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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

An Educational Program on Concentrated Solar Power and Heliostats for Power Generation and Industrial Processes

The objective of this project was to design and implement a comprehensive educational and applied research program in Concentrated Solar Thermal Power (CSTP) and heliostat technologies at Northeastern University. In alignment with the U.S. Department of Energy's Heliostat Consortium (HelioCon) goals, the project aimed to expand student and public understanding of CSTP systems while simultaneously contributing to workforce development and the broader decarbonization strategy. A particular emphasis was placed on integrating hands-on student design projects and publicly disseminating educational content relevant to CSTP systems. The project addressed a critical gap in renewable energy education: CSTP and heliostats, despite their importance in utility-scale solar energy, are rarely included in standard mechanical engineering programs. This project established new pathways for students to engage with the topic through the creation of a 4-credit graduate/senior elective course, development of five industry-facing short courses, and the inclusion of CSTP-based capstone design projects. Over two academic years, 36 students across six senior design teams developed and tested technologies such as deformable heliostats, beacon-based tracking systems, and solar-powered pyrolizers for biomass-to-biochar conversion. Concurrently, 30 undergraduate and graduate students were enrolled in the new academic course centered around CSTP principles. To ensure the relevance and accessibility of the short course content, the project team engaged with industry professionals, technical policy stakeholders, and potential course participants through structured surveys and informal consultations. Feedback from 28 respondents guided the structure, length, and delivery format of the courses - resulting in a modular design broken into five workshops. The feedback emphasized the need for flexible, asynchronous delivery and practical case studies, particularly in areas such as heliostat control, thermal storage, and solar fuel production. This engagement helped align the courses with the evolving knowledge demands of the renewable energy workforce and ensured that participants from both technical and policy backgrounds could meaningfully benefit from the material. The research and educational activities advanced the understanding of heliostat control systems, optical performance under misalignment, and thermal system integration in solar-driven pyrolysis applications. Methods and designs explored in this project proved to be both technically effective and economically feasible at the lab scale. Prototypes were constructed using commercially available components and custom-fabricated elements, demonstrating that meaningful performance improvements can be achieved with modest material and fabrication costs, supporting the feasibility of student-led research in this field. The public benefit of this project is twofold. First, it cultivates a pipeline of engineers trained to be familiar with CSTP principles, an essential workforce need identified by the Department of Energy for achieving its 2030 cost and deployment targets. Second, it contributes openly accessible educational materials, course content, and experimental frameworks to the broader community, enabling other institutions to adopt or adapt similar programming. Through outreach activities, curriculum integration, and technical exposure, this project contributes to a more informed and capable renewable energy workforce while supporting innovation in heliostat and CSTP system design. A new technical report is being prepared to document the development of the course and its outcomes, with plans to publish it in the ASME Open Access Journal of Engineering to ensure global accessibility, free of cost.

14 SOLAR ENERGY↗
DOE OSTI2025

Physical properties of intergrowth compound Eu 2 CuZn 2 P 3

Here, the physical properties of single-crystalline Eu 2 ⁢CuZn 2 ⁢P 3 were inspected via thermodynamic, transport, and neutron diffraction measurements. Eu 2 ⁢ CuZn 2⁢ P 3 is composed of EuCuP and EuZn 2 ⁢ P 2 motifs stacked in a one-to-one ratio. The magnetic response of Eu 2 ⁢ CuZn 2 ⁢ P 3 is similar to that of EuZn 2 ⁢ P 2 in its A-type antiferromagnetic (semiconducting) state. A Néel temperature of T N = 40.3K is obtained from the specific heat capacity. Single-crystal neutron diffraction reveals a (001) magnetic propagation vector, with primarily in-plane moments coupled along [001] in an up-up-down-down pattern. This spin structure retains the ferromagnetic EuCuP motifs and antiferromagnetic coupling across the EuZn 2 ⁢P 2 motifs. The electrical resistivity is characterized by metallic behavior above 100 K, an increase in ρ upon cooling below ≈ 75K, and a large negative magnetoresistance below T N . First principles calculations evidence a narrow band gap for antiferromagnetic ordering and semimetallic behavior for the ferromagnetic state. This is consistent with the observed effect of magnetic field on the electrical resistivity. Hall effect measurements reveal a field-induced, negative anomalous Hall effect that increases on cooling down to 2 K. Also, an unconventional contribution to the Hall effect dominates the low-field Hall signal, particularly near T N , and is similar in appearance to a topological Hall effect. However, further work is necessary to understand if any of the transport properties have topological origins or if magnetism-induced modifications to the Fermi surface induce these unusual Hall effect signals in this and related materials.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Laser-induced forces on atoms during ultrafast demagnetization

