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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Mimicking Natural Photosynthesis: Designing Ultrafast Photosensitized Electron Transfer into Multiheme Cytochrome Protein Nanowires

Efficient nanomaterials for artificial photosynthesis require fast and robust unidirectional electron transfer (ET) from photosensitizers through charge-separation and accumulation units to redox-active catalytic sites. We explored the ultrafast time-scale limits of photo-induced charge transfer between a Ru(II)tris(bipyridine) derivative photosensitizer and PpcA, a 3-heme c-type cytochrome serving as a nanoscale biological wire. Four covalent attachment sites (K28C, K29C, K52C, and G53C) were engineered in PpcA enabling site-specific covalent labeling with expected donor-acceptor (DA) distances of 4–8 Å. X-ray scattering results demonstrated that mutations and chemical labeling did not disrupt the structure of the proteins. Time-resolved spectroscopy revealed three orders of magnitude difference in charge transfer rates for the systems with otherwise similar DA distances and the same number of covalent bonds separating donors and acceptors. All-atom molecular dynamics simulations provided additional insight into the structure-function requirements for ultrafast charge transfer and the requirement of van der Waals contact between aromatic atoms of photosensitizers and hemes in order to observe sub-nanosecond ET. This work demonstrates opportunities to utilize multi-heme c-cytochromes as frameworks for designing ultrafast light-driven ET into charge-accumulating biohybrid model systems, and ultimately for mimicking the photosynthetic paradigm of efficiently coupling ultrafast, light-driven electron transfer chemistry to multi-step catalysis within small, experimentally versatile photosynthetic biohybrid assemblies.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Shedding Light on Primary Donors in Photosynthetic Reaction Centers

Chlorophylls (Chl)s exist in a variety of flavors and are ubiquitous in both the energy and electron transfer processes of photosynthesis. The functions they perform often occur on the ultrafast (fs–ns) time scale and until recently, these have been difficult to measure in real time. Further, the complexity of the binding pockets and the resulting protein-matrix effects that alter the respective electronic properties have rendered theoretical modeling of these states difficult. Recent advances in experimental methodology, computational modeling, and emergence of new reaction center (RC) structures have renewed interest in these processes and allowed researchers to elucidate previously ambiguous functions of Chls and related pheophytins. This is complemented by a wealth of experimental data obtained from decades of prior research. Studying the electronic properties of Chl molecules has advanced our understanding of both the nature of the primary charge separation and subsequent electron transfer processes of RCs. In this review, we examine the structures of primary electron donors in Type I and Type II RCs in relation to the vast body of spectroscopic research that has been performed on them to date. Further, we present density functional theory calculations on each oxidized primary donor to study both their electronic properties and our ability to model experimental spectroscopic data. This allows us to directly compare the electronic properties of hetero- and homodimeric RCs.

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

Mechanisms and Energetics of CO 2 Chemisorption in Choline-Based Eutectic Solvents

Understanding the influences of proton sharing and hydrogen transfer in amine and hydroxyl functionalized eutectic solvents is important for tuning CO 2 binding as they relate to the chemisorption capacity and energetics of solvent regeneration in carbon capture. In this study, we examine how the CO 2 binding mechanism and energetics vary in eutectic solvents composed of choline-based hydrogen-bond acceptors (HBAs) with amine and hydroxyl moieties and ethylene glycol (EG), propylene glycol (PG), 1,2-butanediol (BD), and monoethanolamine (MEA)-type hydrogen-bond donors (HBDs), through absorption–desorption experiments and spectral analysis, supported with density functional theory (DFT) calculations. While the HBD-CO 2 complex is the major and the thermodynamically more favored product of absorption in all of the examined eutectic solvents, this complexation is only possible proceeding a proton transfer from HBD to the HBA in diol-based systems (EG, PG, BD). The interplay between HBA-CO 2 and HBD-CO 2 speciation is governed by the HBD concentration, basicity, and steric effects, with increased HBD-CO 2 interactions in the presence of smaller HBDs (size: BD > PG > EG). On the other hand, in MEA-based systems, CO 2 readily binds to the amine followed by a proton transfer from the amine to the HBA as confirmed by DFT calculations. In this way, the MEA-CO 2 chemisorption capacities exceeded that of the conventional amine (up to 0.93 mol of CO 2 per mol of MEA versus 0.5). Furthermore, the increase in CO 2 capacities and enhanced binding in eutectics including MEA or the more basic HBAs also resulted in regeneration temperatures of 70 to 60 °C with calculated reaction energies of −82 to −57 kJ/mol, compared to 50 °C for others with weaker binding, following CO 2 absorption at 25 °C.

