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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Anion exchange membranes based on (3-acrylamidopropyl) trimethylammonium chloride (APTA) and phenyl Acrylate: Impact of crosslinker and crosslinker content on physiochemical properties and transport behavior of acetate and formate

CO 2 reduction cells are innovative devices that convert CO 2 into valuable chemicals, such as formate (OFm - ) and acetate (OAc - ), at the cathode. One of the key challenges in these devices is the development of ion exchange membranes that enable the transport of charge carriers between electrodes while minimizing the transfer of CO 2 reduction products. This study focuses on the preparation and characterization of crosslinked anion exchange membranes (AEMs) made of phenyl acrylate (PA) and (3-acrylamidopropyl) trimethylammonium chloride (APTA), crosslinked with either poly(ethylene glycol) diacrylate (PEGDA) or N,N’-methylenebisacrylamide (MBAA). Here, the membranes are characterized to understand their physiochemical properties and corresponding transport behavior through characterization of water volume fraction, mechanical properties, ionic conductivity, ion exchange capacity, water contact angle, glass transition temperature as well as their permeability and solubility to formate and acetate. MBAA crosslinked membranes exhibit higher Young’s modulus and lower strain at break compared to PEGDA-crosslinked membranes, which is attributed to their shorter chain length. Within a series of membranes of varied comonomer content, for either PEGDA or MBAA as crosslinker, permeabilities generally follow free volume theory (increasing permeability with increasing water content where water content increases with decreasing crosslinker content). Interestingly, for membranes with different crosslinkers but analogous water volume fraction significant differences (∼2 orders of magnitude) in permeability are observed which we attribute to differences in chain mobility as characterized through the glass transition temperature.

25 ENERGY STORAGE↗
DOE OSTI2025

Understanding the impact of SPMAK and PEGPEA in crosslinked PEGDA membranes: Methanol-carboxylate co-transport behavior and correlating structure-physicochemical-transport properties

Investigating multicomponent transport in dense, hydrated polymer membranes is necessary in applications such as fuel cells, electrolyzers, and desalination systems. Of particular interest are photoelectrochemical CO 2 reduction cells (PEC-CRC) which produce liquid products such as alcohols (methanol) and carboxylates (formate, acetate). Flux coupling and competitive sorption behavior of these products (solutes) have been found to affect permselectivity, thereby motivating us to investigate fundamental membrane structure-physicochemical-transport relationships. Past research has shown that systematic tuning of crosslinked cation exchange membranes (CEMs) with charge-neutral monoacrylate monomers containing alkyl and phenyl groups (i.e., poly(ethylene glycol) methacrylate (PEGMA), and poly(ethylene glycol) phenyl ether acrylate (PEGPEA)) can suppress acetate transport (permeability) in co-permeation with methanol. To further investigate this transport behavior and to enhance membrane ionic conductivities, 3-sulfopropyl methacrylate potassium (SPMAK), a sulfonated monoacrylate monomer is incorporated here. SPMAK content is varied with neutral PEGPEA and diacrylate crosslinker, poly (ethylene glycol) diacrylate (PEGDA) of two different chain lengths (n = 10 and 13) to prepare membranes of various compositions. Electrochemical and physicochemical properties including ionic conductivity, ion exchange capacity, and water uptake increase with increasing charged SPMAK content. Different states of water within hydrated membranes are probed using differential scanning calorimetry (DSC), where increasing intermediate (loosely bound) water is observed with increasing hydrophilic SPMAK content. The transport behavior of methanol and carboxylates (formate, acetate, propionate) are investigated, where permeabilities vary as methanol > formate > acetate ≈ propionate. Interestingly, permeabilities decrease with increasing PEGPEA content and are more dependent on solute diffusion than sorption. Permeabilities and diffusivities decrease while permselectivities increase with decreasing PEGDA chain length.

25 ENERGY STORAGE↗
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 OSTI2020

PbS/CdS Quantum Dot Room-Temperature Single-Emitter Spectroscopy Reaches the Telecom O and S Bands via an Engineered Stability

