Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “HYDRIDES”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

A Ni(II) Bis(diphosphine)-Hydride Complex Containing Proton Relays - Structural Characterization and Electrocatalytic Studies

The syntheses of the new 1,5-diphenyl-3,7-di(isopropyl)-1,5-diaza-3,7-diphosphacyclooctane ligand, PiPr2NPh2, is reported. The two equivalents of the ligand react with [Ni(CH3CN)6](BF4)2 to form the bis-diphosphine Ni(II)-complex [Ni(PiPr2NPh2)2](BF4)2, which acts as a proton reduction electrocatalyst. In addition to [Ni(PiPr2NPh2)2]2+, we report the syntheses and structural characterization of the Ni(0)-complex Ni(PiPr2NPh2)2, and the Ni(II)-hydride complex [HNi(PiPr2NPh2)2]BF4. The [HNi(PiPr2NPh2)2]BF4 complex represents the first Ni(II)-hydride in the [Ni(PR2NR'2)2]2+ family of compounds to be isolated and structurally characterized. In addition to the experimental data, the mechanism of electrocatalysis facilitated by [Ni(PiPr2NPh2)2]2+ is analyzed using linear free energy relationships recently established for the [Ni(PR2NR'2)2]2+ family. We thank Dr. Aaron Appel, Dr. Simone Raugei and Dr. Eric Wiedner for helpful discussions. This research was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. Mass spectrometry was provided at W. R. Wiley Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the Department of Energy’s office of Biological and Environmental Research located at Pacific Northwest National Laboratory. Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.

diphosphine↗
DOE OSTI2014

Production of Hydrogen by Electrocatalysis: Making the H-H Bond by Combining Protons and Hydrides

Generation of hydrogen by reduction of two protons by two electrons can be catalysed by molecular electrocatalysts. Determination of the thermodynamic driving force for elimination of H2 from molecular complexes is important for the rational design of molecular electrocatalysts, and allows the design of metal complexes of abundant, inexpensive metals rather than precious metals (“Cheap Metals for Noble Tasks”). The rate of H2 evolution can be dramatically accelerated by incorporating pendant amines into diphosphine ligands. These pendant amines in the second coordination sphere function as protons relays, accelerating intramolecular and intermolecular proton transfer reactions. The thermodynamics of hydride transfer from metal hydrides and the acidity of protonated pendant amines (pKa of N-H) contribute to the thermodynamics of elimination of H2; both of the hydricity and acidity can be systematically varied by changing the substituents on the ligands. A series of Ni(II) electrocatalysts with pendant amines have been developed. In addition to the thermochemical considerations, the catalytic rate is strongly influenced by the ability to deliver protons to the correct location of the pendant amine. Protonation of the amine endo to the metal leads to the N-H being positioned appropriately to favor rapid heterocoupling with the M-H. Designing ligands that include proton relays that are properly positioned and thermodynamically tuned is a key principle for molecular electrocatalysts for H2 production as well as for other multi-proton, multi-electron reactions important for energy conversions. The research was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. Pacific Northwest National Laboratory is operated by Battelle for DOE.

catalysis↗
DOE OSTI2014

Mechanistic Insights into Hydride Transfer for Catalytic Hydrogenation of CO2 with Cobalt Complexes

The catalytic hydrogenation of CO2 to formate by Co(dmpe)2H can proceeds via direct hydride transfer or via CO2 coordination to Co followed by reductive elimination of formate. Both pathways have activation barriers consistent with experiment (~17.5 kcal/mol). Controlling the basicity of Co by ligand design is key to improve catalysis. The research by N.K., D.M.C. and A.M.A. was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. The research by S.R. and M.D. was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science. Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for the DOE by Battelle.

Kumar, Neeraj↗
DOE OSTI2017

Interplay between Terminal and Bridging Diiron Hydrides in Neutral and Oxidized States

This study describes the structural, spectroscopic, and electrochemical properties of electronically unsymmetrical diiron hydrides. The terminal hydride Cp*Fe(pdt)Fe(dppe)(CO)H ([1(t-H)]0, Cp*– = Me5C5 –, pdt2– = CH2(CH2S–)2, dppe = Ph2PC2H4PPh2) was prepared by hydride reduction of [Cp*Fe(pdt)Fe(dppe)(CO)(NCMe)]+. As established by X-ray crystallography, [1(t- H)]0 features a terminal hydride ligand. Unlike previous examples of terminal diiron hydrides, [1(t-H)]0 does not isomerize to the bridging hydride [1(µ-H)]0. Oxidation of [1(t-H)]0 gives [1(t- H)]+, which was also characterized crystallographically as its BF4 – salt. Density functional theory (DFT) calculations indicate that [1(t-H)]+ is best described as containing an Cp*Fe(III) center. In solution, [1(t-H)]+ isomerizes to [1(µ-H)]+ as anticipated by DFT. Reduction of [1(µ- H)]+ by Cp2Co affords the diferrous bridging hydride [1(µ-H)]0. Electrochemical measurements and DFT calculations indicate that the couples [1(t-H)]+/0 and [1(µ-H)]+/0 differ by 210 mV. Qualitative measurements indicate that [1(t-H)]0 and [1(µ-H)]0 are close in free energy. Protonation of [1(t-H)]0 in MeCN solution affords H2 even with weak acids via hydride transfer.

