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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 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Discovery of Graphene-Water Membrane Structure: Toward High-Quality Graphene Process

It is widely accepted that solid-state membranes are indispensable media for the graphene process, particularly transfer procedures. But these membranes inevitably bring contaminations and residues to the transferred graphene and consequently compromise the material quality. This study reports a newly observed free-standing graphene-water membrane structure, which replaces the conventional solid-state supporting media with liquid film to sustain the graphene integrity and continuity. Experimental observation, theoretical model, and molecular dynamics simulations consistently indicate that the high surface tension of pure water and its large contact angle with graphene are essential factors for forming such a membrane structure. More interestingly, water surface tension ensures the flatness of graphene layers and renders high transfer quality on many types of target substrates. This report enriches the understanding of the interactions on reduced dimensional material while rendering an alternative approach for scalable layered material processing with ensured quality for advanced manufacturing.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Membrane Proteins Have Distinct Fast Internal Motion and Residual Conformational Entropy

Abstract The internal motions of integral membrane proteins have largely eluded comprehensive experimental characterization. Here the fast side‐chain dynamics of the α‐helical sensory rhodopsin II and the β‐barrel outer membrane protein W have been investigated in lipid bilayers and detergent micelles by solution NMR relaxation techniques. Despite their differing topologies, both proteins have a similar distribution of methyl‐bearing side‐chain motion that is largely independent of membrane mimetic. The methyl‐bearing side chains of both proteins are, on average, more dynamic in the ps–ns timescale than any soluble protein characterized to date. Accordingly, both proteins retain an extraordinary residual conformational entropy in the folded state, which provides a counterbalance to the absence of the hydrophobic effect. Furthermore, the high conformational entropy could greatly influence the thermodynamics underlying membrane‐protein functions, including ligand binding, allostery, and signaling.

O'Brien, Evan S.↗
DOE OSTI2023

Understanding the performance of membrane for direct air capture of CO 2

Abstract Direct air capture (DAC) of CO 2 is becoming increasingly important for reducing greenhouse gas concentrations in the atmosphere. However, the cost and energy requirements associated with DAC make it less economically feasible than carbon capture from flue gases. While various methods like solid sorbents and gas–liquid absorption have been explored for DAC, membrane processes have only recently been investigated. The objective of this study is to examine the separation performance of a membrane unit for capturing CO 2 from ambient air. The performance of a membrane depends on several factors, including the composition of the feed gas, pressure ratio, material selectivity, and membrane area. The single‐stage separation process with the co‐current flow and constant permeability flux model is evaluated using a commercial module integrated with a process simulator to separate a binary mixture of carbon dioxide and nitrogen to assess the sensitivity of selectivity on purity and recovery of CO 2 in permeate, and power requirement. Additionally, three levels of CO 2 reduction from the feed stream to the retentate stream (25%, 50%, and 75%) are studied. A trade‐off between purity and recovery factor is observed, and achieving high purity in permeate requires high concentration in the retentate.

Panja, Palash↗
DOE OSTI2021

Prebiotic Membranes and Micelles Do Not Inhibit Peptide Formation During Dehydration

Abstract Cycles of dehydration and rehydration could have enabled formation of peptides and RNA in otherwise unfavorable conditions on the early Earth. Development of the first protocells would have hinged upon colocalization of these biopolymers with fatty acid membranes. Using atomic force microscopy, we find that a prebiotic fatty acid (decanoic acid) forms stacks of membranes after dehydration. Using LC‐MS‐MS (liquid chromatography‐tandem mass spectrometry) with isotope internal standards, we measure the rate of formation of serine dipeptides. We find that dipeptides form during dehydration at moderate temperatures (55 °C) at least as fast in the presence of decanoic acid membranes as in the absence of membranes. Our results are consistent with the hypothesis that protocells could have formed within evaporating environments on the early Earth.

