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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Water Structure Controls Carbonic Acid Formation in Adsorbed Water Films

Reaction pathways and kinetics in highly structured H2O adsorbed as Ångstroms to nanometers thick layers on mineral surfaces are distinct from those facilitated by bulk liquid water. We investigate the role of interfacial H2O structure in the reaction of H2O and CO2 to form carbonic acid (H2CO3) in thin H2O films condensed onto silica nanoparticles from humidified supercritical CO2. Rates of carbonic acid formation are correlated to spectroscopic signatures of H2O structure using oxygen isotopic tracers and infrared spectroscopy. While carbonic acid virtually does not form in the supercritical phase, the silica surface catalyzes this reaction by concentrating H2O through adsorption at hydrophilic silanol groups. Within measurement uncertainty, we found no evidence that carbonic acid forms when exclusively ice-like structured H2O is detected at the silica surface. Instead, formation of H2C18O16O2 from H218O and C16O2 was found to be linearly correlated with liquid-like structured H2O that formed on the ice-like layer.

Miller, Quin RS↗
DOE OSTI2018

Hybrid Polymer/Metal–Organic Framework Films for Colorimetric Water Sensing over a Wide Concentration Range [Hybrid Polymer/MOF Films for Colorimetric Water Sensing over a Wide Concentration Range]

Because of their extraordinary surface areas and tailorable porosity, metal–organic frameworks (MOFs) have the potential to be excellent sensors of gas-phase analytes. MOFs with open metal sites are particularly attractive for detecting Lewis basic atmospheric analytes, such as water. Here, we demonstrate that thin films of the MOF HKUST-1 can be used to quantitatively determine the relative humidity (RH) of air using a colorimetric approach. HKUST-1 thin films are spin-coated onto rigid or flexible substrates and are shown to quantitatively determine the RH within the range of 0.1–5% RH by either visual observation or a straightforward optical reflectivity measurement. At high humidity (>10% RH), a polymer/MOF bilayer is used to slow the transport of H 2 O to the MOF film, enabling quantitative determination of RH using time as the distinguishing metric. Lastly, the sensor is combined with an inexpensive light-emitting diode light source and Si photodiode detector to demonstrate a quantitative humidity detector for low humidity environments.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Water-Fed Hydroxide Exchange Membrane Electrolyzer Enabled by a Fluoride-Incorporated Nickel–Iron Oxyhydroxide Oxygen Evolution Electrode

Here, we have developed a dissolved oxygen and galvanic corrosion method to synthesize vertically aligned fluoride-incorporated nickel–iron oxyhydroxide nanosheet arrays on a compressed Ni foam as an efficient self-supported oxygen evolution electrode. It is integrated with poly(aryl piperidinium) hydroxide exchange membrane and ionomers with high ion exchange capacity into a hydroxide exchange membrane electrolyzer fed with pure water, which achieves a performance of 1020 mA cm –2 at 1.8 V and prevents the detachment of catalysts during continuous operation (>160 h at 200 mA cm –2 ). Furthermore, this work provides a potential pathway for massively producing low-cost hydrogen using intermittent renewable energy sources.

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

Interfacial Reactivity and Speciation Emerging from Na-Montmorillonite Interactions with Water and Formic Acid at 200 °C: Insights from Reactive Molecular Dynamics Simulations, Infrared Spectroscopy, and X-ray Scattering Measurements

