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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 1,171 records · Page 65
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Modeling charge collection efficiency degradation in partially depleted GaAs photodiodes using the 1- and 2-carrier Hecht equations

Here, the Hecht equation can be used to model the nonlinear degradation of charge collection efficiency (CCE) in response to radiation-induced displacement damage in both fully and partially depleted GaAs photodiodes. CCE degradation is measured for laser-generated photocurrent as a function of fluence and bias in Al 0.3 Ga 0.7 As/GaAs/Al 0.25 Ga 0.75 As p-i-n photodiodes which have been irradiated with 12 MeV C and 7.5 MeV Si ions. CCE is observed to degrade more rapidly with fluence in partially depleted photodiodes than in fully depleted photodiodes. When the intrinsic GaAs layer is fully depleted, the 2-carrier Hecht equation describes CCE degradation as photogenerated electrons and holes recombine at defect sites created by radiation damage in the depletion region. If the GaAs layer is partially depleted, CCE degradation is more appropriately modeled as the sum of the 2-carrier Hecht equation applied to electrons and holes generated within the depletion region and the 1-carrier Hecht equation applied to minority carriers that diffuse from the field-free (non-depleted) region into the depletion region. Enhanced CCE degradation is attributed to holes that recombine within the field-free region of the partially depleted intrinsic GaAs layer before they can diffuse into the depletion region.

43 PARTICLE ACCELERATORS↗
DOE OSTI2025

In Situ Observation of Ion Migration in a Ferroelectric Ionic Conductor Rb-KTP during Thermal Annealing

Ion exchange in Rb-doped KTiOPO 4 has facilitated significant advancements in ferroelectric domain engineering, yet understanding the underlying mechanisms remains in its infancy. We perform time-of-flight secondary ion mass spectrometry analysis on multiple periodically ion-exchanged and periodically poled Rb-doped KTiOPO 4 samples under different temperatures and annealing durations. The results are compared between annealing in air, which involved ex situ annealing before periodic poling, and vacuum annealing conducted in situ after periodic poling. The Rb + diffusion profile after periodic ion exchange forms a tooth-shaped pattern. We show that in situ annealing causes a surface pinning effect on the nonpolar face, limiting Rb + migration along the polar axis at the surface. Once the pinned layer is removed through milling, the underlying Rb + diffusion is distinctively different from the surface. Additionally, the rate of Rb + diffusion during in situ annealing is linear, while the periodic domain structures remain stable after annealing. These results contribute to understanding the ionic diffusion process in a ferroelectric ionic conductor and using ion exchange to tailor the linear and nonlinear properties of KTiOPO 4 .

36 MATERIALS SCIENCE↗
DOE OSTI2013

Acoustic Enhancement of Surface Diffusion

The idea of acoustic activation of surface diffusion is explored theoretically and in atomistic simulations. It is found that a substantial diffusion enhancement by surface acoustic waves is possible via (1) transient surface strain-induced modification of the diffusion barriers, (2) adiabatic variation in the surface temperature, and (3) dynamic coupling of the acoustic waves with vibrational states of adsorbed species. The approximate scaling laws describing the first two effects are established and verified in kinetic Monte Carlo simulations. The combined contribution of all three effects is studied in molecular dynamics simulations, and the conditions for the diffusion activation through the dynamic coupling are elucidated. The acoustic enhancement of surface diffusion provides an attractive alternative to thermal activation in thin film growth on heat-sensitive substrates.

Chemistry↗
DOE OSTI2011

Diffusive ion fluxes in a turbulent plasma

Ion kinetic equations are discussed in the context of the ion acoustic turbulence model, which provides an intrinsically noncontradictory description of strong heating of the plasma components. For such plasma heating by a strong constant electric field, nonstationary diffusive fluxes across the confining magnetic field are calculated that are due to induced scattering of ion acoustic waves by ions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Catalytic and Transport Behaviors of Model and Porous and Composite Nanostructures

