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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Exceptional Mineral Scaling Resistance from the Surface Gas Layer: Impacts of Surface Wetting Properties and the Gas Layer Charging Mechanism

Mineral scaling is a phenomenon that occurs on submerged surfaces in contact with saline solutions. In membrane desalination, heat exchangers, and marine structures, mineral scaling reduces process efficiency and eventually leads to process failure. Therefore, achieving long-term scaling resistance is beneficial to enhancing process performance and reducing operating and maintenance costs. While evidence shows that superhydrophobic surfaces may reduce mineral scaling kinetics, prolonged scaling resistance is limited due to the finite stability of the entrained gas layer present in a Cassie–Baxter wetting state. Additionally, superhydrophobic surfaces are not always feasible for all applications, but strategies for long-term scaling resistance with smooth or even hydrophilic surfaces are often overlooked. In this study, we elucidate the role of interfacial nanobubbles on the scaling kinetics of submerged surfaces of varied wetting properties, including those that do not entrain a gas layer. We show that both solution conditions and surface wetting properties that promote interfacial bubble formation enhances scaling resistance. In the absence of interfacial bubbles, scaling kinetics decrease as surface energy decreases, while the presence of bulk nanobubbles enhances the scaling resistance of the surface with any wetting property. The findings in this study allude to scaling mitigation strategies that are enabled by solution and surface properties that promote the formation and stability of interfacial gas layers and provide insights to surface and process design for greater scaling resistance.

calcite↗
DOE OSTI2025

Is There a Scalar Atmospheric Surface Layer Within a Convective Boundary Layer? Implications for Flux Measurements

Top‐down entrainment shapes the vertical gradients of sensible heat, latent heat, and CO 2 fluxes, influencing the interpretation of eddy covariance (EC) measurements in the unstable atmospheric surface layer (ASL). Using large eddy simulations for convective boundary layer flows, we demonstrate that decreased temperature gradients across the entrainment zone increase entrainment fluxes by enhancing the entrainment velocity, amplifying the asymmetry between top‐down and bottom‐up flux contributions. These changes alter scalar flux profiles, causing flux divergence or convergence and leading to the breakdown of the constant flux layer assumption (CFLA) in the ASL. As a result, EC‐measured fluxes either underestimate or overestimate “true” surface fluxes during divergence or convergence phases, contributing to energy balance non‐closure. The varying degrees of the CFLA breakdown are a fundamental cause for the non‐closure issue. These findings highlight the underappreciated role of entrainment in interpreting EC fluxes, addressing non‐closure, and understanding site‐to‐site variability in flux measurements.

eddy covariance fluxes of scalars↗
DOE OSTI2021

Unusual layer-by-layer growth of epitaxial oxide islands during Cu oxidation

Elucidating metal oxide growth mechanisms is essential for precisely designing and fabricating nanostructured oxides with broad applications in energy and electronics. However, current epitaxial oxide growth methods are based on macroscopic empirical knowledge, lacking fundamental guidance at the nanoscale. Using correlated in situ environmental transmission electron microscopy, statistically-validated quantitative analysis, and density functional theory calculations, we show epitaxial Cu 2 O nano-island growth on Cu is layer-by-layer along Cu 2 O(110) planes, regardless of substrate orientation, contradicting classical models that predict multi-layer growth parallel to substrate surfaces. Growth kinetics show cubic relationships with time, indicating individual oxide monolayers follow Frank-van der Merwe growth whereas oxide islands follow Stranski-Krastanov growth. Cu sources for island growth transition from step edges to bulk substrates during oxidation, contrasting with classical corrosion theories which assume subsurface sources predominate. Our results resolve alternative epitaxial island growth mechanisms, improving the understanding of oxidation dynamics critical for advanced manufacturing at the nanoscale.