Cohen, Zachary R.↗
DOE OSTI2020

Surface modification of ZIF ‐90 with triptycene for enhanced interfacial interaction in mixed‐matrix membranes for gas separation

Abstract Zeolite imidazole framework (ZIF‐90) nanoparticles were chemically modified by grafting triptycene moieties. The modified nanoparticles were introduced into a triptycene‐based polyimide as fillers to generate mixed matrix membranes (MMMs) for gas separation. The incorporation of “hook‐like” triptycene moieties in both dispersed and continuous phases led to intimate contact between the two phases and thus defect‐free interfacial morphology, due to the supramolecular interlocking and π–π stacking interaction between triptycene units presented in both phases. The filler/polymer solution showed shear thickening behavior due to such strong interfacial interaction. The separation performance of the prepared composite membranes was investigated as a function of filler loading and particle surface grafting density. Pure‐gas permeation results showed that the gas permeabilities increased expectedly as the filler loading increased, with stable or improved selectivities. The reduced permeability relative to pristine polyimide film is likely due to the pore blockage of ZIF‐90 upon grafting triptycene moieties on the particle surface. Reducing the grafting density of triptycene moieties led to improved permeability and selectivity suggesting good tunability of this series of new composite membranes. Overall, modification of nanofiller with hierarchical triptycene moieties offers a fundamentally new avenue for creation of composite membranes with unique properties in gas separations.

Zhang, Qinnan↗
DOE OSTI2020

Recent advances in polymeric facilitated transport membranes for carbon dioxide separation and hydrogen purification

Membrane and membrane process have been widely considered as one of the best candidates for mitigating CO 2 emissions from the combustion or utilization of fossil fuels. Various amine-containing polymers constitute an important class of membranes, where the highly selective CO 2 transport is achieved by the facilitated transport mechanism. In this review, the amine–CO 2 chemistry is discussed in conjunction with the mechanism of the reaction-mediated CO 2 transport. A wide variety of amine-containing polymers are discussed based on two synthesis motifs: (a) polyamines with amino groups covalently bound to the polymer backbone and (b) small molecule amines embedded in a polymer matrix. This review concludes with the remarks on the facilitated transport membranes for post-combustion carbon capture (CO 2 /N 2 ) and hydrogen purification (CO 2 /H 2 ).

42 ENGINEERING↗
DOE OSTI2022

Molecular simulations and NMR reveal how lipid fluctuations affect membrane mechanics

Lipid bilayers form the main matrix of functional cell membranes, and their dynamics underlie a host of physical and biological processes. Here we show that elastic membrane properties and collective molecular dynamics (MD) are related by the mean-square amplitudes (order parameters) and relaxation rates (correlation times) of lipid acyl chain motions. We performed all-atom MD simulations of liquid-crystalline bilayers that allow direct comparison with carbon-hydrogen (CH) bond relaxations measured with NMR spectroscopy. Previous computational and theoretical approaches have assumed isotropic relaxation, which yields inaccurate description of lipid chain dynamics and incorrect data interpretation. Instead, the new framework includes a fixed bilayer normal (director axis) and restricted anisotropic motion of the CH bonds in accord with their segmental order parameters, enabling robust validation of lipid force fields. Simulated spectral densities of thermally excited CH bond fluctuations exhibited well-defined spin-lattice (Zeeman) relaxations analogous to those in NMR measurements. Their frequency signature could be fit to a simple power-law function, indicative of nematic-like collective dynamics. Moreover, calculated relaxation rates scaled as the squared order parameters yielding an apparent K C modulus for bilayer bending. Our results show a strong correlation with K C values obtained from solid-state NMR studies of bilayers without and with cholesterol as validated by neutron spin-echo measurements of membrane elasticity. The simulations uncover a critical role of interleaflet coupling in membrane mechanics and thus provide important insights into molecular sites of emerging elastic properties within lipid bilayers.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Effect of constitutive law on the erythrocyte membrane response to large strains

Three constitutive laws, that is the Skalak, neo-Hookean and Yeoh laws, commonly employed for describing the erythrocyte membrane mechanics are theoretically analyzed and numerically investigated to assess their accuracy for capturing erythrocyte deformation characteristics and morphology. In this work, particular emphasis is given to the nonlinear deformation regime, where it is known that the discrepancies between constitutive laws are most prominent. Hence, the experiments of optical tweezers and micropipette aspiration are considered here, for which relationships between the individual shear elastic moduli of the constitutive laws can also be established through analysis of the tension-deformation relationship. All constitutive laws were found to adequately predict the axial and transverse deformations of a red blood cell subjected to stretching with optical tweezers for a constant shear elastic modulus value. As opposed to Skalak law, the neo-Hookean and Yeoh laws replicated the erythrocyte membrane folding, that has been experimentally observed, with the trade-off of sustaining significant area variations. For the micropipette aspiration, the suction pressure-aspiration length relationship could be excellently predicted for a fixed shear elastic modulus value only when Yeoh law was considered. Importantly, the neo-Hookean and Yeoh laws reproduced the membrane wrinkling at suction pressures close to those experimentally measured. None of the constitutive laws suffered from membrane area compressibility in the micropipette aspiration case.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2021

