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Results for “surface and interface chemistry”

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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Neutron and photon in-vivo materials characterization at the evolving plasma-material interface in plasma-burning fusion environments

This report includes the first set of MOSS data collected in the context of fusion-relevant plasma-material interactions. The data collected show that the surface curvature and stress irreversibly change during low-energy deuterium ion irradiation. This holds for both tungsten thin films, bulk tungsten, and single-crystal silicon. Meanwhile, argon irradiation did not produce this same effect. The surface morphology of the exposed samples was virtually identical regardless of gas species. There were, however, some surface chemistry differences between argon-exposed and deuterium-exposed samples, mainly concerning the oxide states of the W4f XPS signal. The changes in surface chemistry could be due to hydrogen dynamics on the tungsten surfaces, though further investigation will be required with in-situ irradiation and analysis. The changes in surface stress could also not be explained by temperature alone, as the temperature reached during the ion irradiations was too low to induce non-elastic strain. With this in mind, deuterium retention in the materials could change the surface curvature and stress. To confirm this, further work will be needed to quantify the change in curvature and relate it to ion flux, fluence, and deuterium retention. Unfortunately, when this work was conducted, the experimental setup for thermal desorption spectroscopy was not operating correctly, and that work could not be included in this dissertation. Despite experimental difficulties, this work shows the first results of a promising technique to study deuterium dynamics in tungsten-based reconstituted thin films.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Pb Sorption at the Barite (001)–Water Interface

Sorption of ions at the mineral-water interface is an important factor that determines the fate of toxic metals in the environment. Here, we use barite as a model substrate to understand the interaction of toxic-metal lead (Pb) with ionic crystals. The coverage and location of Pb sorbed to the (001) surface was measured as a function of aqueous Pb concentration ([Pb] aq ) using in situ specular resonant anomalous X-ray reflectivity (RAXR) to determine the sorption capacity and process. In this work, the results show that Pb sorption occurs via incorporation (primarily within the top barite layer similar to 3 angstrom in depth) and adsorption (mostly as an inner-sphere complex at similar to 2 angstrom in height) simultaneously. Both the incorporated and adsorbed Pb coverages increase with increasing [Pb] aq up to [Pb] aq similar to 200 mu M, above which the adsorbed fraction increases more rapidly than the incorporated fraction. This enhanced adsorption has a height distribution that is further extended (>= 15 angstrom from the surface) than that observed in lower [Pb] aq . This change in distribution is interpreted as arising from additional sorption of outer-sphere species or Pb-bearing phases precipitated on the surface. Desorption experiments in Pb-free solutions show that the incorporated fraction is more resistant to removal than the adsorbed fraction, consistent with the speciation-dependent stabilities premised in the classical sorption models.

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

Effect of Collective Dynamics and Anharmonicity on Entropy in Heterogenous Catalysis: Building the Case for Advanced Molecular Simulations

In this paper, we present a perspective on the computational determination of entropy and its effects and consequences on heterogeneous catalysis. Special attention is paid to the role of anharmonicity and the deviations from the standard harmonic oscillator approximations which can fail to provide a reliable assessment of entropy. To address these challenges, advanced methodologies are needed that can explicitly account for these thermodynamic drivers through the appropriate statistical sampling of reactive free energy surfaces. We discuss where anharmonicity should be expected, where it has been observed from a theoretical perspective, and the methods currently employed to address it. We concentrate on three types of systems where we have observed major, nonnegligible anharmonic effects: (1) supported nanoparticles, where the migration of metal atoms, complexes, and entire clusters exhibit anharmonic behavior in their dynamic motion; (2) porous solids where confinement effects distort potential energy surfaces and hinder molecular motions resulting in large entropic terms; and (3) solid/liquid interfaces, where interactions between solvent molecules and adsorbed species can result in large solvent organization free energy and unique reactivity.