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

Embedding physics domain knowledge into a Bayesian network enables layer-by-layer process innovation for photovoltaics

Process optimization of photovoltaic devices is a time-intensive, trial-and-error endeavor, which lacks full transparency of the underlying physics and relies on user-imposed constraints that may or may not lead to a global optimum. Herein, we demonstrate that embedding physics domain knowledge into a Bayesian network enables an optimization approach for gallium arsenide (GaAs) solar cells that identifies the root cause(s) of underperformance with layer-by-layer resolution and reveals alternative optimal process windows beyond traditional black-box optimization. Our Bayesian network approach links a key GaAs process variable (growth temperature) to material descriptors (bulk and interface properties, e.g., bulk lifetime, doping, and surface recombination) and device performance parameters (e.g., cell efficiency). For this purpose, we combine a Bayesian inference framework with a neural network surrogate device-physics model that is 100× faster than numerical solvers. With the trained surrogate model and only a small number of experimental samples, our approach reduces significantly the time-consuming intervention and characterization required by the experimentalist. As a demonstration of our method, in only five metal organic chemical vapor depositions, we identify a superior growth temperature profile for the window, bulk, and back surface field layer of a GaAs solar cell, without any secondary measurements, and demonstrate a 6.5% relative AM1.5G efficiency improvement above traditional grid search methods.

14 SOLAR ENERGY↗
DOE OSTI2020

The sensitive surface chemistry of Co-free, Ni-rich layered oxides: identifying experimental conditions that influence characterization results

Recent studies have suggested that Co-free, Ni-rich layered cathodes (e.g., doped LiNiO2) can provide promising battery performance for practical applications. However, these layered cathodes suffer from significant surface instability during various stages of the sample history, which generates inherent challenges for achieving stable battery performance and obtaining statistically representative characterization results. To reliably report the surface chemistry of these materials, delicate controls of stepwise sample preparation are required. In this study, we aim to reveal how the surface chemistry of LiNiO2 based materials changes with various environments, including human exhalation, sample storage, sample preparation, electrochemistry cycling, and surface doping. Our results demonstrate that the surface of these materials is highly reactive and prone to alter at various stages of sample handling and characterization. The sensitive surface could impact the interpretation of the surface chemical and structural information, including surface carbonate formation, transition metal reduction and dissolution, and surface reconstruction. Importantly, the heterogeneity of the surface degradation calls for a consolidation of nanoscale, high-resolution characterization, and ensemble-averaged methods in order to improve statistical representation. Furthermore, the doping chemistry can effectively mitigate the surface degradation and improve overall battery performance due to the enhanced surface oxygen retention. Our study highlights the necessity of strict measurements through complementary characterizations at multiple length scales to eliminate unintentional biased conclusions.

surface chemistry, Co-free Ni-rich cathodes, Istab↗
DOE OSTI2020

Chemical approaches to artificial photosynthesis: A molecular, dye-sensitized photoanode for O 2 production prepared by layer-by-layer self-assembly

We describe here the preparation of a family of photoanodes for water oxidation that incorporate an electron acceptor–chromophore–catalyst in single molecular assemblies on nano-indium tin oxide (nanoITO) electrodes on fluorine-doped tin oxide (FTO). The assemblies were prepared by using a layer-by-layer, Atomic Layer Deposition (ALD), self-assembly approach. In the procedure, addition of an electron acceptor viologen derivative followed by a Ru II (bpy) chromophore and a pyridyl derivative of the water oxidation catalyst [Ru(bda) (L) 2 ] (bda = 2,2'-bipyridine-6,6'-dicarboxylate) 2 , were linked by ALD by addition of the bridge precursors TiO 2 , ZrO 2 , and Al 2 O 3 as the bridging groups giving the assemblies, FTO|nanoITO|–MV 2+ –ALD MO 2 –RuP2 2+ –ALD M'O 2 –WOC. In a series of devices, the most efficient gave water oxidation with an incident photon to current efficiency of 2.2% at 440 nm. Transient nanosecond absorption measurements on the assemblies demonstrated that the slow step in the intra-assembly electron transfer is the electron transfer from the chromophore through the viologen bridge to the nanoITO electrode.

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

Synthesis of La 2–x Sr x CuO 4 films via atomic layer-by-layer molecular beam epitaxy