Subtle penetrant size effects on separation of carbon molecular sieve membranes derived from $\mathrm{6FDA:BPDA}$-$\mathrm{DAM}$ polyimide

Economically scalable carbon molecular sieve (CMS) hollow fiber membranes rely upon a tunable bimodal pore morphology to separate gas pairs using angstrom-level size discrimination. Freshly formed CMS membranes experience self-retarding physical aging, reflected by permeance losses and selectivity gains that stabilize over short times compared to the lifetime of the membrane. Self-retarding morphology rearrangements are of special interest here due to tightening of the largest size range of ultramicropores, thereby causing aging for polyimide-derived CMS. We report effects of such aging for two A/B penetrant pairs, C 3 H 6 /C 3 H 8 and CO 2 /CH 4 . These two pairs not only have different average sizes, $\overline{d}_{A/B}$, but also different size differences,Δd A/B , between the members in each pair. We focus primarily on the C 3 H 6 /C 3 H 8 pair, which is the most difficult of the two pairs to separate, and use some CO 2 /CH 4 results as a comparison case. We study CMS derived from 6FDA:BPDA-DAM (1:1) polyimide by pyrolysis at 550 °C, 600 °C and 650 °C. Here we suggest conditions and physical causes that expedite, retard or even suppress the aging process within CMS membranes. Finally, we suggest how analysis of CMS derived from other precursors and other penetrant pairs can be generalized by understanding the results for the 6FDA:BPDA-DAM (1:1) polyimide derived CMS.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Monitoring pipeline integrity of underground gas storage facilities using membrane-based electrochemical sensors

Effective monitoring of internal corrosion risk is crucial to ensuring the safety and longevity of natural gas pipeline infrastructure. While electrochemical sensors are commonly used to assess corrosion rates and corrosion indicators in aqueous fluids, they are rarely used in gas pipelines as these fluids lack the ionic conductivity needed for electrochemical measurements. The inclusion of ion-conductive membranes into electrochemical sensors can extend their functionality into humidified gas streams, providing critical information about emerging corrosion events that are common during withdrawal season in pipeline systems downstream from underground storage facilities. In parallel, new protective films, like those obtained through cold spray coating, are being developed to protect oil and gas pipelines and recover losses in structural integrity due to corrosion damage. Herein, we demonstrate how membrane-based electrochemical sensors (MBES) can be used to monitor fluid corrosivity by examining their response to changes in water content for a wide range of fluid compositions. It was found that MBES readings were highly sensitive to water content changes with membrane conductivity measurements varying from 10 –6 to 10 –1 S cm -1 , and corrosion rate measurements which varied from 10 –7 to 1 mm y -1 . Electron microscopy confirmed that the self-healing characteristics of metal coating films were still active despite their inclusion into an MBES probe. In conclusion, these findings indicate that membrane-based corrosion monitoring can be expanded to monitor coated-pipeline materials and provide early detection of emerging corrosion upsets relevant to underground gas storage facilities.

Electrochemical sensor↗
DOE OSTI2025

Using X-ray radiography to study oxygen flow in a proton exchange membrane electrolyzer operating under balanced pressure conditions

Of the various water electrolyzer technologies, the proton exchange membrane electrolyzer (PEMWE) is one of the best solutions for producing clean hydrogen without releasing CO 2 . In order to allow for widespread use of clean hydrogen, it is necessary to decrease its cost, which is intrinsically related to system operation. Current PEMWE plants operate in differential mode, directly pressurizing hydrogen and benefiting from thermodynamic compression, which increases overall system efficiency. However, high differential pressure above 30 bar can cause membrane stress, resulting in membrane creeping and failure. Pressurizing the water and operating at balanced pressure allows hydrogen to be produced at higher pressures while preserving the integrity of the membrane and porous layers. Nevertheless, the impact of pressurizing water on PEMWE performance must be better understood to maximize performance under balanced pressure conditions. Here, this study examined the impact of water pressure on two-phase flow. A high-pressure electrolyzer setup was developed to perform operando X-ray radiography and examine oxygen transport with high temporal resolution. The imaging segmentation process, developed to capture bubble properties in the channel, was applied to a specific experiment. The results clearly showed that as pressure increased up to 30 bars, the initial bubbly flow transitioned to slug flow, which led to channel saturation with oxygen. This work demonstrates that two-phase flow in an electrolyzer can be studied using X-ray radiography, which has the advantages of fast measurements and the ability to probe dense materials, such as those required for pressurized electrolyzers.

