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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 OSTI2024

Identifying electrochemical processes by distribution of relaxation times in proton exchange membrane electrolyzers

Distribution of relaxation time (DRT) is used to interpret electrochemical impedance spectroscopy (EIS) for proton exchange membrane (PEM) water electrolyzers, with an attempt to separate overlapped relaxation processes in Nyquist plots. By varying operating conditions and catalyst loadings, four main relaxation peaks arising from EIS can be identified and successfully separated from low to high frequencies as (P1) mass transport, (P2) oxygen evolution reaction kinetics, (P3) reaction kinetics (with faster time constant than P2), and (P4) ionic transport. Here, the shape, height, and frequency of the DRT peaks change with different membrane electrode assembly (MEA) configurations. Electron microscopy reveals distinct features from the cross-sectioned MEAs which verify critical DRT results in that increasing the iridium (Ir)-anode loading from 0.2 mgIr/cm 2 to 1.5 mgIr/cm 2 reduces kinetic losses due to higher site-access; a thick and compacted anode, however, also triggers higher ohmic resistances from membrane/catalyst layer hydration and increases transport losses due to longer ionomer pathways. DRT provides higher resolution to EIS for deconvoluting processes with different relaxation times and the quantification of DRT peaks improves the accounting of total losses from each process.

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

Proton Tunable Analog Transistor for Low Power Computing

This project was broadly motivated by the need for new hardware that can process information such as images and sounds right at the point of where the information is sensed (e.g. edge computing). The project was further motivated by recent discoveries by group demonstrating that while certain organic polymer blends can be used to fabricate elements of such hardware, the need to mix ionic and electronic conducting phases imposed limits on performance, dimensional scalability and the degree of fundamental understanding of how such devices operated. As an alternative to blended polymers containing distinct ionic and electronic conducting phases, in this LDRD project we have discovered that a family of mixed valence coordination compounds called Prussian blue analogue (PBAs), with an open framework structure and ability to conduct both ionic and electronic charge, can be used for inkjet-printed flexible artificial synapses that reversibly switch conductance by more than four orders of magnitude based on electrochemically tunable oxidation state. Retention of programmed states is improved by nearly two orders of magnitude compared to the extensively studied organic polymers, thus enabling in-memory compute and avoiding energy costly off-chip access during training. We demonstrate dopamine detection using PBA synapses and biocompatibility with living neurons, evoking prospective application for brain - computer interfacing. By application of electron transfer theory to in-situ spectroscopic probing of intervalence charge transfer, we elucidate a switching mechanism whereby the degree of mixed valency between N-coordinated Ru sites controls the carrier concentration and mobility, as supported by density functional theory (DFT) .

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2026

Additive-Induced Morphology Change of Polymer Film Enables Enhanced Charge Mobility and Faster Organic Electrochemical Transistor Switching

Conjugated polymers (CPs) play an important role in organic electrochemical transistors (OECTs) for bioelectronics and related applications, where they serve as channel materials. Currently, most successful polymers for CPs are re-engineered from traditional CPs by replacing hydrophobic alkyl side chains with hydrophilic ethylene glycol or ionic groups. Frustratingly, the enhanced ion transport often compromises the charge mobility of the original CP. In this work, we present an additive-mediated method to construct a modified poly(3-hexylthiophene) (P3HT) film to enable efficient ion migration. The additive is designed with a cleavable diazo group that releases nitrogen and 2-methoxyethanol, a volatile compound, to alter the P3HT film morphology. OECTs based on the film exhibit improved response times. Interestingly, the process also enhances the crystallinity of P3HT, leading to higher hole mobility compared with pristine P3HT. This study proposes an in situ strategy to achieve the functionality of the OMIEC via morphological regulation, offering a promising route to simultaneously enhance both ion accessibility and charge mobility.