As stressed in the Basic Energy Sciences Advisory Committee (BESAC) Report “New Science for a Secure and Sustainable Energy Future” (December 2008), solving our Nation’s energy challenges will entail more than incremental changes in present materials-related technologies; new, advanced routes to nanostructured materials with transformational properties will be required. Herein we describe the design and fabrication of a hybrid biotic/abiotic membrane reactor that, mimicking natural systems, employs the metalloenzyme, carbonic anhydrase, to separate CO 2 from N 2 with unprecedented purity and rate. The membrane design, synthesis, and operation are based on multiple biomimetic and nanoscale fabrication strategies, nanoscale dimensional features, and nanoscale physical phenomena, for example: 1) Bottom-up self-assembly of a membrane comprising a periodic, aligned, cylindrical nanopore array with 8 nm diameter pores designed to accommodate carbonic anhydrase (CA) enzymes 2) Top-down Atomic Layer Deposition (ALD) and plasma processing of the nanopore array to create 18nm deep (by 8nm in diameter) superhydrophilic pores bounded by hydrophobic/superhydrophobic interfaces 3) Formation of a continuous, defect free, ultra-thin (~18-nm thick) but strong water membrane by capillary condensation within the uniformly-sized, superhydrophilic nanopore array 4) Accommodation of CA within the water filled nanopore array (~2 CAs per hydrophilic pore channel) to achieve an effective CA concentration within the 18-nm thick water membrane over 10X greater than achievable in solution Exposed to a mixture of CO 2 and N 2 this biomimetic membrane rapidly and selectively dissolves CO 2 within the CA filled water nano-channels on the ‘upstream side’ and regenerates CO 2 at the superhydrophobic interface on the ‘downstream’ side. In combination, the high CA concentration and exceptionally short diffusion distances enable rapid and highly selective CO 2 separation from N 2 and H 2 . Our membrane has a combined CO 2 flux and selectivity that exceed by orders of magnitude all existing CO 2 membranes and for the first time meet the US Department of Energy guidelines for CO 2 sequestration technologies. (The performance of our membrane was recognized by an R&D100 Award and the first R&D100 Green Technology Award in 2015 and an issued US Patent in 2017). We believe this membrane could be employed in combination with sequestration to help reduce greenhouse gas emissions and provide a viable, economically feasible pathway to achieve the goals of the 2016 Paris Accord, which aims to maintain a global temperature rise this century less than 2°C above pre-industrial levels. Further this membrane concept could be adapted to other enzymes to accomplish other separations of interest, e.g. H 2 . We also have established processing-structure-property relationships of ultrathin membrane-like monolayer materials that are intrinsically catalytic. Establishing processing-structure-property relationships for monolayer materials is crucial for a vast range of applications spanning optics, catalysis, electronics, and energy. Presently, for MoS 2 , a promising catalyst for artificial photosynthesis, considerable debate surrounds the structure/property relationships of its various allotropes. Using high-resolution transmission electron microscopy supported by density functional theory, we unambiguously solved the structure of MoS 2 monolayers and showed lithium intercalation to direct a preferential transformation of the basal plane from 2H (trigonal prismatic) to 1T’ (clustered Mo). These changes alter the energetics of MoS 2 interactions with hydrogen ((GH), and, with respect to catalysis, the 1T’ transformation renders the normally inert basal plane amenable towards hydrogen adsorption and H 2 evolution achieving Hydrogen Evolution Reaction (HER) catalytic activity comparable to 2H MoS 2 edges on Au(111), one of the most active HER catalysts known.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2025

Be₂C as a neutron moderator for molten salt reactors: A first-principles study of structural, electronic, and defect properties

Beryllium carbide (Be 2 C), valued for its high neutron moderation efficiency and low absorption cross section, is a promising high-temperature neutron moderator for molten salt reactors. Its practical adoption, however, demands significant technological maturation, requiring comprehensive theoretical and experimental studies of its response to different conditions, including high temperature and irradiation. Here, we report initial results on the fundamental properties and radiation-induced defects of Be 2 C, focusing on antisites, vacancies, interstitial atoms, and Frenkel pairs in the Be and C sublattices. Using density functional theory (DFT) and ab initio molecular dynamics (AIMD), we calculate the defects formation and binding energies, evaluating their dependence on the supercell size, charge states, and chemical environment. In general, carbon defects exhibit higher formation energies, greater sensitivity to cell size, and stronger impacts on the density of states compared to beryllium defects, with charged state the effects being more pronounced. Static DFT reveals multiple metastable interstitial configurations, while AIMD identifies ground states as C-C <100> dumbbells and octahedral Be interstitials. In conclusion, the diversity of metastable configurations and defect states complicates the diffusion mechanisms, requiring further molecular dynamics analysis to elucidate the mechanisms and rates of radiation-induced atomic transport, as well as the structural stability of Be2C.