Laser-induced femtosecond demagnetization has attracted a broad attention as a possible candidate for information storage technology. However, whether or not lattice vibration directly participates in demagnetization has been highly controversial over a decade. A recent electron diffraction experiment attributed the demagnetization to the polarized phonon effect, but a similar x-ray diffraction experiment attributed it to the Einstein–de Haas effect. Common to both experiments is that neither the angular momentum of the lattice nor the rotation of the sample was directly probed. Here, we report our first first-principles calculation of forces on atoms induced by an ultrafast laser during ultrafast demagnetization. We employ two complementary methods: (i) the frozen lattice with electronic excitation and (ii) frozen excitation but moving the lattice. We find that the forces on atoms start at –50 fs and peak around 30 fs. The magnitude of the force is far smaller than the empirical estimates. Within the limit of our theory, our results suggest that the polarized phonon effect and the Einstein–de Haas effect are unlikely to be the main course of demagnetization. As a result, we expect that our finding has a profound impact on the future direction of laser-induced dynamics in magnetic and quantum materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

An attempt to simulate laser-induced all-optical spin switching in a crystalline ferrimagnet

Interest in all-optical spin switching (AOS) is growing rapidly. The recent discovery of AOS in Mn 2 RuGa provides a much needed clean case of crystalline ferrimagnets for theoretical simulations. Here, we attempt to simulate it using the state-of-the-art first-principles method combined with the Heisenberg exchange model. We first compute the spin moments at two inequivalent manganese sites and then feed them into our model Hamiltonian. We employ an ultrafast laser pulse to switch the spins. We find that there is a similar optimal laser field amplitude to switch spins. However, we find that the exchange interaction has a significant effect on the system switchability. Weakening the exchange interaction could make the system unswitchable. This provides a crucial insight into the switching mechanism in ferrimagnets.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Advanced Ab Initio Methods for Nuclear Structure (Final Report)

Over the past decade, there has been enormous progress in the description of nuclear structure from first principles, using interactions from Chiral Effective Field Theory that are rooted in Quantum Chromodynamics, the fundamental theory of strong interactions, and many-body methods that solve the Schrödinger equation with systematically improvable approximations. Amongst those are the family of In-Medium Similarity Renormalization Group (IMSRG) framework developed by the PI and his co-workers. While these methods scale polynomially in the size N of the single-particle basis, computational efforts still grows dramatically as we increase the degrees of freedom for the nucleons by relaxing symmetries or introducing continuum couplings (see below), or as we push to improved truncations to provide precise inputs for experimental efforts, in particular in fundamental symmetry searches. In order to address this growing computational cost, one focus area of this award was the exploration of compression and factorization methods. The key to success or failure is the presence of low-rank structures within the matrix elements of NN and 3N interactions or the IMSRG evolution operator, and a means to reformulate the method that will let us exploit them.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Microscopic origin of the high thermoelectric figure of merit of n -doped SnSe

Excellent thermoelectric performance in the out-of-layer n-doped SnSe has been observed experimentally [Chang et al., Science 360, 778-783 (2018)]. Though, a first-principles investigation of the dominant scattering mechanisms governing all thermoelectric transport properties is lacking. In the present work, by applying extensive first-principles calculations of electron-phonon coupling associated with parameterized calculation of the scattering by ionized impurities, we investigate the reasons behind the superior figure of merit as well as the enhancement of zT above 600 K in n-doped out-of-layer SnSe, as compared to p-doped SnSe with similar carrier densities. For the n-doped case, the relaxation time is dominated by ionized impurity scattering and increases with temperature, a feature that maintains the power factor at high values at higher temperatures and simultaneously causes the carrier thermal conductivity at zero electric current (κ el ) to decrease faster for higher temperatures, leading to an ultrahigh-zT = 3.1 at 807 K. We rationalize the roles played by κ el and κ 0 (the thermal conductivity due to carrier transport under isoelectrochemical conditions) in the determination of zT. Our results show the ratio between κ 0 and the lattice thermal conductivity indeed corresponds to the upper limit for zT, whereas the difference between calculated zT and the upper limit is proportional to κ el .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