Balanced high pressure operation↗
DOE OSTI2025

Analysis of anion exchange membrane water electrolyzer performance and its evolution over time

Understanding water, evolved gas, and ionic transport in membrane-electrode-assemblies (MEAs) is essential for the development of high performance and durable anion exchange membrane water electrolyzers (AEMWEs). This study evaluates the MEA conditioning process, operating conditions, and short-term stability in a 1 M potassium hydroxide (KOH) electrolyte, focusing on the underlying transport phenomena. We observe a significant initial voltage loss in continuous cell operation, which could be associated with gas bubble accumulation, transport layer or flow field passivation, and changes in the catalyst oxidation state. Further, we investigate the effects of materials and operational configurations, including the membrane type and thickness, and the electrolyte flow rate, including KOH being fed to both electrodes as well as to the anode only. Furthermore, the effect of membrane drying temperature on ex situ as well as in situ electrochemical performance is evaluated. Finally, we discuss 700 h of AEMWE operation at 1 A/cm 2 , highlighting the underlying degradation phenomena.

25 ENERGY STORAGE↗
DOE OSTI2020

Pattern formation in a coupled membrane-bulk reaction-diffusion model for intracellular polarization and oscillations

Reaction-diffusion systems have been widely used to study spatio-temporal phenomena in cell biology, such as cell polarization. Coupled bulk-surface models naturally include compartmentalization of cytosolic and membrane-bound polarity molecules. Here we study the distribution of the polarity protein Cdc42 in a mass-conserved membrane-bulk model, and explore the effects of diffusion and spatial dimensionality on spatio-temporal pattern formation. We first analyze a one-dimensional (1-D) model for Cdc42 oscillations in fission yeast, consisting of two diffusion equations in the bulk domain coupled to nonlinear ODEs for binding kinetics at each end of the cell. In 1-D, our analysis reveals the existence of symmetric and asymmetric steady states, as well as anti-phase relaxation oscillations typical of slow-fast systems. We then extend our analysis to a two-dimensional (2-D) model with circular bulk geometry, for which species can either diffuse inside the cell or become bound to the membrane and undergo a nonlinear reaction-diffusion process. We also consider a nonlocal system of PDEs approximating the dynamics of the 2-D membrane-bulk model in the limit of fast bulk diffusion. In all three model variants we find that mass conservation selects perturbations of spatial modes that simply redistribute mass. In 1-D, only anti-phase oscillations between the two ends of the cell can occur, and in-phase oscillations are excluded. In higher dimensions, no radially symmetric oscillations are observed. Instead, the only instabilities are symmetry-breaking, either corresponding to stationary Turing instabilities, leading to the formation of stationary patterns, or to oscillatory Turing instabilities, leading to traveling and standing waves. Codimension-two Bogdanov—Takens bifurcations occur when the two distinct instabilities coincide, causing traveling waves to slow down and to eventually become stationary patterns. Our work clarifies the effect of geometry and dimensionality on behaviors observed in ma.ss-conserved cell polarity models.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2025

Membrane protein reconstitution : New possibilities for structural biology, biophysical methods, and antibody/drug discovery

Nearly one-third of all proteins in eukaryotes are membrane proteins. Moreover, roughly 60% of Food and Drug Adminstration (FDA)-approved small-molecule drugs act on membrane proteins, which includes G protein–coupled receptors (GPCRs), ion channels, and transporters. Here, the vast majority of these membrane proteins are cell-surface accessible and thus amenable to drug discovery. At the same time, they are considerably more challenging to reconstitute and prepare for structure initiatives, antibody discovery, and drug screening. This series of reviews introduces the reader to current reconstitution systems, biophysical characterization of the membrane proteins and associated lipids, and common applications involving nuclear magnetic resonance (NMR), mass spectrometry (MS), and cryo-electron microscopy (cryo-EM).