We synthesized PbS/CdS core/shell quantum dots (QDs) to have functional single-emitter properties for room-temperature, solid-state operation in the telecom O and S bands. Two shell-growth methods–cation exchange and successive ionic layer adsorption and reaction (SILAR)–were employed to prepare QD heterostructures with shells of 2–16 monolayers. PbS/CdS QDs were sufficiently bright and stable to resolve photoluminescence (PL) spectra representing both bands from single nanocrystals using standard detection methods, and for a QD emitting in the O-band a second-order correlation function showed strong photon antibunching, important steps toward demonstrating the utility of lead chalcogenide QDs as single-photon emitters (SPEs). Irrespective of type, few telecom-SPEs exist that are capable of such room-temperature operation. Access to single-QD spectra enabled a direct assessment of spectral line width, which was ~70–90 meV compared to much broader ensemble spectra (~300 meV). We show inhomogeneous broadening results from dispersity in PbS core sizes that increases dramatically with extended cation exchange. Quantum yields (QYs) are negatively impacted at thick shells (>6 monolayers) and, especially, by SILAR-growth conditions. Time-resolved PL measurements revealed that, with SILAR, initially single-exponential PL-decays transition to biexponential, with opening of nonradiative carrier-recombination channels. Radiative decay times are, overall, longer for core/shell QDs compared to PbS cores, which we demonstrate can be partially attributed to some core/shell sizes occupying a quasi-type II electron–hole localization regime. Finally, we demonstrate that shell engineering and the use of lower laser-excitation powers can afford significantly suppressed blinking and photobleaching. However, dependence on shell thickness comes at a cost of less-than-optimal brightness, with implications for both materials and experimental design

36 MATERIALS SCIENCE↗
DOE OSTI2022

Unconventional Highly Active and Stable Oxygen Reduction Catalysts Informed by Computational Design Strategies

As conventional strategies of engineering new MIEC materials for SOFCs over the past few decades would have eliminated a material like BFCZ75 from contention, this work suggests there is a need to re-think existing design criteria and develop and understand new rational materials design strategies that challenge conventional wisdom and chemical intuition. The ultimate goal of cathode design of SOFCs is to achieve a balance among electrical conductivity, ionic conductivity, oxygen exchange activity and long-term stability. Instead of searching for a replacement for unstable MIEC like LSCF, which works well in a ceria based composite electrode, some stable composites contain a highly conductive material mixing with a less conductive but highly ORR active and stable MIEC such as BFCZ75 or even triple-phase composites could be an alternative way to advance the current SOFC technology. (This work is published in May 2022 issue of Advanced Energy Materials. https://doi.org/10.1002/aenm.202201203 --&gt;)<br>

Liu, Jian↗
DOE OSTI2022

Metal–Organic Framework Integrating Ionic Framework and Bimetallic Coupling Effect for Highly Efficient Oxygen Evolution Reaction

Metal–organic frameworks (MOFs) are recognized as promising electrocatalysts for the oxygen evolution reaction (OER) because of their permanent porosity and rich architectural diversity; however, ionic MOFs enabling fast ions exchange during OER are rarely explored. Here, an ionic MOF (Ni-btz) constructed with an azolate ligand is selected, and continuous 3D bimetallic MOF (NiFe-btz) films deriving from high-degree intergrowth of microsized MOFs particles are fabricated. The as-prepared NiFe-btz/NF-OH electrode exhibits excellent OER performance with a low overpotential of 239 mV at 10 mA cm –2 under alkaline condition. The OER charge transfer process and bimetallic coupling effect in ionic NiFe-btz are probed by density functional theory calculations and confirmed via X-ray photoelectron spectroscopy and in situ Raman measurements. The partial density of states of NiFe-btz indicates that the main contribution for electron density around the Fermi level is from Cl ions clarifying the profitable impact of ionic MOF framework. This work systematically demonstrates the relationship of electronic structure and OER activity in ionic, bimetallic MOFs and expands the scope of 3D MOF films for efficient OER.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Non-classical ion-indiffusion processes in quasi-one-dimensional ionic conductor KTiOPO4

Developments in coercive field engineering and waveguide writing via ion-exchange in the ferroelectric ionic-conductor KTiOPO4 (KTP) have led to breakthroughs within the field of nonlinear optics and quantum photonics. However, the microscopic diffusion dynamics of ion-exchange in KTP are poorly understood and show signs of non-classical diffusion dynamics. The precise control of ion-exchange gradients is critical for developing KTP into a mature, integrated nonlinear optical material but requires a level of control that, in turn, demands a deeper understanding of the ion-exchange process. We employ direct ToF-SIMS mapping to untangle the complex diffusion dynamics of the commonly used ion-exchange dopant ions: Rb, Ba, and K. We map periodic diffusion gradients of two exchanges, one dominated by Rb-ions and the other by Ba-ions. For the first time, we show the interdependent nature of the Ba- and Rb ion in the ion-exchange diffusion gradient. The low incorporation of the Ba ion is mapped and quantified, and dopant–crystal interactions are identified. This work highlights the complex diffusion dynamics of dopants in the KTP structure and lays the foundation for deterministic control of diffusion gradients for the next generation of integrated nonlinear and quantum photonic devices.