Organic polymers↗
DOE OSTI2020

Electrostatic Barriers to Nanoparticle Accessibility of a Porous Matrix

Translocation from one cavity to another through a narrow constriction (i.e., a “hole”) represents the fundamental elementary process underlying hindered mass transport of nanoparticles and macromolecules within many natural and synthetic porous materials, including intracellular environments. This process is complex and may be influenced by long-range (e.g., electrostatic) particle–wall interactions, transient adsorption/desorption, surface diffusion, and hydrodynamic effects. In this study, we used a three-dimensional (3D) tracking method to explicitly visualize the process of nanoparticle diffusion within periodic porous nanostructures, where electrostatic interactions were mediated via ionic strength. The effects of electrostatic interactions on nanoparticle transport were surprisingly large. For example, an increase in the Debye length of only a few nanometers (in a material with a hole diameter of ~100 nm) increased the mean cavity escape time 3-fold. A combination of computational and experimental analyses indicated that this hindered cavity escape was due to an electrostatic energy barrier in the region of the hole, which was quantitatively explained using DLVO theory. These findings explicitly demonstrate that the cavity escape process was barrier-limited and dominated by electrostatic effects.

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

Coarse-grained molecular dynamics simulation of solvent-dependent cellulose nanofiber interactions

Associations between cellulose are important both in biofuel production and in the use of cellulose for biomaterials. Cellulose nanofibers (CNFs) are sustainable, strong, light-weight alternatives to traditional materials in manufacturing, but are challenging to obtain due to irreversible aggregation in solution during preparative fibrillation. Therefore, it is imperative to understand the underlying factors driving aggregation with a view to designing solvents that can effectively compete with interfiber interactions, hence reducing aggregation. Molecular dynamics (MD) simulation at atomic detail can provide useful information on local interactions. However, the length and timescales accessible are too short to fully capture association processes. Here, we provide a method for accessing the longer length and timescales required using coarse-grained (CG) MD simulations with a MARTINI force field to calculate the interaction behavior of CNFs in three selected solvents: NaOH-urea-water, acetone, and neat water. The CG results are consistent with our prior all-atom MD and with previous experimental results. While acetone is found not to be an effective solvent, urea and ionic moieties in NaOH-urea-water not only solvate the fibrils but also improve the confinement of water molecules around them as shown by the solvent residence times and mean-square displacements. Overall, the presence of urea and ions reduces the likelihood of aggregation in multi-CNF systems relative to neat water irrespective of whether the hydrophobic or hydrophilic CNF surfaces are interacting. In conclusion, the CG method shows clear promise for selecting potential high-performance solvents for experimental prioritization in bioenergy and biomaterials research in a relatively fast manner as well as for understanding the aggregation and rheological behavior of CNF-solvent systems.

aggregation↗
DOE OSTI2024

Probing the potential of type V Deep eutectic solvents as sustainable electrolytes

The increasing interest within the scientific community in environmentally friendly solvents has led to a focus on Deep Eutectic Solvents (DES), which have natural components. DES are viewed as alternatives to traditional organic solvents and have the potential to be used as electrolytes. For the first time, transport properties of four Type V Deep Eutectic Salt Solutions (DESS) were accessed to investigate the potential of this technology, selecting precursors ranked as excellent in Eco-Scale metrics. The DESS were composed of terpene and trioctylphosphine oxide (TOPO), and varying concentrations of lithium bis(trifluoromethane)sulfonimide (LiTFSI), and their properties were assessed through self-diffusion, viscosity, density, and conductivity measurements. While Type V DESS are capable of dissolving significant amounts of LiTFSI (up to 30 % molar), their ionic conductivity is low, with values ranging from 3.6·10 –3 to 9.3·10 –2 mS·cm –1 at 25 °C, thus limiting their suitability as electrolytes, for instance, for lithium-ions batteries applications. Similar diffusion coefficients for Li + and TFSI – ions suggest the formation of long-lived ion pairs moving as a neutral species. As a result, future research aims to introduce additives to disrupt contact ion pairs and enhance transport properties, leveraging the sustainable appeal of DES and their use in advanced energy storage technologies.