Reactive organic fluid - mineral interactions at elevated temperatures contribute to the evolution of planetary matter. One of the less studied but important transformations in this regard involves the reactions of formic acid with naturally occurring clays such as sodium montmorillonite. To advance a mechanistic understanding of these interactions, we use ReaxFF reactive molecular dynamics simulations in conjunction with infrared (IR) spectroscopy and X-ray scattering experiments to investigate the speciation behavior of water-formic acid mixtures on sodium montmorillonite interfaces at 473 K and 1 atm. Using a newly developed reactive forcefield, we show that the experimental IR spectra of unreacted and reacted mixture can be accurately reproduced by ReaxFF/MD. We further benchmark the simulation predictions of sodium carbonate and bicarbonate formation in the clay interlayers using Small and Wide-Angle X-ray Scattering measurements. Subsequently, leveraging the benchmarked forcefield, we interrogate the pathway of speciation reactions with emphasis on carbonate, formate, and hydroxide groups elucidating the energetics, transition states, intermediates, and preferred products. Further, we also delineate the differences in reactivities and catalytic effects of clay edges, facets, and interlayers owing to their local chemical environments, which have far reaching consequences in their speciation behavior. The experimental and simulation approaches described in this study and the transferable forcefields can be applied translationally to advance the science of clay-fluid interactions for several applications including subsurface fluid storage and recovery and clay-pollutant dynamics.

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

General Kinetic Model for pH Dependence of Proton-Coupled Electron Transfer: Application to an Electrochemical Water Oxidation System

The pH dependence of proton-coupled electron transfer (PCET) reactions, which are critical to many chemical and biological processes, is a powerful probe for elucidating their fundamental mechanisms. Herein, a general, multichannel kinetic model is introduced to describe the pH dependence of both homogeneous and electrochemical PCET reactions. According to this model, a weak pH dependence can arise from the competition among multiple sequential and concerted PCET channels involving different forms of the redox species, such as protonated and deprotonated forms, as well as different proton donors and acceptors. The contribution of each channel is influenced by the relative populations of the reactant species, which often depend strongly on pH, leading to complex pH dependence of PCET apparent rate constants. This model is used to explain the origins of the experimentally observed weak pH dependence of the electrochemical PCET apparent rate constant for a ruthenium-based water oxidation catalyst attached to a tin-doped In2O3 (ITO) surface. The weak pH dependence is found to arise from the intrinsic differences in the rate constants of participating channels and the dependence of their relative contributions on pH. This model predicts that the apparent maximum rate constant will become pH-independent at higher pH, which is confirmed by experimental measurements. Our analysis also suggests that the dominant channels are electron transfer at lower pH and sequential PCET via electron transfer followed by fast proton transfer at higher pH. Furthermore, this work highlights the importance of considering multiple competing channels simultaneously for PCET processes.

Catalysts↗
DOE OSTI2012

Incorporating Amino Acid Esters into Catalysts for Hydrogen Oxidation: Steric and Electronic Effects and the Role of Water as a Base

Four derivatives of a hydrogen oxidation catalyst, [Ni(P Cy 2 N Bn-R 2 ) 2 ] 2+ (Cy = cyclohexyl, Bn = benzyl, R = OMe, COOMe, CO-alanine-methyl ester, CO-phenylalanine-methyl ester), have been prepared to investigate steric and electronic effects on catalysis. Each complex was characterized spectroscopically and electrochemically, and thermodynamic data were determined. Crystal structures are also reported for the -OMe and -COOMe derivatives. All four catalysts were found to be active for H 2 oxidation. The methyl ester (R = COOMe) and amino acid ester containing complexes (R = CO-alanine-methyl ester or CO-phenylalanine-methyl ester) had rates slower (4 s –1 ) than that of the parent complex (10 s –1 ), in which R = H, which is consistent with the lower amine pK a 's and less favorable ΔG H 2 's found for these electron-withdrawing substituents. Dynamic processes for the amino acid ester containing complexes were also investigated and found not to hinder catalysis. The electron-donating methyl ether derivative (R = OMe) was prepared to compare electronic effects and has a catalytic rate similar to that of the parent complex. In the course of these studies, it was found that water could act as a weak base for H 2 oxidation, although catalytic turnover requires a higher potential and utilizes a different sequence of catalytic steps than when using a base with a higher pK a . Finally and importantly, these catalysts provide a foundation upon which larger peptides can be attached to [Ni(P Cy 2 N Bn 2 ) 2 ] 2+ hydrogen oxidation catalysts in order to more fully investigate and implement the effects of the outer coordination sphere.

