the dissociation of N 2 . The superior activity of the dissociation of the strong N 2 bonds is rationalized based on the unique geometric and electronic configurations present at these active sites. Despite the favorable energetics for nitrogen dissociation, the energy cost for hydrogenation of NH x (0 ≤ x ≤ 2) species is shown to be energetically limiting for the formation of ammonia through the Langmuir-Hinshelwood mechanism at these sites, with elementary step activation barriers calculated to be as large as ~2 eV. A comparison to Haber-Bosch results derived from a similar γ-Mo 2 N model system suggests the relative independence of surface chemistry and bulk stoichiometry for rhombic Mo 4 active sites present on molybdenum nitrides.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Theoretical Investigations into Defected Graphene for Electrochemical Reduction of CO 2

Here, despite numerous experimental efforts that have been dedicated to studying carbon-based materials for electrochemical reduction of CO 2 , a rationalization of the associated trends in the intrinsic activity of different active motifs has so far been elusive. In the present work, we employ density functional theory calculations to examine a variety of different active sites in N-doped graphene to give a comprehensive outline of the trends in activity. We find that adsorption energies of COOH* and CO* do not follow the linear scaling relationships observed for the pure transition metals, and this unique scaling is rationalized through differences in electronic structure between transition metals and defected graphene. This finding rationalizes most of the experimental observations on the carbon-based materials which present promising catalysts for the two-electron reduction of CO 2 to CO. With this simple thermodynamic analysis, we identify several active sites that are expected to exhibit a comparable or even better activity to the state-of-the-art gold catalyst, and several configurations are suggested to be selective for CO 2 RR over HER.

36 MATERIALS SCIENCE↗
DOE OSTI2021

A Theory-Guided X-ray Absorption Spectroscopy Approach for Identifying Active Sites in Atomically Dispersed Transition-Metal Catalysts

Atomically dispersed supported metal catalysts offer new properties and the benefits of maximized metal accessibility and utilization. The characterization of these materials, however, remains challenging. Using atomically dispersed platinum supported on crystalline MgO (chosen for its well-defined bonding sites) as a prototypical example, we demonstrate in this work how systematic density functional theory calculations for assessing all the potentially stable platinum sites, combined with automated analysis of extended X-ray absorption fine structure (EXAFS) spectra, leads to unbiased identification of isolated, surface-enveloped platinum cations as the catalytic species for CO oxidation. The catalyst has been characterized by atomic-resolution imaging and EXAFS and high-energy resolution fluorescence detection X-ray absorption near edge spectroscopy. The proposed platinum sites are in agreement with experiment. This theory-guided workflow leads to rigorously determined structural models and provides a more detailed picture of the structure of the catalytically active site than what is currently possible with conventional EXAFS analyses. As this approach is efficient and agnostic to the metal, support, and catalytic reaction, we posit that it will be of broad interest to the materials characterization and catalysis communities.

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

Theoretical Prediction and Experimental Verification of IrO x Supported on Titanium Nitride for Acidic Oxygen Evolution Reaction

Reducing iridium (Ir) catalyst loading for acidic oxygen evolution reaction (OER) is a critical strategy for large-scale hydrogen production via proton exchange membrane (PEM) water electrolysis. However, simultaneously achieving high activity, long-term stability, and reduced material cost remains challenging. To address this challenge, we develop a frame-work by combining density functional theory (DFT) prediction using model surfaces and proof-of-concept experimental ver-ification using thin films and nanoparticles. DFT results predict that oxidized Ir monolayers over titanium nitride (IrO x /TiN) should display higher OER activity than IrO x while reducing Ir loading. Further, this prediction is verified by depositing Ir monolayers over TiN thin films via physical vapor deposition. The promising thin film results are then extended to commercially viable powder IrO x /TiN catalysts, which demonstrate a lower overpotential and higher mass activity than commercial IrO 2 , and a long-term stability of 250 hours to maintain a current density of 10 mA cm -2 . The superior OER performance of IrO x /TiN is further confirmed using proton exchange membrane water electrolyzer (PEMWE), which shows a lower cell voltage than commercial IrO 2 to achieve a current density of 1 A cm -2 . Both DFT and in situ X-ray absorption spectroscopy reveal that the high OER performance of IrO x /TiN strongly depends on the IrO x - TiN interaction via direct Ir-Ti bonding. This study highlights the importance of close interaction between theoretical prediction based on mechanistic understanding and experimental verification based on thin film model catalysts to facilitate the development of more practical powder IrO x /TiN catalysts with high activity and stability for acidic OER.

08 HYDROGEN↗
DOE OSTI2026

Node Distortions as a Means of Defect Engineering in Zr-Based MOFs

Defect engineering in Zr-based metal–organic frameworks (Zr-MOFs) has focused primarily on missing-linker defects. However, recent studies suggest that node dehydroxylation–which creates distortions and coordinatively unsaturated Zr sites (Zr cus )–may have a more significant impact on properties. The present work uses pair distribution function (PDF) and thermogravimetric analysis coupled with systematic defect manipulation to study the effect of node dehydroxylation and missing-linker defects in UiO-66. By employing rapid heat treatment (RHT) under humid flow, we tracked the transition from high-symmetry [Zr 6 O 4 (OH) 4 ] 12+ to distorted [Zr 6 O 6 ] 12+ nodes. This structural evolution significantly improves As(V) uptake, whereas increasing the number of missing linkers–via chemical treatment or RHT of mixed-ligand frameworks–fails to enhance performance. Crucially, our detection of distorted nodes in as-synthesized UiO-66 also raises the possibility that these defects were silently present in many earlier studies that span various applications, where their role in governing performance may have been inadvertently overlooked. The present study challenges the prevailing “missing-linker” paradigm and establishes cluster dehydroxylation as a defect-engineering strategy to enhance Lewis-acidic performance in Zr-MOFs.