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

2024 roadmap on magnetic microscopy techniques and their applications in materials science

Considering the growing interest in magnetic materials for unconventional computing, data storage, and sensor applications, there is active research not only on material synthesis but also characterisation of their properties. In addition to structural and integral magnetic characterisations, imaging of magnetisation patterns, current distributions and magnetic fields at nano- and microscale is of major importance to understand the material responses and qualify them for specific applications. In this roadmap, we aim to cover a broad portfolio of techniques to perform nano- and microscale magnetic imaging using superconducting quantum interference devices, spin centre and Hall effect magnetometries, scanning probe microscopies, x-ray- and electron-based methods as well as magnetooptics and nanoscale magnetic resonance imaging. The roadmap is aimed as a single access point of information for experts in the field as well as the young generation of students outlining prospects of the development of magnetic imaging technologies for the upcoming decade with a focus on physics, materials science, and chemistry of planar, three-dimensional and geometrically curved objects of different material classes including two-dimensional materials, complex oxides, semi-metals, multiferroics, skyrmions, antiferromagnets, frustrated magnets, magnetic molecules/nanoparticles, ionic conductors, superconductors, spintronic and spinorbitronic materials.

2D materials↗
NASA NTRS1995

Results from the Heavy Ions In Space (HIIS) experiment on the ionic charge state of solar energetic particles

It has long been known that low-energy solar energetic particles (SEP's) are partially-ionized. For example, in large, so-called 'gradual' solar energetic particle events, at approximately 1 MeV/nucleon the measured mean ionic charge state, Q, of Fe ions is 14.1 +/- 0.2, corresponding to a plasma temperature of approximately 2 MK in the coronal or solar-wind source material. Recent studies, which have greatly clarified the origin of solar energetic particles and their relation to solar flares, suggest that ions in these SEP events are accelerated not at a flare site, but by shocks propagating through relatively low-density regions in the interplanetary medium. As a result, the partially-ionized states observed at low energies are expected to continue to higher energies. However, up to now there have been no high-energy measurements of ionic charge states to confirm this notion. We report here HIIS observations of Fe-group ions at 50-600 MeV/nucleon, at energies and fluences which cannot be explained by fully-ionized galactic cosmic rays, even in the presence of severe geomagnetic cutoff suppression. Above approximately 200 MeV/nucleon, all features of our data -- fluence, energy spectrum, elemental composition, and arrival directions -- can be explained by the large SEP events of October 1989, provided that the mean ionic charge state at these high energies is comparable to the measured value at approximately 1 MeV/nucleon. By comparing the HIIS observations with measurements in interplanetary space in October 1989, we determine the mean ionic charge state of SEP Fe ions at approximately 200-600 MeV/nucleon to be Q = 13.4 plus or minus 1.0, in good agreement with the observed value at approximately 1 MeV/nucleon. The source of the ions below approximately 200 MeV/nucleon is not yet clear. Partially-ionized ions are less effectively deflected by the Earth's magnetic field than fully-ionized cosmic rays and therefore have greatly enhanced access to low-Earth orbit. Moreover, at the high energies observed in HIIS, these ions can penetrate typical amounts of shielding. We discuss the significance of the HIIS results for estimates of the radiation hazard posed by large SEP events to satellites in low-Earth orbit, including the proposed Space Station orbit. Finally, we comment on previous reports of low-energy below-cutoff Fe-group ions, which some authors have interpreted as evidence for partially-ionized galactic cosmic rays. The LDEF flux levels are much smaller than the corresponding fluxes in these previous reports, implying that the source of these ions has an unusual solar-cycle variation and/or strongly increases with decreasing altitude.