amino acid catalysts↗
DOE OSTI2012

Distant protonated pyridine groups in water-soluble iron porphyrin electrocatalysts promote selective oxygen reduction to water

Fe(III)-meso-tetra(pyridyl)porphines are selective electrocatalysts for the reduction of dioxygen to water in aqueous acidic solution. The 2-pyridyl derivatives, both the triflate and chloride salts, are more selective than the isomeric 4-pyridyl complexes. The improved selectivity of is ascribed to the inward-pointing pyridinium groups acting as intramolecular proton relays. This research was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

Matson, Benjamin D↗
DOE OSTI2013

Communication: Energy benchmarking with quantum Monte Carlo for water nano-droplets and bulk liquid water

In this work, we show the feasibility of using quantum Monte Carlo (QMC) to compute benchmark energies for configuration samples of thermal-equilibrium water clusters and the bulk liquid containing up to 64 molecules. Evidence that the accuracy of these benchmarks approaches that of basis-set converged coupled-cluster calculations is noted. We illustrate the usefulness of the benchmarks by using them to analyze the errors of the popular BLYP approximation of density functional theory (DFT). Finally, the results indicate the possibility of using QMC as a routine tool for analyzing DFT errors for non-covalent bonding in many types of condensed-phase molecular system.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Rate Theory of Ion Pairing at the Water Liquid-Vapor Interface: A Case of Sodium Iodide

Studies of ion pairing at interfaces have been intensified recently because of their importance in many chemical reactive phenomena such as ion–ion interactions that are affected by interfaces and their influence on kinetic processes. In this study, we performed simulations to examine the thermodynamics and kinetics of small polarizable sodium iodide ions in the bulk and near the water liquid–vapor interface. Using classical transition state theory, we calculated the dissociation rates, and corrected them with transmission coefficients obtained from the reactive flux formalism and Grote-Hynes theory. Our results show that in addition to affecting the free energy of ions in solution, the interfacial environments significantly influence the kinetics of ion pairing. Results on the relaxation time obtained using the reactive flux formalism and Grote-Hynes theory present an unequivocal picture that the interface suppresses ion dissociation. The effects of the use of molecular models on the ion interactions as well as the ion-pair configurations at the interface also are quantified and discussed. Acknowledgments This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. The calculations were carried out using computer resources provided by the Office of Basic Energy Sciences.

Dang, Liem X.↗
DOE OSTI2013

Light Water Reactor Sustainability Program Support and Modeling for the Boiling Water Reactor Station Black Out Case Study Using RELAP and RAVEN

The existing fleet of nuclear power plants is in the process of extending its lifetime and increasing the power generated. In order to evaluate the impact of these two factors on the safety of the plant, the Risk Informed Safety Margin Characterization (RISMC) project aims to provide insight to decision makers through a series of simulations of the plant dynamics for different initial conditions (e.g., probabilistic analysis and uncertainty quantification). This report focuses, in particular, on the impact of power uprate on the safety of a boiled water reactor system. The case study considered is a loss of off-site power followed by the loss of diesel generators, i.e., a station black out (SBO) event. Analysis is performed by using a thermo-hydraulic code, i.e. RELAP-5, and a stochastic analysis tool currently under development at INL, i.e. RAVEN. Starting from the event tree models contained in SAPHIRE, we built the input file for RELAP-5 that models in great detail system dynamics under SBO conditions. We also interfaced RAVEN with RELAP-5 so that it would be possible to run multiple RELAP-5 simulation runs by changing specific keywords of the input file. We both employed classical statistical tools, i.e. Monte-Carlo, and more advanced machine learning based algorithms to perform uncertainty quantification in order to quantify changes in system performance and limitations as a consequence of power uprate. We also employed advanced data analysis and visualization tools that helped us to correlate simulation outcome such as maximum core temperature with a set of input uncertain parameters. Results obtained gave a detailed overview of the issues associated to power uprate for a SBO accident scenario. We were able to quantify how timing of safety related events were impacted by a higher reactor core power. Such insights can provide useful material to the decision makers to perform risk-infomed safety margins management.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