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

Infrared spectroscopy data- and physics-driven machine learning for characterizing surface microstructure of complex materials

There is a need to characterize complex materials and their dynamics under reaction conditions to accelerate materials design. Adsorbate vibrational excitations are selective to adsorbate/surface interactions and infrared (IR) spectra associated with activating adsorbate vibrational modes are accurate, capture details of most modes, and can be obtained operando. Current interpretation depends on heuristic peak assignments for simple spectra, precluding the possibility of obtaining detailed structural information. Here, we combine data-based approaches with chemistry-dependent problem formulation to develop physics-driven surrogate models that generate synthetic IR spectra from first-principles calculations. Using synthetic IR spectra of carbon monoxide on platinum, we implement multinomial regression via neural network ensembles to learn probability distributions functions (pdfs) that describe adsorption sites and quantify uncertainty. We use these pdfs to infer detailed surface microstructure from experimental spectra and extend this methodology to other systems as a first step towards characterizing complex interfaces and closing the materials gap.

Science & Technology - Other Topics↗
DOE OSTI2021

Operando Topography and Mechanical Property Mapping of CO 2 Reduction Gas-Diffusion Electrodes Operating at High Current Densities

Electrochemical atomic force microscopy (EC-AFM) enables measurement of electrode topography and mechanical properties during electrochemical reactions. However, for aqueous-based reactions that make gas products, such as CO 2 reduction and water splitting into CO/H 2 , current densities below 1 mA cm −2 have been necessary to prevent formation of bubbles at the electrode; such bubbles can stick to the AFM probe and prevent further AFM imaging. Here, we demonstrate a novel cell design with a gas-diffusion electrode (GDE) to exhaust the gas products, thereby enabling high current density EC-AFM measurements at 1, 10, and 100 mA cm −2 that are not disturbed by bubble formation at the electrode surface. These experiments revealed a stable morphological structure of Cu catalysts deposited on GDEs during high current density operation. Systematic spatially resolved maps of deformation and adhesion showed no signs of a gas-liquid interface between catalyst particles of the GDE.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

The role of defects and solid/liquid interfacial interactions on controlling anisotropic growth of novel two-dimensional materials

Atomic-scale understanding about how interfacial properties are modified in the presence of defects and how they are correlated to the properties of nucleation and growth is critical for controlled materials growth on solid/liquid interfaces. The goal of this proposal is to establish preliminary data on the critical role of surface defects and chemical compositions of solvent on the structure, dynamics, reactivity, and free energetics at graphene/ionic liquid (IL) interfaces and their impact on two-dimensional (2D) growth of transition metal oxides on the surface. This study aims to develop generalized physical/chemical principles for directional growth at solid/liquid interfaces to achieve atomic-level control of two-dimensional materials synthesis. The proposed study of the effects of surface defects on the interfacial structure and reactivity will improve our understanding of the critical roles of heterogeneity, disorder, and solvents on 2D materials synthesis and lead to better control of directional growth of materials at solid/liquid interfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Elucidating Trivalent Ion Adsorption at Floating Carboxylic Acid Monolayers: Charge Reversal or Water Reorganization?

Here we study the adsorption of trivalent neodymium on floating arachidic acid films at the air–water interface by two complementary surface specific probes, sum frequency generation spectroscopy and X-ray fluorescence near total reflection. In the absence of background ions, neodymium ions compensate for the surface charge of the arachidic acid film at a bulk concentration of 50 μM without any charge reversal. Increasing the bulk concentration to 1 mM does not change the neodymium surface coverage but affects the interfacial water structure significantly. In the presence of a high concentration of NaCl, there is overcharging at 1 mM Nd 3+ , i.e., 30% more Nd 3+ than needed to compensate for the surface charge. These results show that the total coverage of neodymium ions is not enough to describe the complete picture at the interface, and interfacial water and ion coverage needs to be considered together to understand more complex ion adsorption and transport processes.

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

Na 3 Zr 2 Si 2 PO 12 Solid Electrolyte Membrane for High‐Performance Seawater Battery

Abstract Seawater batteries (SWBs) have gained tremendous interest in the electrochemical energy storage research field because of their low cost, natural abundance, and potential use for long‐duration energy storage. Advancing a SWB to demonstration projects is plagued by the poor electrochemical performance stemming from the poor interfaces of the solid electrolyte (SE), as well as the structural and chemical instabilities and sluggish ionic transport properties. In this study, the anode compartment of a surrogate SWB is constructed with a Na | SE | hard carbon configuration, and tailored dopants are introduced into the Nasicon‐type Na 3 Zr 2 Si 2 PO 12 (NZSP) SE membrane. After doping with TiO 2 , a much more densely packed pellet with uniformly distributed porous structure is obtained. Changes in surface chemistry and local structure in the bulk are observed, which are believed to contribute to the improved ionic conductivity and higher critical current density of the TiO 2 ‐doped NZSP. Stable cycling performance with reversible capacities based on different Na storage mechanisms are also demonstrated.