absorption↗
DOE OSTI2026

Edge dislocation mediated anomalous charge transfer in face centered cubic high entropy alloys

The charge transfer in alloys dictates their structural and functional properties. The presence of the line defect can influence the charge transfer characteristics in alloys. The edge dislocation-volume misfit interaction in high entropy alloys is a critical area of interest concerning the development of accurate solid solution strengthening models for these materials. The evolution of the volume misfit of atoms is either studied empirically using Vegard's law or mechanistically using \emph{ab initio} calculations, without considering the effect of edge dislocation on charge transfer explicitly. In this work, we show the influence of edge dislocation on the charge transfer in CoCrFeMnNi, CoCrNi and CoNi using large-scale \emph{ab initio} calculations. The anomalous charge transfer characteristics, in terms of deviations from electronegativity trends, are demonstrated, which are dictated by electronegativity equalisation rather than pair-atom interactions. The deviation of atomic volume in the compressive and tensile stress regions of the edge dislocation is rationalised in terms of anomalous magneto-volume fluctuations in such alloys.

Ghosh, Swarnava [ORNL] (ORCID:0000000338005264)↗
DOE OSTI2025

Trade-offs among restored ecosystem functions are context-dependent in Mediterranean-type regions

Global biodiversity hotspots, including Mediterranean-type ecosystems worldwide, are highly threatened by global change that alters biodiversity, ecosystem functions, and services. Some restoration activities enhance ecosystem functions by reintroducing plant species based on known relationships between plant traits and ecosystem processes. Achieving multiple functions across different site conditions, however, requires understanding how abiotic factors like climate and soil, along with plant assemblages, influence ecosystem functions, including their trade-offs and synergies. We used the ModEST ecosystem simulation model, which integrates carbon, water, and nutrient processes with plant traits, to assess the relationships between restored plant assemblages and ecosystem functions in Mediterranean-type climates and soils. We investigated whether maximised carbon increment, water use efficiency, and nitrogen use efficiency, along with their trade-offs and synergies, varied across different abiotic contexts. Further, we asked whether assemblages that maximised functions varied across environments and among these functions. We found that maximised ecosystem carbon increment and nitrogen use efficiency occurred under moist, warm conditions, while water use efficiency peaked under drier conditions. Generally, the assemblage that maximised one function differed from those for other maximised functions. Synergies were rare, except between water and nitrogen use efficiencies in loam soils across most climates. Trade-offs among maximised functions were common, varying in strength with abiotic context and plant assemblages, and were more pronounced in sandy loam soils compared to clay-rich soils. Our findings suggest that due to variation in abiotic conditions within and across Mediterranean-type regions at the global scale, site-specific plant assemblages are required to maximise ecosystem functions. Thus, lessons from a single site cannot be transferred to another site, even where the same plant functional types are available for restoration. Our simulation results offer valuable insights into potential ecosystem performance under specific abiotic conditions following restoration with particular plant functional types, thereby informing local restoration efforts.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Quantum biology revisited

Photosynthesis is a highly optimized process from which valuable lessons can be learned about the operating principles in nature. Its primary steps involve energy transport operating near theoretical quantum limits in efficiency. Recently, extensive research was motivated by the hypothesis that nature used quantum coherences to direct energy transfer. This body of work, a cornerstone for the field of quantum biology, rests on the interpretation of small-amplitude oscillations in two-dimensional electronic spectra of photosynthetic complexes. This Review discusses recent work reexamining these claims and demonstrates that interexciton coherences are too short lived to have any functional significance in photosynthetic energy transfer. Instead, the observed long-lived coherences originate from impulsively excited vibrations, generally observed in femtosecond spectroscopy. These efforts, collectively, lead to a more detailed understanding of the quantum aspects of dissipation. Nature, rather than trying to avoid dissipation, exploits it via engineering of exciton-bath interaction to create efficient energy flow.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Proton-coupled electron transfer of macrocyclic ring hydrogenation: The chlorinphlorin

Significance The chemical reduction of unsaturated bonds occurs by hydrogenation with H 2 as the reductant. Conversely, in biology, the unavailability of H 2 engenders the typical reduction of unsaturated bonds with electrons and protons from different cofactors, requiring olefin hydrogenation to occur by proton-coupled electron transfer (PCET). Moreover, the redox noninnocence of tetrapyrrole macrocycles furnishes unusual PCET intermediates, including the phlorin, which is an intermediate in tetrapyrrole ring reductions. Whereas the phlorin of a porphyrin is well established, the phlorin of a chlorin is enigmatic. By controlling the PCET reactivity of a chlorin, including the use of a hangman functionality to manage the proton transfer, the formation of a chlorinphlorin by PCET is realized, and the mechanism for its formation is defined.