Barrett, Laura [ORNL]↗
DOE OSTI2021

Sodium, Silver and Lithium-Ion Conducting β''-Alumina + YSZ Composites, Ionic Conductivity and Stability

Na-β''-alumina (Na 2 O.~6Al 2 O 3 ) is known to be an excellent sodium ion conductor in battery and sensor applications. In this study we report fabrication of Na- β''-alumina + YSZ dual phase composite to mitigate moisture and CO 2 corrosion that otherwise can lead to degradation in pure Na-β''-alumina conductor. Subsequently, we heat-treated the samples in molten AgNO 3 and LiNO3 to respectively form Ag-β''-alumina + YSZ and Li-β''-alumina + YSZ to investigate their potential applications in silver- and lithium-ion solid state batteries. Ion exchange fronts were captured via SEM and EDS techniques. Their ionic conductivities were measured using electrochemical impedance spectroscopy. Both ion exchange rates and ionic conductivities of these composite ionic conductors were firstly reported here and measured as a function of ion exchange time and temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Accurately measuring the ionic conductivity of membranes via the direct contact method

Accurately measuring the ionic conductivity of membranes is important both for assessing the performance of new membranes as well as for advancing the fundamental understanding of electric field-driven ion transport in membranes. Yet, despite a considerable number of reports on the topic, there is no standardized method for ionic conductivity measurements. One of the main challenges with ionic conductivity measurements is isolating the membrane resistance from the other resistances in the electrochemical cell. In this study, we present a detailed discussion of factors that affect ionic conductivity measurements with the commonly used direct contact method, in which the membrane contacts the electrodes. Such factors include external resistances due to imperfect contact between the membrane and electrodes, residual impedances due to the sample holder and wiring, and fringe effects. Further, we also present and validate simple methods for isolating the true membrane ionic conductivity in both the through-plane and in-plane orientations. These methods can be implemented with virtually any membrane to obtain accurate and reproducible ionic conductivity values. Finally, we outline recommendations for performing ionic conductivity measurements with the direct contact method and a set of parameters to verify when reporting these results.

36 MATERIALS SCIENCE↗
DOE OSTI2024

How hydrophobicity, side chains, and salt affect the dimensions of disordered proteins

Abstract Despite the generally accepted role of the hydrophobic effect as the driving force for folding, many intrinsically disordered proteins (IDPs), including those with hydrophobic content typical of foldable proteins, behave nearly as self‐avoiding random walks (SARWs) under physiological conditions. Here, we tested how temperature and ionic conditions influence the dimensions of the N‐terminal domain of pertactin (PNt), an IDP with an amino acid composition typical of folded proteins. While PNt contracts somewhat with temperature, it nevertheless remains expanded over 10–58°C, with a Flory exponent, ν , >0.50. Both low and high ionic strength also produce contraction in PNt, but this contraction is mitigated by reducing charge segregation. With 46% glycine and low hydrophobicity, the reduced form of snow flea anti‐freeze protein (red‐sfAFP) is unaffected by temperature and ionic strength and persists as a near‐SARW, ν ~ 0.54, arguing that the thermal contraction of PNt is due to stronger interactions between hydrophobic side chains. Additionally, red‐sfAFP is a proxy for the polypeptide backbone, which has been thought to collapse in water. Increasing the glycine segregation in red‐sfAFP had minimal effect on ν . Water remained a good solvent even with 21 consecutive glycine residues ( ν > 0.5), and red‐sfAFP variants lacked stable backbone hydrogen bonds according to hydrogen exchange. Similarly, changing glycine segregation has little impact on ν in other glycine‐rich proteins. These findings underscore the generality that many disordered states can be expanded and unstructured, and that the hydrophobic effect alone is insufficient to drive significant chain collapse for typical protein sequences.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Morphology and Transport of Multivalent Cation-Exchanged Ionomer Membranes Using Perfluorosulfonic Acid–Ce Z+ as a Model System