Tylka, Allan J.↗
DOE OSTI2024

Local ionic transport enables selective PGM-free bipolar membrane electrode assembly

Bipolar membranes in electrochemical CO 2 conversion cells enable different reaction environments in the CO 2 -reduction and O 2 -evolution compartments. Under ideal conditions, water-splitting in the bipolar membrane allows for platinum-group-metal-free anode materials and high CO 2 utilizations. In practice, however, even minor unwanted ion crossover limits stability to short time periods. Here we report the vital role of managing ionic species to improve CO 2 conversion efficiency while preventing acidification of the anodic compartment. Through transport modelling, we identify that an anion-exchange ionomer in the catalyst layer improves local bicarbonate availability and increasing the proton transference number in the bipolar membranes increases CO 2 regeneration and limits K + concentration in the cathode region. Through experiments, we show that a uniform local distribution of bicarbonate ions increases the accessibility of reverted CO 2 to the catalyst surface, improving Faradaic efficiency and limiting current densities by twofold. Using these insights, we demonstrate a fully platinum-group-metal-free bipolar membrane electrode assembly CO 2 conversion system exhibiting <1% CO 2 /cation crossover rates and 80-90% CO 2 -to-CO utilization efficiency over 150 h operation at 100 mA cm -2 without anolyte replenishment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Polarons and electrical leakage in BaZrO 3 and BaCeO 3

The proton conductors barium zirconate (BaZrO 3 , or BZO), barium cerate (BaCeO 3 , or BCO), and their alloys have attracted considerable interest as solid-state electrolytes in solid-oxide fuel and electrolysis cells. However, the reasons for their non-negligible electrical conductivity, which can limit their performance, are not fully understood. To address that question, we use first-principles calculations based on density functional theory to study the properties of hole and electron polarons in BZO and BCO. We confirm that hole polarons form in both materials, slightly more favorably in BCO. Electron polarons, on the other hand, are stable only in BCO and in Ce-containing alloys; in pure BZO, electron polaron states are unfavorable relative to free carriers, though they become accessible when Ce impurities are introduced. In general, doped BZO and BCO will have negligible electron concentrations, but larger concentrations of holes and hole polarons may be present. Avoiding extreme O-rich conditions and limiting dopant concentrations are key strategies for reducing significant p -type electrical leakage. Furthermore, our results provide physical insights into the different electronic behaviors of BZO and BCO, which can be used to optimize their performance as pure ionic conductors.

08 HYDROGEN↗
DOE OSTI2021

Substrate Partitioning into Protein Macromolecular Frameworks for Enhanced Catalytic Turnover

Spatial partitioning of chemical processes is an important attribute of many biological systems, the effect of which is reflected in the high efficiency of enzymes found within otherwise chaotic cellular environments. Barriers, often provided through the formation of compartments or phase segregation, gate the access of macromolecules and small molecules within the cell and provide an added level of metabolic control. Taking inspiration from nature, we have designed virus-like particles (VLPs) as nanoreactor compartments that sequester enzyme catalysts and have used these as building blocks to construct 3D protein macromolecular framework (PMF) materials, which are structurally characterized using small-angle X-ray scattering (SAXS). Additionally, the highly charged PMFs form a separate phase in suspension, and by tuning the ionic strength, we show positively charged molecules preferentially partition into the PMF, while negatively charged molecules are excluded. This molecular partitioning was exploited to tune the catalytic activity of enzymes enclosed within the individual particles in the PMF, the results of which showed that positively charged substrates had turnover rates that were 8500× faster than their negatively charged counterparts. Moreover, the catalytic PMF led to cooperative behavior resulting in charge dependent trends opposite to those observed with individual P22 nanoreactor particles.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Recent advances in biomass pretreatment using biphasic solvent systems

The complexity and recalcitrance of lignocellulosic biomass seriously hinder its subsequent conversion to liquid fuels. To achieve high-value utilization of lignocellulosic biomass, the physical–chemical barrier should be overcome through appropriate pretreatment techniques to improve the accessibility of cellulose for efficient enzymatic hydrolysis. With the rapid emergence of novel pretreatment solvents, biphasic solvent pretreatments represent a nascent and green pretreatment method that has shown outstanding advantages and broad application prospects in the biorefinery of lignocellulosic substrates due to its ability to provide economically viable biomass upgrading, the separation process for products in the solvent phase, and the reutilization of solvents. Herein, different types of biphasic solvents (e.g., 2-methyltetrahydrofuran, methyl isobutyl ketone, 1-butanol, phenoxyethanol, ionic liquids, and deep eutectic solvents) were reviewed systematically, including the fundamental designs of biphasic solvents for biomass pretreatment, their effect on the fractionation of individual biomass components (e.g., carbohydrate and lignin) and the enzymatic hydrolysis performance, and the coproduction of furan and hydroxymethylfurfural. Finally, the main pros and cons of these different biphasic solvent systems are summarized, and the future development direction is also proposed. Finally, this review can provide a reference for designing and selecting effective biphasic pretreatment methods for various types of lignocellulosic biomass.