The many faces of θ' -Al 2 Cu precipitates: Energetics of pristine and solute segregated Al/ θ' semi-coherent interfaces

θ'-Al 2 Cu precipitates in Al-Cu alloys have various distorted octagon shapes, which can be explained by the competition between {100} and {110} type semi-coherent interfaces with the Al matrix. While most prior studies on the semi-coherent Al/θ' interfaces have focused on the {100} orientation, little is known about the {110} interface. We have investigated the energetics of pristine and solute-segregated {110} semi-coherent Al/θ' interfaces with advanced characterization and first-principles studies. We report interfacial, strain, and solute segregation energetics of the {110} Al/θ' semi-coherent interface for 39 elements and compared them with previously reported values of the {100} interface. We discuss the atomic features and atomic local structures to identify similarities and differences between the two types of Al/θ' semi-coherent interfaces. Here, the isotropy in pristine Al/θ' semi-coherent interfacial energy and the anisotropy resulting from solute segregation provide insight into the formation of different types of θ' precipitate “faces” reported in the literature.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Confinement Effects on Proton Transfer in TiO 2 Nanopores from Machine Learning Potential Molecular Dynamics Simulations

Improved understanding of proton transfer in nanopores is critical for a wide range of emerging applications, yet experimentally probing mechanisms and energetics of this process remains a significant challenge. To help reveal details of this process, we developed and applied a machine learning potential derived from first-principles calculations to examine water reactivity and proton transfer in TiO 2 slit-pores. Here, we find that confinement of water within pores smaller than 0.5 nm imposes strong and complex effects on water reactivity and proton transfer. Although the proton transfer mechanism is similar to that at a TiO 2 interface with bulk water, confinement reduces the activation energy of this process, leading to more frequent proton transfer events. This enhanced proton transfer stems from the contraction of oxygen–oxygen distances dictated by the interplay between confinement and hydrophilic interactions. Our simulations also highlight the importance of the surface topology, where faster proton transport is found in the direction where a unique arrangement of surface oxygens enables the formation of an ordered water chain. In a broader context, our study demonstrates that proton transfer in hydrophilic nanopores can be enhanced by controlling pore size, surface chemistry, and topology.

36 MATERIALS SCIENCE↗
DOE OSTI2022

A comprehensive and fair comparison of two neural operators (with practical extensions) based on $\mathrm{FAIR}$ data

Neural operators can learn nonlinear mappings between function spaces and offer a new simulation paradigm for real-time prediction of complex dynamics for realistic diverse applications as well as for system identification in science and engineering. Herein, we investigate the performance of two neural operators, which have shown promising results so far, and we develop new practical extensions that will make them more accurate and robust and importantly more suitable for industrial-complexity applications. The first neural operator, DeepONet, was published in 2019 (Lu et al., 2019), and its original architecture was based on the universal approximation theorem of Chen & Chen (1995). The second one, named Fourier Neural Operator or FNO, was published in 2020, and it is based on parameterizing the integral kernel in the Fourier space. DeepONet is represented by a summation of products of neural networks (NNs), corresponding to the branch NN for the input function and the trunk NN for the output function; both NNs are general architectures, e.g., the branch NN can be replaced with a CNN or a ResNet. According to Kovachki et al. (2021), FNO in its continuous form can be viewed conceptually as a DeepONet with a specific architecture of the branch NN and a trunk NN represented by a trigonometric basis. In order to compare FNO with DeepONet computationally for realistic setups, we develop several extensions of FNO that can deal with complex geometric domains as well as mappings where the input and output function spaces are of different dimensions. We also develop an extended DeepONet with special features that provide inductive bias and accelerate training, and we present a faster implementation of DeepONet with cost comparable to the computational cost of FNO, which is based on the Fast Fourier Transform. Here we consider 16 different benchmarks to demonstrate the relative performance of the two neural operators, including instability wave analysis in hypersonic boundary layers, prediction of the vorticity field of a flapping airfoil, porous media simulations in complex-geometry domains, etc. We follow the guiding principles of FAIR (Findability, Accessibility, Interoperability, and Reusability) for scientific data management and stewardship. The performance of DeepONet and FNO is comparable for relatively simple settings, but for complex geometries the performance of FNO deteriorates greatly. We also compare theoretically the two neural operators and obtain similar error estimates for DeepONet and FNO under the same regularity assumptions.