Atomic layer-by-layer molecular beam epitaxy (ALL-MBE) is a sophisticated technique to synthesize high-temperature superconductor (HTS) materials. ALL-MBE produces single-crystal HTS films with atomically smooth surfaces and interfaces, as well as precise multilayer heterostructures engineered down to a single atomic layer level. This enables the fabrication of tunnel junctions, nanowires, nanorings, and other HTS devices of interest. Our group has focused on ALL-MBE synthesis and materials science of La 2–x Sr x CuO 4 (LSCO), a representative HTS cuprate. In the past two decades, we have synthesized over three thousand LSCO thin films and characterized them by a range of analytical techniques. Here, we present in full detail a systematic process for the synthesis and engineering of atomically perfect LSCO films. The procedure includes the preparation of substrates, calibration of the elemental sources, the recipe for ALL growth of LSCO films without any secondary-phase precipitates, post-growth annealing of the films, and ex situ film characterization. This report should aid replication and dissemination of this technique of synthesizing single-crystal LSCO films for basic research as well as for HTS electronic applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Hybridization of Bogoliubov Quasiparticles between Adjacent CuO 2 Layers in the Triple-Layer Cuprate Bi 2 Sr 2 Ca 2 Cu 3 O 10 + δ Studied by Angle-Resolved Photoemission Spectroscopy

Hybridization of Bogoliubov quasiparticles (BQPs) between the CuO 2 layers in the triple-layer cuprate high-temperature superconductor Bi 2 Sr 2 Cu 2 Cu 3 O 10+δ is studied by angle-resolved photoemission spectroscopy (ARPES). In the superconducting state, an anticrossing gap opens between the outer- and inner-BQP bands, which we attribute primarily to interlayer single-particle hopping with possible contributions from interlayer Cooper pairing. We find that the d-wave superconducting gap of both BQP bands smoothly develops with momentum without an abrupt jump in contrast to a previous ARPES study. Hybridization between the BQPs also gradually increases in going from the off nodal to the antinodal region, which is explained by the momentum dependence of the interlayer single-particle hopping. As possible mechanisms for the enhancement of the superconducting transition temperature, the hybridization between the BQPs as well as the combination of phonon modes of the triple CuO 2 layers and spin fluctuations represented by a four-well model are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Layer-by-Layer Nanoarchitectonics of Electrochemically Active Thin Films Comprised of Radical-Containing Polymers

Electroactive coatings based on non-conjugated redox-active polymers have increased in popularity with the development of thin film organic batteries. Here, control over coating deposition, redox-activity, and ion transport are key to improving their energy storage performance. In this work, the synthesis, solution state electrochemical characterization, and layer-by-layer (LbL) assembly of a nitroxide-based polycation and polyanion are presented. Solution state electrochemical characterization indicates that the rate of electron transfer for the nitroxide polyanion is much higher as compared to the nitroxide polycation. LbL thin films of the nitroxide polyanion and nitroxide polycation are assembled, demonstrating linear growth and tunable thickness (28 nm/layer pair). This work confirms that the ion transport mechanism of the LbL films during the redox reaction is influenced depending on the charge of the terminating layer, where the nitroxide polyanion can participate in self-doping, which leads to a contribution from cation transport. The nitroxide polyanion-terminated film also exhibits a higher capacity and a slightly reduced charge transfer resistance. However, it was also observed that a more pronounced capacity fade occurred for the polyanion-terminated film than the polycation-terminated film. Taken together, this highlights how oppositely charged radical-containing polyelectrolytes can form electroactive coatings for possible applications in energy storage or sensing.

25 ENERGY STORAGE↗
DOE OSTI2021

Photonic Curing of Nickel Oxide Transport Layer and Perovskite Active Layer for Flexible Perovskite Solar Cells: A Path Towards High-Throughput Manufacturing

High-throughput roll-to-roll (R2R) manufacturing of perovskite solar cells (PSCs) is currently limited by thermal processes that take tens of minutes each, translating to impractically long annealing tools at high web speeds. In addition, PSCs are usually made with metal oxide transport layer materials that require high temperatures for thermal annealing. Here, we demonstrate the fabrication of PSCs using photonic curing, instead of thermal annealing, to convert NiO x directly from sol-gel precursors for hole transport layers and to crystallize methylammonium lead iodide (MAPbI 3 ) active layers on flexible Willow ® Glass substrates. Photonic curing uses short, intense pulses of light to process materials at a high speed, hence it is compatible with R2R manufacturing. We achieved power conversion efficiencies (PCEs) of 11.7% in forward-scan and 10.9% in reverse-scan for PSCs made with photonic cured NiO x and MAPbI 3 films. Furthermore, both NiO x and MAPbI 3 films could be processed with a single photonic curing pulse, with a web speed of 5.7 m/min, and still produce PCEs comparable to thermally annealed control samples. Based on the single-pulse photonic curing condition for each film, we project a web speed of 26 m/min, laying a pathway to high-throughput production of perovskite solar modules.