25 ENERGY STORAGE↗
DOE OSTI2022

Solvent-driven aqueous separations for hypersaline brine concentration and resource recovery

Solvent-driven separation processes can extract water and high-value minerals from high salinity or contaminated brines, simultaneously reducing the environmental impact of brine disposal and enabling resource recovery. The efficient dewatering of hypersaline brines is essential for the sustainable minimal and zero liquid discharge processing of industrial wastewaters. Fractional crystallization can selectively extract ions from contaminated waste streams, allowing critical materials to be recycled, including transition and lanthanide metals required for renewable energy generation and storage. Mass transfer in solvent-driven water extraction occurs across a liquid–liquid interface, eliminating the scaling and fouling of membrane and heat exchanger surfaces and limiting the need for extensive pretreatment. Solvent-driven fractional crystallization can leverage sequential treatment and control of process conditions to rapidly recover salts without requiring evaporation of water. Despite promising applications, the principles and potential of solvent-driven aqueous separations remain poorly understood. This critical review explores the opportunities presented by solvent-based aqueous separations from the molecular to process scale, evaluating the chemistry of solvation and system design in the broader context of desalination, resource recovery, water softening, and mineral production.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Projector-Free Capped-Fragment Scheme within Density Functional Embedding Theory for Covalent and Ionic Compounds

Quantum-mechanics-(QM)-based simulations now routinely aid in understanding and even discovering new chemistries involving molecules and materials exhibiting desired functionalities. Ab initio correlated wavefunction (CW) theories systematically improve QM methods, with many exhibiting high accuracy. However, execution of CW methods requires expensive computations that typically scale poorly with system size. Divide-and-conquer approaches partition large systems into smaller fragments; a lower level of theory treats fragment interactions while a preferred higher level of theory describes the important fragment. These methods offer ways to incorporate CWs into chemical simulations of large systems, e.g., biomolecules, surfaces, large inorganic clusters, bulk crystals, etc. Here we propose a partitioning protocol that utilizes capping atoms to saturate severed covalent bonds at fragment interfaces and density functional embedding theory (DFET) to describe fragment interactions. The capping groups in each fragment provide an ad-hoc potential that approximates the effects of the environment. An embedding potential optimized via DFET then serves as an augmentation of the capping group to simulate the effects of the environment. We concurrently use an auxiliary fragment (a separate system comprised of only the combined capping groups) to account for, and thereby correct, the electron density contributions of all the capping groups added to all of the fragments. This method depends only on the capped-subsystem and auxiliary-fragment electron densities, forgoing, as with the original DFET developed for metallic systems, orbital-based projector approaches that determine a nonlocal action of the embedding potential onto the fragment electrons. By using an auxiliary fragment, the method maintains a purely electron-density-dependent embedding potential, substantially lessening the cost and leading to simpler implementation. In this work, we demonstrate the utility of our capped-DFET and ensuing capped embedded CW method in two contrasting systems, namely, an organic molecule and an ionic metal oxide cluster.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

On the Origin of Sinter‐Resistance and Catalyst Accessibility in Raspberry‐Colloid‐Templated Catalyst Design

Abstract Nanoparticle (NP) sintering is a major cause of the deactivation of supported catalysts. Raspberry‐colloid‐templated (RCT) catalysts are an emerging class of materials that show an unprecedented level of sinter‐resistance and exhibit high catalytic activity. Here a comprehensive study of the origin of NP stability and accessibility in RCT catalysts using theoretical modeling, 3D electron microscopy, and epitaxial overgrowth is reported. The approach is showcased for silica‐based RCT catalysts containing dilute Pd‐in‐Au NPs previously used in hydrogenation and oxidation catalysis. Modeling of the contact line of the silica precursor infiltrating into the assembled raspberry colloids suggests that a large part of the particles must be embedded into silica, which is confirmed by quantitative visualization of >200 individual NPs by dual‐axis electron tomography. The RCT catalysts have a unique structure in which all NPs reside at the pore wall but have >50% of their surface embedded in the matrix, giving rise to the strongly enhanced thermal and mechanical stability. Importantly, epitaxial overgrowth of Ag on the supported NPs reveals that not only the NP surface exposed to the pore but the embedded interface as well remained chemically accessible. This mechanistic understanding provides valuable guidance in the design of stable catalytic materials.