09 BIOMASS FUELS↗
DOE OSTI2025

Synthetic Accessibility and Sodium Ion Conductivity of the Na8–x A x P2O9 (NAP) High-Temperature Sodium Superionic Conductor Framework

Advancement of solid-state electrolytes (SSEs) for all solid-state batteries typically focuses on modification of a known structural framework to improve conductivity, e.g., cation substitution for an immobile ion or varying the concentration of the mobile ions. Novel frameworks can be disruptive by enabling fast ion conduction aided by different structure and diffusion mechanisms, thereby unlocking optimal conductors with different properties. Herein, we perform a high-throughput survey of a structural framework for sodium ion conduction, Na8–x A x P2O9 (NAP), to understand the family’s thermodynamic stability, synthesizability, and ionic conduction. We show that the parent phase Na4TiP2O9 (NTP) undergoes a structural distortion (with accompanying conductivity transition) due to unstable phonons arising from pseudo-Jahn–Teller mode in the 1D titanium chains. Screening compounds in which Ti is substituted by other metals computationally reveal a number of candidates that are predicted to be low in formation energy and have high predicted ionic conductivities. High-throughput experimental and subsequent methodology optimization trials deliver one new compound, Na4SnP2O9 (NSP). X-ray diffraction (XRD), microscopy, and spectroscopy characterization indicate that the room-temperature structure of NSP is similar to the high-temperature, orthorhombic NTP phase but with some small unresolved structural differences. These uncharacterized structural details are speculated to limit the ion conductivity. Temperature-dependent XRD and electrochemical impedance spectroscopy indicate multiple coupled conductivity–structure transitions at a high temperature. We demonstrate the challenges with synthesis development and a priori identification of promising SSE phases as a major bottleneck in new (energy) materials development.

Chemical reactions↗
DOE OSTI2020

Ions Tune Interfacial Water Structure and Modulate Hydrophobic Interactions at Silica Surfaces

The structure and ultrafast dynamics of the electric double layer (EDL) are central to chemical reactivity and physical properties at solid/aqueous interfaces. While the Gouy–Chapman–Stern model is widely used to describe EDLs, it is solely based on the macroscopic electrostatic attraction of electrolytes for the charged surfaces. Structure and dynamics in the Stern layer are, however, more complex because of competing effects due to the localized surface charge distribution, surface–solvent–ion correlations, and the interfacial hydrogen bonding environment. Here, we report combined time-resolved vibrational sum frequency generation (TR-vSFG) spectroscopy with ab initio DFT-based molecular dynamics simulations (AIMD/DFT-MD) to get direct access to the molecular-level understanding of how ions change the structure and dynamics of the EDL. We show that innersphere adsorbed ions tune the hydrophobicity of the silica–aqueous interface by shifting the structural makeup in the Stern layer from dominant water–surface interactions to water–water interactions. This drives an initially inhomogeneous interfacial water coordination landscape observed at the neat interface toward a homogeneous, highly interconnected in-plane 2D hydrogen bonding (2D-HB) network at the ionic interface, reminiscent of the canonical, hydrophobic air–water interface. This ion-induced transformation results in a characteristic decrease of the vibrational lifetime (T 1 ) of excited interfacial O–H stretching modes from T 1 ~ 600 fs to T 1 ~ 250 fs. Hence, we propose that the T 1 determined by TR-vSFG in combination with DFT-MD simulations can be widely used for a quantitative spectroscopic probe of the ion kosmotropic/chaotropic effect at aqueous interfaces as well as of the ion-induced surface hydrophobicity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Passivation‐Induced Species Dynamics and Microstructural Evolution in Solid‐State Lithium–Sulfur Cathodes