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

Pick-and-Place Transfer of Arbitrary-Metal Electrodes for van der Waals Device Fabrication

Van der Waals electrode integration is a promising strategy to create nearly perfect interfaces between metals and 2D materials, with advantages such as eliminating Fermi-level pinning and reducing contact resistance. However, the lack of a simple, generalizable pick-and-place transfer technology has greatly hampered the wide use of this technique. Here, we demonstrate the pick-and-place transfer of prefabricated electrodes from reusable polished hydrogenated diamond substrates without the use of any sacrificial layers due to the inherent low-energy and dangling-bond-free nature of the hydrogenated diamond surface. The technique enables transfer of arbitrary-metal electrodes and an electrode array, as demonstrated by successful transfer of eight different elemental metals with work functions ranging from 4.22 to 5.65 eV. We also demonstrate the electrode array transfer for large-scale device fabrication. The mechanical transfer of metal electrodes from diamond to van der Waals materials creates atomically smooth interfaces with no interstitial impurities or disorder, as observed with cross-section high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy. As a demonstration of its device application, we use the diamond transfer technique to create metal contacts to monolayer transition metal dichalcogenide semiconductors with high-work-function Pd, low-work-function Ti, and semimetal Bi to create n- and p-type field-effect transistors with low Schottky barrier heights. We also extend this technology to air-sensitive materials (trilayer 1T’ WTe 2 ) and other applications such as ambipolar transistors, Schottky diodes, and optoelectronics. This highly reliable and reproducible technology paves the way for new device architectures and high-performance devices.

2D materials↗
DOE OSTI2024

Experimental investigation of Multi-Mode heat transfer to a Free-Falling dilute particle cloud in a heated vertical tube

The development of dilute particle heat exchangers and reactors for advanced energy systems requires an understanding of the multi-mode heat transfer from a heated wall to falling particles. This study presents experimental results of the overall heat transfer coefficient for a free-falling, dilute flow of particles with solid volume fraction from 0.0005 to 0.006 corresponding to feed rates from 3.7 kg s -1 m -2 to 44 kg s -1 m -2 in a vertical, heated tube containing quiescent air at atmospheric pressure. Tube wall temperatures are varied between 300°C to 900°C while keeping the particle inlet temperature constant. The experimental results show that the overall heat transfer coefficient is a strong function of particle feed rate and surface temperature. Good agreement was obtained with prior studies conducted at comparable temperatures but lower particle feed rates (< 4 kg m -2 s -1 ). The established correlations for particle-to-wall radiation and particle-to-gas convection were used to estimate the wall-to-gas convective contribution from the measured overall heat transfer coefficient. The experimental results indicated a 4 to 6 times improvement in the wall convection in the solid-gas mixture compared to that expected from natural convection in a single-phase gas. Furthermore, the data presented here are applicable to characterize heat transfer in dilute particle heat exchangers, furnaces, and solar receivers.

14 SOLAR ENERGY↗
DOE OSTI2023

Engineering Functionalized 2D Metal-Organic Frameworks Nanosheets with Fast Li + Conduction for Advanced Solid Li Batteries

Solid-state batteries can ensure high energy density and safety in lithium metal batteries, while polymer electrolytes are plagued by slow ion kinetics and low selective transport of Li + . Metal-organic frameworks (MOFs) are proposed as emerging fillers for solid-state poly(ethylene oxide)(PEO) electrolytes, however, developing functionalized MOFs and understanding their roles on ion transfer has proven challenging. Herein, combining computational and experimental results, the functional group regulation in MOFs can effectively change surficial charge distribution and limit anion movement is revealed, providing a potential solution to these issues. Specifically, functionalized 2D MOF sheets are designed through molecular engineering to construct high-performance composite electrolytes, where the electron-donating effect of substituents in 2D-MOFs effectively limits the movement of ClO 4 - and promotes mechanical properties and ion migration numbers (0.36 up to 0.64) of PEO. As a result, Li/Li cells with composite electrolyte exhibit superior cyclability for 1000 h at a current density of 0.2 mA cm -2 . Meanwhile, the solid LiFePO 4 /Li battery delivers highly reversible capacities of 148.8 mAh g -1 after 200 cycles. In conclusion, these findings highlight a new approach for anion confinement through the use of functional group electronic effects, leading to enhanced ionic conductivity, and a feasible direction for high-performance solid-state batteries.