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

Dynamics of Electric Polarization and Relaxation of Ions at Humid Calcite Surfaces

Mobile ions at mineral surfaces can respond to an applied electric field, adopting a new distribution that effectively represents polarization of the electrical double layer. When the field is released, the ions relax to their equilibrium distribution. In both cases, the dynamics are characteristic of the interface. However, current models of electrokinetic phenomena are not sufficiently robust to accurately predict collective ion dynamics at structurally and chemically specific mineral–water interfaces. Here, in this study, we use electrostatic force microscopy (EFM) to investigate the dynamics of ion relaxation at hydrated calcite (104) surfaces at controlled relative humidity (RH). Electrically biased probes are used to polarize the distributions of calcium and carbonate ions that are intrinsic to this interface across a range of RH values. Polarization kinetics are tracked by monitoring the tip–sample force gradient during charging, and EFM imaging is used to characterize the spatial relaxation dynamics after the applied field is released. Electrostatic finite element modeling of the sample/probe system across length-scales from nanometers to millimeters reproduces the observed stretched exponential charging response. Together, these results allow us to estimate the ion diffusivities at the interface across a wide range of RH values. These diffusivities increase by roughly 5 orders of magnitude as the RH is increased from 5 to 90%, highlighting the critical role of adsorbed water for surface ion solvation that enables ion mobility.

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

Air-Stable Calcium Cyanamide-Supported Ruthenium Catalyst for Ammonia Synthesis and Decomposition

Efficient ammonia synthesis and decomposition processes under mild conditions are important to meet the expanding demand in major applications of ammonia as the energy carrier and to provide feedstock for chemical industry. In this study, we report that air-stable calcium cyanamide-supported ruthenium (Ru/CaCN 2 ) works as an efficient and stable catalyst for ammonia synthesis and decomposition. Ru/CaCN 2 exhibits greater catalytic performances for both reactions than Ru/Ca 2 N electride and Ru–Cs/MgO. The kinetic analysis for ammonia synthesis suggests that Ru/CaCN 2 exhibits low apparent activation energy and high resistance to hydrogen poisoning, which has characteristics similar to the kinetic parameters of Ru-supported electride catalyst. H 2 -temperature programmed reaction and temperature programmed desorption revealed that Ru promoted the formation of CN 2 vacancies on the CaCN 2 surface which in turn capture hydrogen as H – ions during the reaction. Density functional theory calculations provide insights into how the formation of CN 2 vacancies is promoted by Ru, which leads to the decrease in the work function of the CaCN 2 surface and the hydrogen capture at the Ru-support interface. These results suggest that the high catalytic performance of Ru/CaCN 2 can be attributed to the formation of a quasi-electride structure at the Ru–CaCN 2 interface.

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

Effect of Co-Reactants on Interfacial Oxidation in Atomic Layer Deposition of Oxides on Metal Surfaces