42 ENGINEERING↗
DOE OSTI2026

From Spin to Pseudospin Symmetry: The Origin of Magic Numbers in Nuclear Structure

Magic numbers lie at the heart of nuclear structure, reflecting enhanced stability in nuclei with closed shells. While the emergence of magic numbers beyond 20 is commonly attributed to strong spin-orbit coupling, the microscopic origin of the spin-orbit potential remains elusive, owing to its dependence on the resolution scale and renormalization scheme of nuclear forces. Here, we investigate the evolution of nuclear shell structure with varying momentum resolution in nuclear interactions derived from chiral effective field theory, using the similarity renormalization group to link different scales. We uncover a novel transition from spin symmetry to pseudospin symmetry as the resolution scale decreases, during which magic numbers emerge naturally. A similar pattern is found in calculations using relativistic one-boson-exchange potentials, underscoring the robustness of the phenomenon. This establishes a direct connection between realistic nuclear forces with a high resolution scale and effective nuclear forces at coarse-grained scales, offering a first-principles explanation for the origin of magic numbers and pseudospin symmetry in nuclear shell structure and new insights into the structure of exotic nuclei far from stability

Energy levels↗
DOE OSTI2020

Atomistic simulations of the thermal conductivity of liquids

We present a method based on sinusoidal approach to equilibrium molecular dynamics (SAEMD) to compute the thermal conductivity of liquids Similar to nonequilibrium molecular dynamics, and unlike equilibrium simulations based on the Green-Kubo formalism, the method only requires the calculation of forces and total energies. The evaluation of heat fluxes and energy densities is not necessary, thus offering the promise of efficiently implementing first principles simulations based on density functional theory or deep molecular dynamics. Our approach is a generalization of SAEMD for solids, where the thermal conductivity is computed in the steady state, instead of a transient regime, thus properly taking into account diffusive terms in the heat equation. We present results for liquid water at ambient conditions and under pressure and discuss simulation requirements to obtain converged values of the thermal conductivity as a function of size and simulation time.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Turboexpander for Direct Cooling in Hydrogen Vehicle Fueling Infrastructure

Hydrogen fuel cell electric vehicles (FCEVs) have been identified as one of a few options for zero carbon emissions transportation. A major advantage of FCEVs is that they can fuel quickly and follow a familiar fueling behavior to hydrocarbon-fueled vehicles. Whether light duty or heavy duty, the goal for a hydrogen dispenser is to fuel a vehicle in the same amount of time as the fossil fuel equivalent. When hydrogen is dispensed into the vehicle storage system, however, the temperature rises due to the Joule-Thomson effect and the heat of compression. Typically, vehicles store the compressed hydrogen in composite overwrapped pressure vessels that have a polymer liner with an operational temperature limit of 85°C. This temperature limit can be exceeded during fast fueling if hydrogen is not precooled. Precooling allows for a dispenser to fuel a vehicle at a faster flow rate by preventing the storage tank on the vehicle from overheating. Fueling protocols and requirements are presented in SAE J2601 Fueling Protocols for Light Duty Gaseous Hydrogen Surface Vehicles [1]. A heavy-duty equivalent is under development with similar requirements for precooling. Currently, conventional precooling for light-duty vehicle refueling uses a heat exchanger and chiller to cool the hydrogen gas to -40°C before entering the vehicle. The precooling system represents a significant part of the station capital and operating costs, so if the cost of the precooling system can be reduced by improving its efficiency, the overall station capital and operating cost can be reduced. In this project, National Renewable Energy Laboratory (NREL) and Sandia National Laboratories (SNL) researchers teamed up to investigate the turboexpander precooling application. A turboexpander is a device that places a turbine in a flow path where a pressure differential can be attained. This expansion device will extract work and lower the temperature of the fluid as the pressure reduces. While initial calculations based on established principles showed potential for a turboexpander to generate cooled gas, much work needs to be done to prove the concept. Turboexpanders typically work best under steady state conditions, while the dispenser is a very dynamic flow system. Dynamic turboexpander systems have been proven, such as a turbocharger on a gasoline vehicle. The inlet pressure at a dispenser is also much higher than any other known turboexpander system but should behave similarly to higher density fluids at lower pressures. Having both performed initial calculations, NREL and SNL researchers teamed up to investigate the turboexpander precooling application further. A project was soon built around the idea with SNL performing system modeling using previously proven capabilities and NREL performing hardware characterization with established station capabilities. Creare LLC was contracted as the turbomachinery expert to design and build the concept device. Part way through the project, however, contracting issues with the funding partner caused the project to terminate early before building and characterizing the concept device. While the project could not continue, many key findings were already learned. This paper is a summary of those findings.