Solid-state lithium–sulfur (SSLS) batteries offer high theoretical energy density, yet their practical viability is hindered by poor sulfur utilization and limited rechargeability. At the core of this challenge lies the passivating nature of Li 2 S, which restricts ionic and electronic transport, suppresses interfacial activity, and severely impedes the reversibility of electrochemical reactions. In this study, we elucidate the mechanistic origins of these limitations by resolving how charge and discharge species form, grow, and spatially evolve within the cathode microstructure under varied current densities and electrode compositions. By resolving the species distribution at the particle scale and coupling it with Raman spectroscopy and X-ray diffraction, we demonstrate how Li 2 S formation induces localized surface passivation that progressively limits electrochemical accessibility within the cathode microstructure. Sulfur utilization is found to be strongly governed by the interplay between sulfur loading, residual porosity, and interfacial architecture. High sulfur contents result in buried, electrochemically isolated domains due to poor solid electrolyte (SE) percolation, while low sulfur contents trigger SE degradation via parasitic reactions. The resulting sulfur-porosity maps delineate the mechanistic boundaries between reversible and transport-limited regimes, offering actionable design guidance for SSLS cathodes with enhanced sulfur utilization.

electrode microstructure↗
DOE OSTI2023

Raman Wavelength Conversion in Ionic Liquids

Here, we explore the use of room-temperature ionic liquids (ILs) as Raman wavelength converters. ILs provide an engineerable framework to design suitable liquids for wavelength conversion over a broad spectral range, through careful selection of the molecular structures of the IL anions and cations so that specific characteristics can be obtained, such as a desirable Raman shift, low Brillouin scattering, and good optical transmission in the pump and Stokes wavelengths. Applying such criteria, we demonstrate that 1-ethyl-3-methylimidazolium dicyanamide (EMIM DCA) is an effective medium for conversion of 532-nm pulses from a Q-switched Nd :YAG laser to 603 nm. This corresponds to an approximate 2200 cm –1 shift, which can be used to generate mid-infrared radiation through subsequent difference frequency generation for optical pumping of CO 2 lasers. Threefold-higher Raman conversion efficiency is obtained in EMIM DCA compared with water under identical conditions in a proof-of-principle single-pass conversion setup, resulting in an efficient generation of multimillijoule, <6 ns duration, high-quality orange laser pulses in a wavelength region that is difficult to access at high energies. Consequently, we examine ILs representing two other classes of Raman-active functional groups and obtain conversion up to the fifth-order Stokes shift and first anti-Stokes shift. Through the tunable selection of their components and their useful dynamical properties, ILs provide a platform for efficient, simple, and alignment-tolerant high-energy Raman shifting with numerous industrial and technological applications.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2025

Cation Crossover Limits Accessible Current Densities for Zero-Gap Alkaline CO2 Reduction to Ethylene

Traditional CO2 reduction systems often fail in an alkaline environment due to the interaction of CO2 with a high-pH electrolyte, where carbonate and bicarbonate ion formation results in potassium-containing salt precipitation. The presence of the salt crystals causes a reduction in the selectivity of the electrolyzer toward CO2 conversion. Here, the critical operational variables, which elicit the salting out process, are investigated (i.e., ion transport). When the electrolyzer exceeds a critical current density, H2 evolution dominates CO2 reduction due to salt formation, which is confirmed by postmortem cross-sectional SEM-EDS of the electrode. The critical current density decreases with an increasing membrane thickness or anolyte ionic strength. Cathode salt formation is mediated by the unmitigated crossover of cations from the anolyte to the cathode across an anion exchange membrane, through which cations are imperfectly excluded. It is likely that electric field-driven migration promotes an increase in concentration of potassium across the membrane, until, at the critical current density for that electrolyzer arrangement, the concentration of potassium and bicarbonate ions exceeds the solubility limit of KHCO3, leading to salt precipitation.

CO2 reduction↗