Ab initio modeling↗
DOE OSTI2015

Profile stiffness measurements in the Helically Symmetric experiment and comparison to nonlinear gyrokinetic calculations

Stiffness measurements are presented in the quasi-helically symmetric experiment (HSX), in which the neoclassical transport is comparable to that in a tokamak and turbulent transport dominates throughout the plasma. Electron cyclotron emission is used to measure the local electron temperature response to modulated electron cyclotron resonant heating. The amplitude and phase of the heat wave through the steep electron temperature gradient (ETG) region of the plasma are used to determine a transient electron thermal diffusivity that is close to the steady-state diffusivity. The low stiffness in the region between 0.2 ≤ r/a ≤ 0.4 agrees with the scaling of the steady-state heat flux with temperature gradient in this region. These experimental results are compared to gyrokinetic calculations in a flux-tube geometry using the gyrokinetic electromagnetic numerical experiment code with two kinetic species. Linear simulations show that the ETG mode may be experimentally relevant within r/a ≤ 0.2, while the Trapped Electron Mode (TEM) is the dominant long-wavelength microturbulence instability across most of the plasma. The TEM is primarily driven by the density gradient. Non-linear calculations of the saturated heat flux driven by the TEM and ETG bracket the experimental heat flux.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Advances and prospects to achieve high-performing and durable proton-exchange-membrane unitized regenerative fuel cells

Proton-exchange-membrane unitized regenerative fuel cell (PEM-URFC) is a promising energy storage and conversion device for large-scale and long-term applications. Previous research has primarily focused on materials development studies, with performance and durability not evaluated at relevant conditions. Such an approach becomes insufficient for making URFC technology commercially competitive. In this review, we highlight recent progress on high-performing PEM-URFCs, focusing on electrode engineering, key components, and operating approaches that take realistic operating conditions into consideration. Key components of a membrane electrode assembly (MEA), including catalyst layer, diffusion media, and membrane, which require different optimization strategies, are discussed in this review.

25 ENERGY STORAGE↗
DOE OSTI2025

Adaptive Interface-PINNs (AdaI-PINNs) for inverse problems: Determining material properties for heterogeneous systems

Here, we determine spatially varying discontinuous material properties using a domain-decomposition based physics-informed neural networks (PINNs) framework named the Adaptive Interface-PINNs or AdaI-PINNs (Roy et al., 2024). We propose the use of distinct neural networks for the field variables and material properties within each material, utilizing adaptive activation functions. While the neural networks across different materials share the same weights and biases, their activation functions are uniquely tailored using a hyperparameter that influences the slope of the activation function. The proposed framework is tested on several one-dimensional and two-dimensional benchmark examples, and its performance is compared with conventional PINNs and existing domain-decomposition PINNs frameworks, namely, the Multi-domain physics-informed neural network (M-PINN), and the eXtended physics-informed neural networks (XPINNs). The results demonstrate that the proposed approach can determine randomly distributed discontinuous material properties with an L 2 error of $\mathscr{O}$ (10 -3 ) for the material property and the root-mean-square error of $\mathscr{O}$ (10 -3 ) for the primary variable while the other approaches yield errors that are approximately two orders of magnitude larger (that is, $\mathscr{O}$ (10 -1 )). Moreover, the spatial distribution of material properties obtained using the proposed framework is in close agreement with the true distribution, whereas the other approaches fare much worse. Additionally, the proposed approach is approximately 40% faster than its competitors, indicating its potential as a robust alternative for solving inverse problems in heterogeneous materials.