08 HYDROGEN↗
DOE OSTI2021

Density of Fe-Ni-C Liquids at High Pressures and Implications for Liquid Cores of Earth and the Moon

The presence of light elements in the metallic cores of the Earth, the Moon, and other rocky planetary bodies has been widely proposed. Carbon is among the top candidates in light of its high cosmic abundance, siderophile nature, and ubiquity in iron meteorites. It is, however, still controversial whether carbon-rich core compositional models can account for the seismic velocity observations within the Earth and lunar cores. In this paper we report the density and elasticity of Fe 90 Ni 10 -3 wt.% C and Fe 90 Ni 10 -5 wt.% C liquid alloys using synchrotron-based X-ray absorption experiments and first-principles molecular dynamics simulations. Our results show that alloying of 3 wt.% and 5 wt.% C lowers the density of Fe 90 Ni 10 liquid by ~2.9-3.1% at 2 GPa, and ~3.4-3.6% at 9 GPa. More intriguingly, our experiments and simulations both demonstrate that the bulk moduli of the Fe-Ni-C liquids are similar to or slightly higher than those of Fe-Ni liquids. Thus, the calculated compressional velocity ($v_p$) of Fe-Ni-C liquids are higher than that of pure Fe-Ni alloy, promoting carbon as a possible candidate to explain the elevated v p in the Earth's outer core. However, the values and slopes of both density and v p of the studied two Fe-Ni-C liquids do not match the outer core seismic models, suggesting that carbon may not be the sole principal light element in Earth's outer core. The high $v_p$ of Fe-Ni-C liquids does not match the presumptive $v_p$ of the lunar outer core well, indicating that carbon is less likely to be its dominant light element.

58 GEOSCIENCES↗
DOE OSTI2022

First-principles investigation of phase stability in layered Na x ⁢CrO 2

Layered oxide intercalation compounds continue to attract interest as electrode materials for Na-ion batteries. However, many of these materials undergo complex phase transitions during cycling that influence battery performance but are still not completely understood. We have conducted a first-principles study of layered Na x ⁢CrO 2 (0 ≤ x ≤ 1) to assess phase stability between various Na-vacancy ordered phases in the O3 and P3 host structures. We predict that many of the low-energy phases belong to families of Na orderings that follow specific patterns. At high x, we identify families of vacancy row orderings in O3, which may also couple to magnetic orderings of the Cr spins. We predict similar orderings at intermediate x in P3 that contain antiphase boundaries between regions of the x = 1/2 ordering. In both cases, the average spacing between rows/boundaries is set by the overall composition. At x = 0, we find a strong preference for charge disproportionation and migration of Cr to tetrahedral sites in the intercalation layers. Finally, we obtain generally good agreement with experimental observations and rationalize key discrepancies.

25 ENERGY STORAGE↗
DOE OSTI2022

Tuning Spin-Orbit Torques Across the Phase Transition in VO 2 /NiFe Heterostructure

The emergence of spin-orbit torques as a promising approach to energy-efficient magnetic switching has generated large interest in material systems with easily and fully tunable spin-orbit torques. We report current-induced spin-orbit torques in VO 2 /NiFe heterostructures are investigated using spin-torque ferromagnetic resonance, where the VO 2 layer undergoes a prominent insulator-metal transition. A roughly twofold increase in the Gilbert damping parameter, α, with temperature is attributed to the change in the VO 2 /NiFe interface spin absorption across the VO 2 phase transition. More remarkably, a large modulation (±100%) and a sign change of the current-induced spin-orbit torque across the VO 2 phase transition suggest two competing spin-orbit torque generating mechanisms. The bulk spin Hall effect in metallic VO 2 , corroborated by the first-principles calculation of the spin Hall conductivity σ SH ≈ -10 4 ($\frac{\hbar}{e}$) Ω -1 m -1 , is verified as the main source of the spin-orbit torque in the metallic phase. The self-induced/anomalous torque in NiFe, with opposite sign and a similar magnitude to the bulk spin Hall effect in metallic VO 2 , can be the other competing mechanism that dominates as temperature decreases. For applications, the strong tunability of the torque strength and direction opens a new route to tailor spin-orbit torques of materials that undergo phase transitions for new device functionalities.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Stabilization of Dinuclear Rhodium and Iridium Clusters on Layered Titanate and Niobate Supports