Perfluorosulfonic acids (PFSAs) are commonly used as solid polymer electrolyte membranes (PEMs) in electrochemical energy devices, where they are vulnerable to attack by radical species during operation. A popular strategy to combat this problem is to introduce radical scavengers like cerium (Ce) ions that neutralize these species before they attack the PFSA. Such cation doping creates a multi-ion system, in which understanding the mechanisms of cation solvation and transport becomes important for the effective design and utilization of PFSA–cation systems. Ce ions also provide a representative model system for multication-exchanged ionomers in electrochemical systems. In this study, hydration and conductivity measurements, along with X-ray fluorescence and scattering, are employed to elucidate how Ce ion exchange alters PFSA’s ionic solvation, as well as nano- and mesoscale morphologies, which ultimately control its ion transport properties. A molecular transport model is used to deconvolute the impact of Ce ions on the local solvation structure of water in the membrane from mesoscale changes of the transport pathways. The combined experimental and theoretical analysis reveals a nonlinear decrease in conductivity driven by cation solvation at the molecular level and morphological changes at longer length scales. Migration–diffusion coupling, its nonlinear dependence on ion exchange and hydration, and its overall implications for ionomer performance are also discussed. Finally, these findings have the potential to be translated into other mixed cation–ionomer systems for a wide range of energy and environmental devices.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Salt and ion transport in a series of crosslinked AMPS/PEGDA hydrogel membranes

Salt permeability and ionic conductivity are critical properties for membranes in water purification and energy applications. Both properties depend on individual ion sorption and diffusion coefficients, which are significantly influenced by polymer chemical and physical parameters such as fixed charge concentration and membrane water content. However, systematic studies connecting polymer structure to ion transport properties are still lacking. In this study, a series of uncharged and charged membranes were synthesized using poly(ethylene glycol) diacrylate (PEGDA) as a cross-linker and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) as a charged monomer. Membrane fixed charge concentration and water uptake were systematically varied by adjusting AMPS content in the pre-polymerization mixture. Salt sorption and permeability coefficients and ionic conductivity of these membranes were measured as a function of NaCl solution concentration (0.01–1 M). Combining the solution-diffusion model and Nernst-Planck equation, individual ion diffusion coefficients were calculated. Experimental Na + diffusion coefficients for all materials were well described by the Mackie and Meares tortuosity model, highlighting the strong influence of water content on ion diffusivity in both uncharged and charged polymers. Model predictions for Cl – diffusion coefficients agree reasonably well with experimental values, with some deviations occurring in more highly charged membranes. Finally, this discrepancy might result from interactions not captured by the Mackie and Meares model (e.g., fixed charge-ion interactions).

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

Processing iridium foil targets for the production of radioplatinum isotopes

Dissolving noble metals remains challenging because of their high reduction potentials and tendency to passivate as oxides. This barrier is acute for iridium metal targets used to produce platinum radioisotopes, where post-irradiation processing is costly and hazardous with conventional routes. Here, we report a rapid alkali-fusion method that converts Ir metal directly into chloride media compatible with downstream separations. In the process, an Ir foil is fused with Na 2 O 2 and KCl at temperatures above the KCl melting point; the molten salt enhances heat transfer and facilitates O 2− /Na + transport to the Ir surface, overcoming Ir's oxidation resistance. The fused cake is then cooled and leached in 10 M HCl, yielding Ir in solution without specialized microwave digestion or HF. Pt separation from bulk Ir was evaluated using extraction-chromatography resins. A newly formulated ionic-liquid resin containing Cyphos IL 104 (E104) was compared with two commercial resins (TrisKem TK200 and TK201). All resins achieved >90 % Ir recovery. Pt co-recovery depended on resin chemistry: TK200 recovered 85.9 % Pt, TK201 recovered 54.1 % Pt, and E104 recovered 72.9 % Pt. This study introduces a fast, scalable dissolution route for solid Ir targets and demonstrates resin choices that tune Ir/Pt separation, lowering the barrier to routine production and purification of Pt radioisotopes.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2021

Migration Kinetics of Surface Ions in Oxygen-Deficient Perovskite During Topotactic Transitions

Oxygen diffusivity and surface exchange kinetics underpin the ionic, electronic, and catalytic functionalities of complex multivalent oxides. Towards understanding and controlling the kinetics of oxygen transport in emerging technologies, it is highly desirable to reveal the underlying lattice dynamics and ionic activities related to oxygen variation. In this study, the evolution of oxygen content is identified in real-time during the progress of a topotactic phase transition in La 0.7 Sr 0.3 MnO 3-δ epitaxial thin films, both at the surface and throughout the bulk. Using polarized neutron reflectometry, a quantitative depth profile of the oxygen content gradient is achieved, which, alongside atomic-resolution scanning transmission electron microscopy, uniquely reveals the formation of a novel structural phase near the surface. Surface-sensitive X-ray spectroscopies further confirm a significant change of the electronic structure accompanying the transition. The anisotropic features of this novel phase enable a distinct oxygen diffusion pathway in contrast to conventional observation of oxygen motion at moderate temperatures. The results provide insights furthering the design of solid oxygen ion conductors within the framework of topotactic phase transitions.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Numerical study of the chemo-mechanical behavior of FEBEX bentonite in nuclear waste disposal based on the Barcelona expansive model