25 ENERGY STORAGE↗
DOE OSTI2024

Low-Temperature Characterization of a Nonaqueous Liquid Electrolyte for Lithium Batteries

Rechargeable batteries exhibit poor performance at low temperatures due to sluggish ion transport through the electrolytic phase. Ion transport is governed by three transport parameters—conductivity, diffusion coefficient, and the cation transference number with respect to the solvent velocity—and the thermodynamic factor. Understanding how these parameters change with temperature is necessary for designing improved electrolytes. In this work, we combine electrochemical techniques with electrophoretic NMR to determine the temperature dependence of these parameters for a liquid electrolyte, LiTFSI salt dissolved in tetraglyme between −20 and 45 °C. At colder temperatures, all species in the electrolyte tend to move more slowly due to increasing viscosity, which translates to a monotonic decrease in conductivity and diffusion coefficient with decreasing temperature. Surprisingly, we find that the field-induced velocity of solvent molecules at a particular salt concentration is a nonmonotonic function of temperature. The cation transference number with respect to the solvent velocity thus exhibits a complex dependence on temperature and salt concentration. The measured thermodynamic and transport properties are used to predict concentration gradients that will form in a lithium-lithium symmetric cell under a constant applied potential as a function of temperature using concentrated solution theory. The calculated steady current at −20 °C is lower than that at 45 °C by roughly two orders of magnitude.

25 ENERGY STORAGE↗
DOE OSTI2022

A remarkable CHF of 345W/cm 2 is achieved in a wicked-microchannel using HFE-7100

Boiling heat transfer of dielectric fluids is a promising cooling technique for thermal management of microelectronic systems. However, the critical heat flux achievable is generally low, because of the poor thermophysical properties of these fluids. Here, to address this dilemma, we propose a new cooling concept to substantially enhance global liquid supply during phase-change process using enhanced capillary-driven force. Additionally, dedicated vapor pathways are designed among a bank of micro-pillars to facilitate vapor removal. In this work, new wicks comprised of silicon micro-pinfin arrays are explored to significantly enhance the flow boiling heat transfer performance. To examine the functionalities of this wick, experiments on HFE-7100 were carried out with mass velocities varying from 247 to 3,465 kg/m 2 s. To explore the enhancement mechanisms and to analyze the capillary-assisted flow boiling process, visualization studies were conducted. The results indicate that sustainable evaporation induced by wick microstructures and efficient liquid supply are the enhancement mechanisms compared to parallel microchannels with solid walls. It is found that the overall heat transfer coefficient is substantially increased up to 75%. Remarkably, a high critical heat flux (CHF) of approximately 345 W/cm 2 is recorded at G = 3,465 kg/m 2 s at coolant inlet temperature of ~20 °C. Equally importantly, this noticeable enhancement of CHF value is associated with drastically decreased pressure drops compared to microchannels decorated with μ-pinfin fences.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Impact of Side Chain Chemistry on Lithium Transport in Mixed Ion–Electron-Conducting Polymers

We discuss how typical design strategies for mixed ion-electron conduction in polymers have focused on overall ionic conductivity, without specificity for anion vs. cation conduction. Here, we demonstrate that side chain chemistry can be used to control Li+ conductivity in semiconducting polymers. This design principle is significant for applications which require Li+ specific transport, such as Li-ion batteries. We show that a polythiophene functionalized with an ionic liquid side chain demonstrates higher conductivity and lithium transference than a more commonly studied ether-functionalized P3AT derivative. Poly(3-(6’-(N-methylimidazolium) hexyl)thiophene TFSI–) (P3HT-Im+TFSI–) can solvate and conduct ions up to salt concentrations of r=1.0 (where r = [moles of salt]/[moles of monomer]) while achieving ionic conductivity of ≈10–3 S/cm at 80°C, and a lithium transference number of 0.36. On the other hand, poly(3¬-(methoxyethoxyethoxymethyl) thiophene) (P3MEEMT) shows a peak conductivity of ≈10–5 S/cm at r=0.05 and 80°C, with near zero lithium transport. This work shows that multiple high dielectric moieties can be used to drive ion conduction in semiconducting polymers, but diffuse, cationic side chains such as imidazolium are preferred for Li-ion conduction.