Atomically dispersed organometallic clusters can provide well-defined nuclearity of active sites for both fundamental studies as well as new regimes of activity and selectivity in chemical transformations. More recently, dinuclear clusters adsorbed onto solid surfaces have shown novel catalytic properties resulting from the synergistic effect of two metal centers to anchor different reactant species. Difficulty in synthesizing, stabilizing, and characterizing isolated atoms and clusters without agglomeration challenges allocating catalytic performance to atomic structure. Here, we explore the stability of dinuclear rhodium and iridium clusters adsorbed onto layered titanate and niobate supports using molecular precursors. Both systems maintain their nuclearity when Statistical analysis of HAADF-STEM images revealed that rhodium and iridium dimers had mean cluster-to-cluster distances very similar to what is expected from a random distribution of atoms over a large area, indicating that they are dispersed without aggregation. The stability of dinuclear rhodium clusters supported on titanate nanosheets was also investigated by X-ray absorption fine structure (EXAFS), DRIFTS, and first-principles calculations. Both X-ray absorption spectroscopy and HAADF-STEM simulations, guided by density functional theory (DFT)-optimized structure models, suggested that rhodium dimers adsorb onto the nanosheets in an end-on binding mode that is stable up to 100 degrees C under reducing conditions. Finally, this study highlights that crystalline nanosheets derived from layered metal oxides can be used as model supports to selectively stabilize dinuclear clusters, which could have implications for heterogeneous catalysis.

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

Influence of near-surface oxide layers on TiFe hydrogenation: mechanistic insights and implications for hydrogen storage applications

The inevitable formation of passivating oxide films on the surface of the TiFe intermetallic compound limits its performance as a stationary hydrogen storage material. Extensive experimental efforts have been dedicated to the activation of TiFe, i.e. oxide layer removal prior to utilization for hydrogen storage. However, development of an efficient activation protocol necessitates a fundamental understanding of the composition and structure of the air-exposed surface and its interaction with hydrogen, which is currently absent. Therefore, in this study we explored the growth and nature of oxide films on the most exposed TiFe surface (110) in depth using static and dynamic first-principles methods. We identified the lowest energy structures for six oxygen coverages up to approximately 1.12 nm of thickness with a global optimization method and studied the temperature effects and structural evolution of the oxide phases in detail via ab initio molecular dynamics (AIMD). Based on structural similarity and coordination analysis, motifs for TiO 2 and TiFeO 3 as well as Ti(FeO 2 ) x (x = 2, 3 or 5) phases were identified. On evaluating the interaction of the oxidized surface with hydrogen, a minimal energy barrier of 0.172 eV was predicted for H 2 dissociation while H migration from the top of the oxidized surface to the bulk TiFe was limited by several high-lying energy barriers above 1.4 eV. Our mechanistic insights will prove themselves valuable for informed designs towards new activation methods of TiFe and related systems as hydrogen storage materials.

08 HYDROGEN↗
DOE OSTI2020

Ionization behavior of nanoporous polyamide membranes

Escalating global water scarcity necessitates high-performance desalination membranes, for which fundamental understanding of structure–property–performance relationships is required. In this study, we comprehensively assess the ionization behavior of nanoporous polyamide selective layers in state-of-the-art nanofiltration (NF) membranes. In these films, residual carboxylic acids and amines influence permeability and selectivity by imparting hydrophilicity and ionizable moieties that can exclude coions. We utilize layered interfacial polymerization to prepare physically and chemically similar selective layers of controlled thickness. Additionally, we then demonstrate location-dependent ionization of carboxyl groups in NF polyamide films. Specifically, only surface carboxyl groups ionize under neutral pH, whereas interior carboxyl ionization requires pH >9. Conversely, amine ionization behaves invariably across the film. First-principles simulations reveal that the low permittivity of nanoconfined water drives the anomalous carboxyl ionization behavior. Furthermore, we report that interior carboxyl ionization could improve the water–salt permselectivity of NF membranes over fourfold, suggesting that interior charge density could be an important tool to enhance the selectivity of polyamide membranes. Our findings highlight the influence of nanoconfinement on membrane transport properties and provide enhanced fundamental understanding of ionization that could enable novel membrane design.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