36 MATERIALS SCIENCE↗
DOE OSTI2019

A multi-modal sweat sensing patch for cross-verification of sweat rate, total ionic charge, and Na + concentration

Sweat sensors introduced in recent years have targeted a variety of sweat features and biomarkers for non-invasive health monitoring. Amongst these targets, reliable monitoring of sweat rate is crucial due to its modulation of sweat analyte concentrations and its intrinsic significance to numerous medical and physiological health conditions. In this paper, we present a sweat rate sensor structure comprising of electrodes with interdigitated fingers in a microfluidic channel. Each time the accumulating sweat impinges on an electrode finger, the sensor reports a jump in admittance that can be simply and efficiently counted to estimate sweat rate, overcoming selectivity limitations of previously reported sweat rate sensors. We further integrate an impedimetric sensor for measuring total ionic charge concentration and an electrochemical Na + sensor, together creating a multi-modal system for analyzing fluid and electrolyte secretion. We demonstrate how low analyte diffusion rates through this microfluidic device allow for multi-purpose sensor function, including utilizing the sweat rate sensor signal to corroborate total ionic sensor measurements. This cross-verification capability ensures data integrity in real time, satisfying a vital consideration for personalized healthcare technologies. We use the presented patch for continuous analysis of sweat rate, total ionic charge concentration, and Na + concentration during exercise, while demonstrating how multi-modal cross-verification brings new trust to sensor readings.

47 OTHER INSTRUMENTATION↗
DOE OSTI2014

The double well mass filter

Various mass filter concepts based on rotating plasmas have been suggested with the specific purpose of nuclear waste remediation. We report on a new rotating mass filter combining radial separation with axial extraction. The radial separation of the masses is the result of a “double-well” in effective radial potential in rotating plasma with a sheared rotation profile.

42 ENGINEERING↗
DOE OSTI2019

How Microstructure and Pore Moisture Affect Strength Gain in Portlandite-Enriched Composites That Mineralize CO 2

Binders containing portlandite (Ca(OH) 2 ) can take up carbon dioxide (CO 2 ) from dilute flue gas streams (<15% CO 2 , v/v), thereby forming carbonate compounds with binding attributes. While the carbonation of portlandite particulates is straightforward, it remains unclear how CO 2 transport into monoliths is affected by microstructure and pore moisture content. Therefore, this study elucidates the influences of pore saturation and CO 2 diffusivity on the carbonation kinetics and strength evolution of portlanditeenriched composites (“mortars”). To assess the influences of microstructure, composites hydrated to different extents and conditioned to different pore saturation levels (S w ) were exposed to dilute CO 2 . First, reducing saturation increases the gas diffusivity and carbonation kinetics so long as saturation exceeds a critical value (S w,c ≈ 0.10) independent of microstructural attributes. Second, careful analysis reveals that both traditional cement hydration and carbonation offer similar levels of strengthening, the magnitude of which can be estimated from the extent of each reaction. As a result, portlandite-enriched binders offer cementation performance that is similar to traditional materials while offering an embodied CO 2 footprint that is more than 50 % smaller. Furthermore, these insights are foundational to create new “low-CO 2 ” cementation agents via in situ CO 2 mineralization (utilization) using dilute CO 2 waste streams.

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

A Comprehensive Experimental Study on Microstructure‐Graded Graphite Anodes for Enhancing Fast‐Charging Capability of Lithium‐Ion Batteries

Lithium‐ion batteries with high gravimetric capacity density and improved cycle life performance under fast‐charging conditions are crucial for widespread electric vehicle (EV) adoption. This study investigates how designing graphite anode microstructure, specifically porosity, and particle‐size gradients, improves lithium‐ion (Li + ) transport during fast‐charging conditions. Three‐layered graphite anodes with varying porosity (24%, 36%, 46%) and particle size gradients (3, 5, 10 μm) were compared to a conventional single‐layered electrode in half‐cell configurations. At room temperature and high discharge rate (2C), both gradient structures showed significantly enhanced capacity retention (80% and 67% vs. 50%) compared to the conventional electrode, highlighting the effectiveness of microstructure engineering for fast charging. The study also investigated the temperature's impact on cycle life. After 200 cycles at 2°C and 45°C, all gradient structures demonstrated superior capacity retention (≈80%) compared to the conventional electrode (35%), suggesting the gradients mitigate degradation rate at high temperatures. Electrochemical impedance spectroscopy confirmed superior Li+ diffusion and lower resistivity in gradient electrodes. Simulations explored the influence of gradient profiles on reaction kinetics across the electrode thickness. Overall, this research demonstrates that the fast‐charging capability of graphite electrodes can be greatly enhanced by engineering the electrode microstructure, thereby making EV technology more accessible and appealing.

Ahmadi, Soma↗