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

Impact of functional groups on the electrocatalytic hydrogenation of aromatic carbonyls to alcohols

We report that electrocatalytic hydrogenation (ECH) of biomass-derived feedstocks has a critical dependence on the molecular structure of the organic and its adsorption on the electrode surface. In this study, we investigated the role of functional groups in the adsorption of the organic molecule on the charged Pd (111) surface and its subsequent effect on organic reduction in electrochemical hydrogenation of organic molecules. With three aromatic carbonyls of benzaldehyde (BZD), acetophenone (ACE), and vanillin (VAN), we rationalize molecular-scale adsorption and interfacial charge transfer processes by employing density-functional-theory based ab initio molecular dynamics simulations. We observe that the functional group and electrode charge strongly affect the proximity of organic molecule to the Pd (111) surface, where distances of aromatic ring and carbonyl group of the organic on the electrode change distinctively with functional groups and charge state of electrode, which strongly impact reduction of organics on the surface. Calculations of differential electron density show the strongest reduction with benzaldehyde via interfacial electron transfer from the charged Pd surface. We also observe that the interaction between the functional groups and solvent (VAN > BZD > ACE) significantly influence the organic interaction with the charged electrode (BZD > VAN > ACE), resulting in the net interaction energy between the organic and the electrode in the order of BZD > ACE > VAN. Experimental measurement of ECH rate also show the same trend of the net interaction energy. These results demonstrate the significance of solvent effect on the reducibility of organic molecules on electrodes.

36 MATERIALS SCIENCE↗
DOE OSTI2022

High-throughput nuclear resonance time domain interferometry using annular slits

Nuclear resonance time domain interferometry (NR-TDI) is used to study the slow dynamics of liquids (that do not require Mössbauer isotopes) at atomic and molecular length scales. Here the TDI method of using a stationary two-line magnetized 57 Fe foil as a source and a stationary single-line stainless steel foil analyzer is employed. The new technique of adding an annular slit in front of a single silicon avalanche photodiode detector enables a wide range of momentum transfers (1 to 100 nm -1 by varying the distance between the annular slits and sample) with a high count rate of up to 160 Hz with a Δ q resolution of ±1.7 nm -1 at q = 14 nm -1 . The sensitivity of this method in determining relaxation times is quantified and discussed. The Kohlrausch–Williams–Watts (KWW) model was used to extract relaxation times for glycerol. These relaxation times give insight into the dynamics of the electron density fluctuations of glycerol as a function of temperature and momentum transfers.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Exact constraints and appropriate norms in machine-learned exchange-correlation functionals

Machine learning techniques have received growing attention as an alternative strategy for developing general-purpose density functional approximations, augmenting the historically successful approach of human-designed functionals derived to obey mathematical constraints known for the exact exchange-correlation functional. More recently, efforts have been made to reconcile the two techniques, integrating machine learning and exact-constraint satisfaction. We continue this integrated approach, designing a deep neural network that exploits the exact constraint and appropriate norm philosophy to de-orbitalize the strongly constrained and appropriately normed (SCAN) functional. The deep neural network is trained to replicate the SCAN functional from only electron density and local derivative information, avoiding the use of the orbital-dependent kinetic energy density. The performance and transferability of the machine-learned functional are demonstrated for molecular and periodic systems.

Artificial neural networks↗
DOE OSTI2020

Charge transfer driven by ultrafast spin transition in a CoFe Prussian blue analogue

Photoinduced charge-transfer is an important process in nature and technology and is responsible for the emergence of exotic functionalities, such as magnetic order for cyanide-bridged bimetallic coordination networks. Despite its broad interest and intensive developments in chemistry and material sciences, the atomic-scale description of the initial photoinduced process, which couples intermetallic charge-transfer and spin transition, has been debated for decades; it has been beyond reach due to its extreme speed. In this work we study this process in a prototype cyanide-bridged CoFe system by femtosecond X-ray and optical absorption spectroscopies, enabling the disentanglement of ultrafast electronic and structural dynamics. Our results demonstrate that it is the spin transition that occurs first on the Co site within ~50 fs, and it is this that drives the subsequent Fe-to-Co charge-transfer within ~200 fs. This study represents a step towards understanding and controlling charge-transfer-based functions using light.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