Adsorption↗
DOE OSTI2020

Tunable analog thermal material

Naturally-occurring thermal materials usually possess specific thermal conductivity ($\textit{κ}$), forming a digital set of $\textit{κ}$ values. Emerging thermal metamaterials have been deployed to realize effective thermal conductivities unattainable in natural materials. However, the effective thermal conductivities of such mixing-based thermal metamaterials are still in digital fashion, i.e., the effective conductivity remains discrete and static. Here, we report an analog thermal material whose effective conductivity can be in-situ tuned from near-zero to near-infinity $\textit{κ}$. The proof-of-concept scheme consists of a spinning core made of uncured polydimethylsiloxane (PDMS) and fixed bilayer rings made of silicone grease and steel. Thanks to the spinning PDMS and its induced convective effects, we can mold the heat flow robustly with continuously changing and anisotropic $\textit{κ}$. Our work enables a single functional thermal material to meet the challenging demands of flexible thermal manipulation. It also provides platforms to investigate heat transfer in systems with moving components.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Chemomechanical modification of quantum emission in monolayer WSe2

Abstract Two-dimensional (2D) materials have attracted attention for quantum information science due to their ability to host single-photon emitters (SPEs). Although the properties of atomically thin materials are highly sensitive to surface modification, chemical functionalization remains unexplored in the design and control of 2D material SPEs. Here, we report a chemomechanical approach to modify SPEs in monolayer WSe 2 through the synergistic combination of localized mechanical strain and noncovalent surface functionalization with aryl diazonium chemistry. Following the deposition of an aryl oligomer adlayer, the spectrally complex defect-related emission of strained monolayer WSe 2 is simplified into spectrally isolated SPEs with high single-photon purity. Density functional theory calculations reveal energetic alignment between WSe 2 defect states and adsorbed aryl oligomer energy levels, thus providing insight into the observed chemomechanically modified quantum emission. By revealing conditions under which chemical functionalization tunes SPEs, this work broadens the parameter space for controlling quantum emission in 2D materials.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2017

Analysis and correction of errors in nanoscale particle tracking using the Single-pixel interior filling function (SPIFF) algorithm

Particle tracking, which is an essential tool in many fields of scientific research, uses algorithms that retrieve the centroid of tracked particles with sub-pixel accuracy. However, images in which the particles occupy a small number of pixels on the detector, are in close proximity to other particles or suffer from background noise, show a systematic error in which the particle sub-pixel positions are biased towards the center of the pixel. This “pixel locking” effect greatly reduces particle tracking accuracy. In this report, we demonstrate the severity of these errors by tracking experimental (and simulated) imaging data of optically trapped silver nanoparticles and single fluorescent proteins. We show that errors in interparticle separation, angle and mean square displacement are significantly reduced by applying the corrective Single-Pixel Interior Filling Function (SPIFF) algorithm. Our work demonstrates the potential ubiquity of such errors and the general applicability of SPIFF correction to many experimental fields.

Science & Technology - Other Topics↗
DOE OSTI2024

X-ray Thomson scattering absolute intensity from the f-sum rule in the imaginary-time domain

We present a formally exact and simulation-free approach for the normalization of X-ray Thomson scattering (XRTS) spectra based on the f-sum rule of the imaginary-time correlation function (ITCF). Our method works for any degree of collectivity, over a broad range of temperatures, and is applicable even in nonequilibrium situations. In addition to giving us model-free access to electronic correlations, this new approach opens up the intriguing possibility to extract a plethora of physical properties from the ITCF based on XRTS experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

First-Principles insights into group-V impurities and their impact on germanium detector performance

The outstanding properties of high-purity germanium (HPGe) detectors, such as excellent energy resolution, high energy sensitivity, and a low background-to-signal ratio, make them essential and ideal candidates for detecting particle signatures in nuclear processes such as neutrino-less double beta decay (0νββ). However, the presence of defects and impurities in HPGe crystals can lead to charge trapping, which affects carrier mobility and results in significant energy resolution degradation. In this work, we employ density functional theory with a hybrid functional to study the energetics of possible point defects in Ge. Our findings indicate that group-V impurities form more readily in Ge compared to vacancy and interstitial of Ge. Unlike N dopants, which yield deep trap states, P, As, and Sb create shallow traps close to the conduction band edge of Ge. Furthermore, we predict that group-V defects can condense into defect complexes with Ge vacancies. These vacancy-impurity complexes form deep traps in Ge, similar to Ge vacancies, suggesting that both vacancies and vacancy-impurity complexes contribute to charge trapping in these detectors, thereby diminishing their performance.

36 MATERIALS SCIENCE↗
DOE OSTI2015

The influence of polaron formation on exciton dissociation

A linear tight-binding model was used to examine the yield of exciton dissociation under the influence of the electron–vibration interaction. The system consists of a linear chain, coupled to a single vibration, and electron–vibration interaction is permitted to occur on certain sites. In the presence of this interaction, population tends to localize to build a polaron. The system loses polaron trapping energy to the environment through its coupling to the bath environment, and loses population due to the injection into the electrode at the terminal site. A self-energy term was generated from population injection, and was added to the energy level of the last site, working as a sink function to absorb the electrons and measure the yield. This injection occurs only when the electron energy is inside and around the band. When the electron energy is outside the tight-binding band, population injection is inhibited. Our aim here is to investigate the exciton dissociation effected by the competition between polaron formation and population injection, via a process strongly influenced by the inter-site coupling and the electron–vibration interaction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