Yu, Xin↗
DOE OSTI2018

Molecular dynamics studies of fundamental bulk properties of palladium hydrides for hydrogen storage

Solid-state hydrogen storage materials undergo complex phase transformations whose behavior are collectively determined by thermodynamic (e.g., Gibbs free energy), mechanical (e.g., lattice and elastic constants), and mass transport (e.g., diffusivity) properties. These properties depend on the reaction conditions and evolve continuously during (de)hydrogenation. Thus, they are difficult to measure in experiments. Because of this, past progress to improve solid-state hydrogen storage materials has been prolonged. Using PdH x as a representative example for interstitial metal hydride, we have recently applied molecular dynamics simulations to quantify hydrogen diffusion in the entire reaction space of temperature and composition. In this paper, we have further applied molecular dynamics simulations to obtain well-converged expressions for lattice constants, Gibbs free energies, and elastic constants of PdH x at various stages of the reaction. Finally, our studies confirm significant dependence of elastic constants on temperature and composition. Specifically, a new dynamic effect of hydrogen diffusion on elastic constants is discovered and discussed.

08 HYDROGEN↗
DOE OSTI2018

Benzimidazoles as Metal-Free and Recyclable Hydrides for CO 2 Reduction to Formate

We report a novel metal-free chemical reduction of CO 2 by a recyclable benzimidazole-based organo-hydride, whose choice was guided by quantum chemical calculations. Notably, benzimidazole-based hydride donors rival the hydride-donating abilities of noble-metal-based hydrides such as [Ru(tpy)(bpy)H] + and [Pt(depe) 2 H] + . Chemical CO 2 reduction to the formate anion (HCOO–) was carried out in the absence of biological enzymes, a sacrificial Lewis acid, or a base to activate the substrate or reductant. 13 CO 2 experiments confirmed the formation of H 13 COO – by CO 2 reduction with the formate product characterized by 1H NMR and 13C NMR spectroscopy and ESI-MS. The highest formate yield of 66% was obtained in the presence of potassium tetrafluoroborate under mild conditions. The likely role of exogenous salt additives in this reaction is to stabilize and shift the equilibrium toward the ionic products. After CO 2 reduction, the benzimidazole-based hydride donor was quantitatively oxidized to its aromatic benzimidazolium cation, establishing its recyclability. In addition, we electrochemically reduced the benzimidazolium cation to its organo-hydride form in quantitative yield, demonstrating its potential for electrocatalytic CO 2 reduction. These results serve as a proof of concept for the electrocatalytic reduction of CO 2 by sustainable, recyclable, and metal-free organo-hydrides.

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

Physical and Thermomechanical Properties of Yttrium Hydride from Large Scale Bulk Metal Hydriding Furnace

Given the superior thermal stability and highly attainable hydrogen density, yttrium hydride is an excellent high-temperature moderator material in advanced thermal neutron spectrum reactors that require small core volumes. Yttrium hydride has been selected as the moderator material for the Transformational Challenge Reactor, which was launched at Oak Ridge National Laboratory (ORNL) in 2019. However, fabrication of large-scale crack-free yttrium hydride is challenging and very limited efforts have been committed to the characterization of bulk yttrium hydride in response to the need to establish a complete database of the thermomechanical properties of YHx. In this report, the challenges associated with fabricating large-scale crack-free yttrium hydride are discussed herein. In response to those challenges, a hydriding system was designed and constructed at ORNL and was used to successfully fabricate crack-free yttrium hydride in complex geometries at large scales. This was accomplished by precisely controlling the hydrogen’s partial pressure and the retort temperature, which was informed by the well-established thermodynamic properties of the binary H-Y system. Hydrogen content in as-fabricated hydride was determined by the weight change method and vacuum hot extraction technique, complemented by the X-ray diffraction (XRD). In addition, significant efforts are being dedicated to establishing a complete database of the thermomechanical properties of as-fabricated yttrium hydride. In FY2020, we investigated the thermophysical properties of yttrium hydrides as a function of temperature (room temperature to 700°C) and hydrogen concentration (H/Y ratio ranges from 1.52 to 1.93). The results indicate that at the temperatures below 300 °C, the hydrogen content did not have a significant influence on the thermal expansion, while the specific heat capacity, the thermal diffusivity, and the calculated thermal conductivity were slightly higher for the higher H/Y ratio. Between 300°C and 700 °C, a reversible second-order endothermic transition in all measured thermal properties was observed. It was also found that the onset temperatures of the observed transition varied, with the composition having inverse dependence on the hydrogen content. An attempt was made to explain the behavior of the thermophysical properties at higher temperatures by considering the order– disorder transition as a result of hydrogen redistribution. In addition, nanoindentation was employed to determine the elastic modulus and hardness and to capture the crystal orientation dependence of these parameters. Vickers hardness was also reported. The final section of the report introduces ongoing neutron irradiation campaign of yttrium hydride.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2014