We have examined the ALD of Al 2 O 3 using TMA as the precursor and t-BuOH and H 2 O as the co-reactants, focusing on the effects of the latter on both the ALD process and the possible modification of the underlying substrate. We have employed a quartz-crystal microbalance (QCM) to monitor ALD in situ and in real-time, and the deposited thin films have been characterized using X-ray photoelectron spectroscopy, spectroscopic ellipsometry, and X-ray reflectivity. Growth of thin films of Al 2 O 3 using TMA and either t-BuOH or H 2 O as the co-reactant at T = 285 °C produces thin films of similar physical properties (density, stoichiometry, minimal carbon incorporation), and the growth rate per cycle is similar for the two co-reactants at this temperature. At a lower temperature of T = 120 °C, the behavior is starkly different, where growth occurs with H 2 O but not with t-BuOH. At either process temperature, we find no evidence for significant coverages of a long-lived tert-butoxy species from the reaction of t-BuOH. Deposition of thin films of Al 2 O 3 on metal surfaces of Cu and Co has been examined for evidence of interfacial oxidation. While growth with either co-reactant does not lead to the oxidation of the underlying Cu substrate, use of H 2 O leads to the oxidation of Co, while use of t-BuOH as the co-reactant does not. Thermodynamic factors may affect early stages of growth as Al species will likely scavenge all free O species. In contrast, at later times diffusion of species through the deposited Al 2 O 3 thin film could result in oxidation at the Al 2 O 3 |metal interface, a process that is strongly hindered in the case of t-BuOH due to its size. Furthermore, this observation highlights the importance of the choice of the co-reactant concerning ALD of oxides on metal surfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Sodium electrochemical interfaces with NaSICON-type ceramics

The present invention is directed to the modification of sodium electrochemical interfaces to improve performance of NaSICON-type ceramics in a variety of electrochemical applications. Enhanced mating of the separator-sodium interface by means of engineered coatings or other surface modifications results in lower interfacial resistance and higher performance at increased current densities, enabling the effective operation of molten sodium batteries and other electrochemical technologies at low and high temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Solid-state polymer-particle hybrid electrolytes: Structure and electrochemical properties

Solid-state electrolytes (SSEs) are challenged by complex interfacial chemistry and poor ion transport through the interfaces they form with battery electrodes. Here, we investigate a class of SSE composed of micrometer-sized lithium oxide (Li 2 O) particles dispersed in a polymerizable 1,3-dioxolane (DOL) liquid. Ring-opening polymerization (ROP) of the DOL by Lewis acid salts inside a battery cell produces polymer-inorganic hybrid electrolytes with gradient properties on both the particle and battery cell length scales. These electrolytes sustain stable charge-discharge behavior in Li||NCM811 and anode-free Cu||NCM811 electrochemical cells. On the particle length scale, Li 2 O retards ROP, facilitating efficient ion transport in a fluid-like region near the particle surface. On battery cell length scales, gravity-assisted settling creates physical and electrochemical gradients in the hybrid electrolytes. By means of electrochemical and spectroscopic analyses, we find that Li 2 O particles participate in a reversible redox reaction that increases the effective CE in anode-free cells to values approaching 100%, enhancing battery cycle life.

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

Evaluating the effect of ionomer chemical composition in silver-ionomer catalyst inks toward the oxygen evolution reaction by half-cell measurements and water electrolysis

The effect of anion exchange ionomer (AEI) chemistry on the kinetics of the oxygen evolution reaction (OER) was systematically studied in both half-cell and single-cell electrolysis experiments. OER was studied in 1 M K 2 CO 3 at 50°C using an array of ionomer-silver catalyst inks deposited on Ni foam. Different ionomer modifications were investigated to optimize the OER performance. The AEI used in this work features a block copolymer backbone of polychloromethylstyrene-b-polycyclooctene-b-polychloromethylstyrene which was functionalized with either benzyltrimethylammonium (TMA) or benzylmethylpiperidinium (MPRD) quaternary ammonium cations. Here, using an MPRD quaternary ammonium cation shifted the rate determining step at high overpotentials, ultimately providing enhanced performance. Increasing the catalyst ink dilution was also found to substantially improve mass activity and catalyst utilization (increase from 35 to 88 A g –1 Ag), likely by reducing the ionomer thickness and decreasing transport resistances. In the final ionomer modification, the Ni foam substrate was leveraged to partially hydrogenate the polycyclooctene midblock to be polyethylene-like at the Ni interface. A significant increase in the electrochemical surface area (Cdl increased from 8.8 to 20.8 mF cm –2 ) and performance (by 47 mA cm –2 or 29 A g –1 Ag) was observed with the incorporation of polyethylene. Kinetic results from half-cell experiments were validated via single-cell anion exchange membrane electrolysis experiments, where the optimized electrode displayed enhanced performance in both 1 M K 2 CO 3 and DI H 2 O.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