14 SOLAR ENERGY↗
DOE OSTI2021

Highly Rectifying Fluidic Diodes Based on Asymmetric Layer-by-Layer Nanofilms on Nanochannel Membranes

Nanochannel-based fluidic diodes display ion selectivity and ion-current rectification (ICR), which may prove important in energy harvesting and biosensors. This paper reports asymmetric functionalization of the outer surface of a flexible nanochannel polymer membrane to create fluidic diodes that give ICR. Layer-by-layer (LbL) adsorption with cross-linking of only the underlying part of the polyelectrolyte nanofilm leads to a porosity step across the film. The combination of a high effective surface-charge density and the porosity step in the film leads to a remarkable maximum ICR factor of ~200 with a pH gradient across the film. Incorporation of pH-sensitive polyelectrolyte components enables the ICR factor to increase an order of magnitude on going from pH 8 to pH 3. Furthermore, the coated membrane shows excellent anion-selectivity. Thus, LbL adsorption with partial cross-linking provides a simple method for creating coated nanochannel membranes that serve as pH-responsive ionic diodes for potential chemical/biosensors.

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

Mild-Annealed Molecular Layer Deposition (MLD) Tincone Thin Film as Photoelectrochemically Stable and Efficient Electron Transport Layer for Si Photocathodes

Metalcone thin films, composed of inorganic–organic hybrids, are synthesized using molecular layer deposition (MLD) through reactions between organometallic precursors (e.g., Sn, Al, and Ti) and organic reactants (e.g., ethylene glycol and glycerol). Despite their unique properties, metalcones exhibit significant vulnerability to water due to their organic components, limiting their potential in electrochemical applications. This study focuses on enhancing the photoelectrochemical stability of tincone thin films in aqueous electrolyte while preserving their hybrid characteristics through mild annealing in air at 250 °C. As-deposited and vacuum-annealed tincone thin films exhibited significant degradation under these conditions, while high-temperature-annealed (500 °C) tincone thin films offered improved stability with a significant decline in charge transfer efficiency. In contrast, mild annealing in air maintained the C–O bond at half level and improved the stability and charge transport without compromising the unique characteristics of tincone. This was confirmed by ellipsometry, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). Mild-annealed tincone deposited on a lightly doped p-type silicon (p-Si) photocathode produced a 20-fold increase in CO volume compared to high-temperature annealed tincone in a CO 2 -saturated potassium bicarbonate (KHCO 3 ) electrolyte with dispersed graphene oxide–cobalt phthalocyanine (GO-CoPc) under 1 sun illumination at 0.9 V vs reversible hydrogen electrode (RHE), while maintaining the faradaic efficiency for CO and H 2 . These results suggest that mild-annealed tincone thin films hold significant potential as protective charge transport layers on silicon photocathodes for the aqueous CO 2 reduction reaction (CO 2 RR).

Annealing (metallurgy)↗
DOE OSTI2025

Nacre-like MXene/Polyacrylic Acid Layer-by-Layer Multilayers as Hydrogen Gas Barriers

MXenes are a promising class of 2D nanomaterials and are of particular interest for gas barrier applications due to their high aspect ratio. However, MXene nanosheets naturally bear a negative charge, which prevents assembly with negatively charged polymers, such as polyacrylic acid (PAA), into gas barrier coatings. Here, we present MXene- and PAA-based layer-by-layer (MXene/ PAA LbL) multilayers formed by leveraging hydrogen bonding interactions. When assembled in acidic conditions, MXene/PAA LbL multilayers exhibit conformal, pinhole-free, nacre-like structures. The MXene/PAA LbL multilayers yield high blocking capability and low permeability (0.14 ± 0.01 cc·mm·m −2 ·day −1 · MPa −1 ) for hydrogen gas which is over 9000 times lower than uncoated niobium (Nb) substrate. These nacre-like structures are also electronically conductive (σ DC , up to 370 ± 30 S cm −1 ). Because these multilayers utilize hydrogen bonding, their properties are highly sensitive to the pH of the assembly and its external environment. Specifically, the reversible deconstruction of these multilayers under basic conditions is experimentally verified. This study shows that hydrogen bonding interactions can be leveraged to form MXene LbL multilayers as gas barriers, electronically conductive coatings, and deconstructable thin films via pH control.

36 MATERIALS SCIENCE↗