Ductility Evaluation of As-Hydrided and Hydride Reoriented Zircaloy-4 Cladding under Simulated Dry-Storage Condition

Pre-storage drying-transfer operations and early stage storage expose cladding to higher temperatures and much higher pressure-induced tensile hoop stresses relative to normal operation in-reactor and pool storage under these conditions. Radial hydrides could precipitate during slow cooling and provide an additional embrittlement mechanism as the cladding temperature decreases below the ductile-to-brittle transition temperature. As a means of simulating this behavior, unirradiated hydrided Zircaloy-4 samples were fabricated by a gas charging method to levels that encompass the range of hydrogen concentrations observed in current used fuel. Mechanical testing was carried out by the ring compression test (RCT) method at various temperatures to evaluate the sample s ductility for both as-hydrided and post-hydride reorientation treated specimens. As-hydrided samples with higher hydrogen concentration (>800 ppm) resulted in lower strain before fracture and reduced maximum load. Increasing RCT temperatures resulted in increased ductility of the as-hydrided cladding. A systematic radial hydride treatment was conducted at various pressures and temperatures for the hydrided samples with H content around 200 ppm. Following the radial hydride treatment, RCTs on the hydride reoriented samples were conducted and exhibited lower ductility compared to as-hydrided samples.

Yan, Yong↗
DOE OSTI2025

Elucidation of Marcus Relationships for Hydride Transfer Reactions Involving Transition Metal Hydrides

The rate of hydride transfer from three Ir hydride complexes of the type Cp*Ir( R bpy)H + (Cp* = C 5 Me 5 ; R bpy = 4,4′-R-2,2′-bipyridine, R = OMe, H, CO 2 Me) to six N-methylacridinium ( R Acr + ) acceptors with electronically different substituents in the 2- or 2,7-positions were measured. Using the thermodynamic hydricity of the donors and the hydride affinity of the acceptors the thermodynamic driving forces for hydride transfer were determined. Brønsted plots, which correlate kinetic and thermodynamic hydricity, demonstrate distinct linear free energy relationships for each complex, with different Brønsted α values. Thus, at the same driving force hydride transfer from Cp*Ir( OMe bpy)H + is faster than for Cp*Ir(bpy)H + or Cp*Ir( CO2Me bpy)H + . Experimental and computational analyses are consistent with a concerted hydride transfer mechanism for all Ir complexes. As the thermodynamic driving force increases an earlier transition state is observed and all transition states also include π-stacking interactions between the donor and acceptor, which likely contribute to the different α values. The experimental data fits well to the Marcus model, enabling the determination of reorganization energies (λ) that range from 58 to 69 kcal mol -1 . These are lower than λ values for hydride transfer reactions involving organic donors and acceptors. This work provides a rare example of the correlation of kinetic and thermodynamic hydricity using only experimental data and shows that hydride transfer reactions involving metal hydrides can follow Marcus theory. Furthermore, the findings offer insight into controlling metal-catalyzed hydride transfer reactions, which is valuable for designing improved systems for a range of transformations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Microstructure investigations of Yb- and Bi-doped Mg{sub 2}Si prepared from metal hydrides for thermoelectric applications