Experimental studies show that compacted bentonite used as a backfill material for nuclear waste repository experiences strong coupling between chemical and mechanical processes. Here, we use a dual-structure expansive soil model, referred to as the Barcelona Expansive Model (BExM), to predict the behavior of bentonite buffer in subsurface emplacement tunnels for high-level radioactive waste. After emplacement, the bentonite is subjected to complex and coupled Thermal-Hydraulic-Mechanical-Chemical (THMC) processes. The BExM constitutive model is implemented in a multi-phase reactive transport and geomechanics simulator, TOUGHREACT-FLAC3D, and the model is verified with one benchmark test on FEBEX bentonite. We utilize a one-way Chemo-Mechanical (C-M) coupling approach, in which chemical changes affect the mechanical behavior of bentonite through the BExM linked with the evolution of mass fraction of smectite, exchangeable cation concentration, and ionic strength via osmotic suction. The parameters of the new coupled model for FEBEX bentonite are calibrated against a series of laboratory experiments with various salinity solutions. Finally, coupled THMC modeling is conducted for a generic argillite repository with bentonite buffer under high temperature, focusing on the long-term chemical change and its effect on the mechanical process.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2025

Understanding and controlling the fundamental photochemistry of protonic solar energy conversion (Final Scientific/Technical Report)

The selectivity and activity of most fuel-forming reactions are tunable by the concentration of electrons, holes, protons, and/or hydroxides. That is one reason why traditional solar energy conversion processes are used to drive these reactions, where light directly increases the concentration of electrons and holes. We, instead, took a different approach, using light to increase the concentration of protons and/or hydroxides. For this, we leveraged photophysical and solid-state physics theories, techniques, and design strategies previously developed for the study of traditional solar energy conversion processes. We designed and fabricated several materials platforms based on molecular photoacid and photobase dyes coupled with ion-exchange polymer membranes and assessed their fundamental photoelectrochemistry. We demonstrated control over built-in electric potentials, photovoltages, proton-transfer kinetics, and efficiency limits to our approach. Understanding the basic science of these dye-sensitized protonic membranes and their photochemical mechanisms is of use to the DOE-relevant processes of solar photochemical fuel formation, solar photodialytic desalination, and solar cells. Moreover, functional materials that we developed from this project may be of use to several broad-reaching fields and may provide the foundation for a completely new, inexpensive, and robust solar energy conversion technology.

14 SOLAR ENERGY↗
DOE OSTI2023

Surface oxygen exchange kinetics of mixed conducting oxides: Dilatometric vs electrical conductivity relaxation study

The surface oxygen exchange kinetics of mixed ionic-electronic conducting (MIEC) oxides play a crucial role in a variety of applications, including solid oxide fuel/electrolysis cells (SOFCs/SOECs), permeation membranes and sensors. To date, a variety of methods, including isotope exchange, electrical conductivity, optical absorptivity and thermogravimetry relaxation, and impedance spectroscopy have been used to measure the oxygen exchange coefficient of MIEC oxides. Each of these methods have their advantages and limitations, depending on the physical and chemical properties of the investigated materials and their sample dimensions and densities. Here, we demonstrate the ability to precisely measure the surface oxygen exchange coefficient (k chem ) of MIEC model material Pr 0.1 Ce 0.9 O 2-δ (PCO) by use of dilatometric relaxation measurements, particularly of interest for materials that exhibit larger chemical expansion coefficients. This is achieved by use of porous bulk specimens to ensure that the contribution of oxygen exchange to the overall kinetics is dominant. We demonstrate that k chem values extracted from chemical expansion relaxation measurements on PCO are nearly identical to those derived from electrical conductivity relaxation measurements. As a result, this provides the opportunity to precisely investigate the oxygen exchange and chemical expansion kinetics of a wide range of materials used in high-temperature applications, particularly where more conventional methods are difficult or inappropriate to apply.

(Pr,Ce)O2-x↗
DOE OSTI2023

LTE-P-22 Alkaline Stability of AEMs

A procedure for ex-situ evaluation of chemical (alkaline) stability of anion exchange membranes (AEM). The IEC and ionic conductivity of an AEM is measured before and after being heated (typically at 80C in 1 M KOH) for ~1000 hours.

AEM↗