36 MATERIALS SCIENCE↗
DOE OSTI2022

Theoretical Pathway toward Improved Reverse Osmosis Membrane Selectivity for Neutral Solutes: Inspiration from Gas Separations

We report highly rigid membrane materials with tailored structures have exhibited permeabilities and selectivities that exceed the polymer upper bound in gaseous and organic solvent separations for challenging mixtures containing species that are similar in size and shape. One potential question is whether such membrane materials can maintain meaningful guest diffusivities in situations where the microporous spaces are essentially full of guest molecules. Here, we use a simplified transition state theory approach to estimate the diffusivity of water and small organics within a microporous membrane. The transition state theory model is parameterized using experimental values from zeolites and carbon molecular sieve materials found in the literature. We demonstrate the differences in transport and Maxwell–Stefan diffusivities based on guest species loading with different isotherm behaviors. These calculations theorize a path forward for highly selective reverse osmosis membranes for aqueous phase separations.

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

The Role of Water Volume Fraction on Water Adsorption in Anion Exchange Membranes

Water absorption plays a key role in the performance of polymeric anion exchange membranes. It influences important properties such as ionic conductivity and mechanical strength and alters their performance as solid electrolytes in hydrogen electrochemical devices for energy conversion. However, computational approaches that address the relationship between the polymer design and the absorption process are scarce. In this work, we introduce a simple thermodynamic model to predict the water absorption isotherms of polyelectrolyte membranes in contact with a water vapor reservoir that incorporates the specific chemical design of the polymers. The model accurately predicts the water content and macrostructural properties of polynorbornene membranes as a function of the water activity and successfully captures the effect of various polymer design parameters. The energy of pairwise attractive interactions predicted by our model provides a means to interpret the absorption process at the molecular level. The model also reveals the most significant favorable and unfavorable contributions to the free energy and indicates that their balance is solely governed by the water volume fraction, regardless of the polymer design. This universal behavior leads to important implications in the search for better ion exchange membranes.

Zaldivar, Gervasio [New York University, Brooklyn,↗
DOE OSTI2022

Holistic Design Consideration of Metal–Organic Framework-Based Composite Membranes for Lithium–Sulfur Batteries

Metal–organic framework (MOF)-based membranes have received significant attention as separators for lithium–sulfur (Li–S) batteries because of their high porosities, well-defined and tailored structures, and other tunable features that are desirable for preventing the “shuttle effect” of soluble polysulfides. Because of the insulating nature of most MOFs, composite membranes are generally constructed by a combination of MOFs and electron-conductive materials. In this work, we examine the property–performance relation between MOF-based separators and Li–S batteries by systematically adjusting the electrical conductivity, thickness, and mass loading of the MOF-based composite. Beyond the commonly referenced trapping or blocking ability of MOFs toward polysulfides, we find that by fixing the thickness of the MOF-based composite coating layer (~40 μm) on a Celgard membrane, the electrical conductivity of the MOF composite layer is of paramount importance compared with the physical/ chemical trapping ability of polysulfides. However, the trapping ability of MOFs becomes indispensable when the thickness of the composite layer is small (e.g., ~20 μm), indicating the synergetic effects of the adsorption and conversion capabilities of the thin composite layer. Furthermore, this work suggests the importance of a holistic design consideration for a MOF-based membrane for long-life and high-energy-density Li–S batteries.

25 ENERGY STORAGE↗
DOE OSTI2021

Membrane-Induced Vanadium Crossover-Blocking Polybenzimidazole Copolymer with Exceptional Proton Selectivity

Broad deployment of redox flow batteries is hindered, in part, due to the lack of highly selective ion-exchange membranes with high proton conductivity. We report a post-functionalization strategy for polybenzimidazole copolymer (PBI-co) membranes by a reacting mixture of concentrated sulfuric and phosphoric acids that led to improved membrane selectivity while retaining high proton conductivity. Fourier-transform infrared spectroscopy confirmed successful sulfonation and protonation of benzimidazole functionalities. PBI-co exhibits a very high room-temperature proton conductivity of 0.138 S cm -1 , as measured by electrochemical impedance spectroscopy. PBI-co also demonstrates electromigration crossover mitigation under applied current densities up to 500 mA cm -2 , and voltage pulses up to 1.4 V, while also inhibiting diffusion-driven vanadium crossover for over 20 days. Single-cell vanadium flow battery testing on post-functionalized PBI-co further confirms state-of-the-art battery performance with an ~99.5% Coulombic efficiency at 100 mA cm -2 and an area-specific resistance of ~20 mO cm 2 lower than Nafion-212 membrane.

25 ENERGY STORAGE↗