Within the field of thermoelectric materials for energy conversion magnesium silicide, Mg{sub 2}Si, is an outstanding candidate due to its low density, abundant constituents and low toxicity. However electronic and thermal tuning of the material is a required necessity to improve its Figure of Merit, zT. Doping of Yb via reactive YbH{sub 2} into the structure is performed with the goal of reducing the thermal conductivity. Hydrogen is released as a by-product at high temperatures allowing for facile incorporation of Yb into the structure. We report on the properties of Yb- and Bi-doped Mg{sub 2}Si prepared with MgH{sub 2} and YbH{sub 2} with the focus on the synthetic conditions, and samples’ microstructure, investigated by various electron microscopy techniques. Yb is found in the form of both Yb{sub 3}Si{sub 5} inclusions and Yb dopant segregated at the grain boundary substituting for Mg. The addition of 1 at% Yb concentration reduced the thermal conductivity, providing a value of 30 mW/cm K at 800 K. In order to adjust carrier concentration, the sample is additionally doped with Bi. The impact of the microstructure on the transport properties of the obtained material is studied. Idealy, the reduction of the thermal conductivity is achieved by doping with Yb and the electronic transport is adjusted by doping with Bi. Large grain microstructure facilitates the electronic transport. However, the synthetic conditions that provide the optimized microstructure for electrical transport do not facilitate the additional Yb dopant incorporation. Therefore, the Yb and Bi containing sample with the optimized microstructure provides a zT=0.46 at 800 K. - Graphical abstract: 1% or less addition of YbH{sub 2} to Mg{sub 2}Si significantly reduces the thermal conductivity of the material. Yb replaces some Mg in Mg{sub 2}Si and the remainder is distributed as Yb{sub 3}Sb{sub 5} in the Yb-doped Mg{sub 2}Si matrix. Correlation between the observed grain size and transport show the difficulty in simultaneously reducing the thermal conductivity with optimal electronic properties.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Back to functional hydrides: Effects of neutron-irradiated microstructure on hydrogen retention in yttrium hydride

Functional hydrides are promising candidates for advanced nuclear reactors, particularly in portable or transportable applications, due to their high hydrogen-retention capabilities, enabling efficient neutron moderation, and compact reactor design. However, hydrogen mobility in hydrides at elevated irradiation temperatures poses significant technological challenges, necessitating a comprehensive understanding of their irradiation behavior. Furthermore, this study investigated the microstructural and chemical stability of neutron-irradiated yttrium hydrides to assess their hydrogen-retention capacity. A targeted literature review was also conducted to contextualize neutron-irradiation effects on functional hydrides with regards to structural stability and hydrogen retention. Experimental characterizations revealed that, at high temperatures, irradiated hydrides retained their phase stability, which was likely enhanced by irradiation-induced microstructure evolution. Notably, an amorphous yttrium and oxygen -rich surface layer was present at the free surface of the hydride. Its thickness decreased while a continuous crystalline Y-O-rich layer was formed with increasing neutron damage. Additionally, the number density of dislocation loops and cavities generally increased as a function of neutron dose. First-principles calculations of hydrogen behavior within yttrium vacancy clusters in yttrium hydrides demonstrated vacancy-size-dependent hydrogen stability and configuration, highlighting the role of vacancy geometry in regulating hydrogen retention. Thus, the presence of irradiation-induced dislocation loops and cavities were hypothesized to improve hydrogen retention. Collectively, these findings advance the understanding of hydride behavior under neutron irradiation as well as their technological readiness for portable or transportable nuclear reactors.

Defect clusters↗
DOE OSTI2026

Chemically Separable Ruthenium Hydride Isomers with Distinct Hydride Transfer Properties

Transition metal hydrides are key intermediates in biological and industrial catalysis, where control over hydride donor ability (hydricity) is essential for optimizing reactivity. Herein, we report a series of isomeric ruthenium hydrides in which the ligand trans to the ruthenium hydride bond–either an N-heterocyclic carbene or pyridine–modulates the thermodynamic hydricity by up to 8 kcal mol –1 . These hydrides exhibited distinct reactivity toward CO 2 and various organic hydride acceptors, enabling detailed kinetic and mechanistic analysis. Stopped-flow experiments, isotopic labeling, and computational studies supported an outer-sphere hydride transfer mechanism. Linear free energy relationships (LFERs) and Marcus relationships were utilized to correlate the changes in thermodynamics and kinetics, revealing that ligands with strong trans effects and trans influence can disrupt conventional scaling relationships, which can be a powerful strategy for promoting new reactivity paradigms in hydride transfer reactions.

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

Thermodynamic and kinetic hydricities of metal-free hydrides

Metal-free hydrides are of increasing research interest due to their roles in recent scientific advances in catalysis, such as hydrogen activation with frustrated Lewis pairs and electrocatalytic CO 2 reduction with pyridinium and other aromatic cations. The structural design of hydrides for specific applications necessitates the correct description of their thermodynamic and kinetic prowess using reliable parameters – thermodynamic hydricity (ΔG H – ) and nucleophilicity ( N ). This review summarizes reported experimental and calculated hydricity values for more than 200 metal-free hydride donors, including carbon-, boron-, nitrogen- and silicon-based hydrides. We describe different experimental and computational methods used to obtain these thermodynamic and kinetic parameters. Furthermore, tabulated data on metal-free hydrides are discussed in terms of structure–property relationships, relevance to catalysis and contemporary limitations for replacing transition-metal hydride catalysts. Lastly, several selected applications of metal-free hydrides in catalysis are described, including photosynthetic CO 2 reduction and hydrogen activation with frustrated Lewis pairs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