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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
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

3-Methyl-1,2-BN-Cyclopentane: A Promising H2 Storage Material?

We provide detailed characterization of properties for 3-methyl-1,2-BN-cyclopentane 1 that are relevant to H2 storage applications such as viscosity, thermal stability, H2 gas stream purity, and polarity. The viscosity of 1 at room temperature is 25±5 cP, about one fourth the viscosity of olive oil. TGA/MS analysis indicates that liquid carrier 1 is thermally stable at 30 °C but decomposes slowly at 50 °C. RGA data suggest that the H2 desorption from 1 is a clean process, producing relatively pure H2 gas. Compound 1 is a polar zwitterionic type liquid consistent with theoretical predictions and solvatochromic studies. "T.A. acknowledges support from the Fuel Cell Technology Program at U.S. DOE, Office of Energy Efficiency 65 and Renewable Energy. Pacific Northwest National Laboratory is operated by Battelle."

Luo, Wei↗
DOE OSTI2013

Production of H2 at Fast Rates Using a Nickel Electrocatalyst in Water/Acetonitrile Solutions

Efficient production of molecular hydrogen for storage of energy from renewable sources is crucial for the development of wind and solar power. Hydrogenase enzymes in nature catalyze H2 production using earth-abundant metals (iron and nickel) using precise delivery of protons to the metal center. Here we report a synthetic nickel complex containing proton relays, [Ni(PPh2NC6H4OH2)2](BF4)2 (PPh2NC6H4OH2 = 1,5-bis(p-hydroxyphenyl)-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane), that catalyzes the production of H2 in an aqueous environment with turnover frequencies of 750-170,000 s-1 at directly measured overpotentials of 310-470 mV. The remarkable performance of this catalyst in aqueous environments exceeds the requirements necessary for molecular catalytic production of H2 by energy derived from photovoltaic solar cells. 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. Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.

Hoffert, Wesley A.↗
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

A Proton Channel Allows a Hydrogen Oxidation Catalyst to Operate at a Moderate Overpotential with Water Acting as a Base

Proton channels facilitate the movement of protons over large distances and are critical in many reactions, from controlling proton delivery in metalloenzymes[1] to moving protons through PEM fuel cells.[2] Hydrogenases are enzymes that use proton channels to deliver protons to or from the enzyme active site to achieve high rates of hydrogen production and oxidation at low overpotentials.[3] The [Ni(PR2NR’2)2]2+ series of complexes, which are functional mimics of the [FeFe]-hydrogenase active site, utilize pendant amines to move the proton to or from the Ni, resulting in some of the fastest synthetic catalysts for hydrogen production and oxidation reported.[4] While intramolecular proton movement has been shown to be facile,[5] deprotonation of hydrogen oxidation catalysts can be a slow step for catalysis.[6] Additionally, a stable H2 adduct (endo-endo) is formed which, if bypassed, could contribute to an overall enhanced rate (Figure 1). A proton channel may aid in addressing these outstanding issues, and the well-studied nature of these catalysts allows them to serve as a platform to investigate the role of a proton channel in solving these problems. To this end we added a second proton relay to this complex, which we demonstrate serves two purposes: we show that the second proton relay facilitates rapid proton transfer, altering the kinetic products formed following H2 addition, and avoiding the low energy endo-endo intermediate. It also aids in lowering the overpotential at which the catalyst operates using water as a base, demonstrating the multi-functional role of a proton channel in molecular catalysts, and possibly in enzymes. This work was supported by the US Department of Energy, Early Career Research Program, Basic Energy Sciences, Chemical Sciences, Geosciences & Biosciences Division and by the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

amino acid catalysts↗
DOE OSTI2013

Calculation of the Gibbs Free Energy of Solvation and Dissociation of HCl in Water via Monte Carlo Simulations and Continuum Solvation Models

The free energy of solvation and dissociation of hydrogen chloride in water is calculated through a combined molecular simulation quantum chemical approach at four temperatures between T = 300 and 450 K. The free energy is first decomposed into the sum of two components: the Gibbs free energy of transfer of molecular HCl from the vapor to the aqueous liquid phase and the standard-state free energy of acid dissociation of HCl in aqueous solution. The former quantity is calculated using Gibbs ensemble Monte Carlo simulations using either Kohn-Sham density functional theory or a molecular mechanics force field to determine the system’s potential energy. The latter free energy contribution is computed using a continuum solvation model utilizing either experimental reference data or micro-solvated clusters. The predicted combined solvation and dissociation free energies agree very well with available experimental data. CJM was supported by the US Department of Energy,Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

McGrath, Matthew↗
DOE OSTI2014

Dissecting the steps of CO2 reduction: 2. The interaction of CO and CO2 with Pd/γ-Al2O3: an in situ FTIR study

Alumina supported Pd catalysts with metal loadings of 0.5, 2.5 and 10 wt% were investigated by in situ FTIR spectroscopy in order to understand the nature of adsorbed species formed during their exposure to CO2 and CO. Exposing the annealed samples to CO2 at 295 K resulted in the formation of alumina support-bound surface species only: linear adsorbed CO2, bidentate carbonates and bicarbonates. Room temperature exposure of all three samples to CO produced IR features characteristic of both ionic and metallic Pd, as well as bands we observed upon CO2 adsorption (alumina support-bound species). Low temperature (100 K) adsorption of CO on the three samples provided information about the state of Pd after oxidation and reduction. Oxidized samples contained exclusively ionic Pd, while mostly metallic Pd was present in the reduced samples. Subsequent annealing of the CO-saturated samples revealed the facile (low temperature) reduction of PdOx species by adsorbed CO. This process was evidenced by the variations in IR bands characteristic of ionic and metallic Pd-bound CO, as well as by the appearance of IR bands associated with CO2 adsorption as a function of annealing temperature. Samples containing oxidized Pd species (oxidized, annealed or reduced) always produced CO2 upon their exposure to CO, while CO2-related surface entities were observed on samples having only fully reduced (metallic) Pd. Acknowledgements: The catalyst preparation was supported by a Laboratory Directed Research and Development (LDRD) project. This work was supported by the US Department of Energy Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy. JHK also acknowledges the support of this work by the 2013 Research Fund of UNIST (Ulsan National Institute of Science and Technology, Ulsan, Korea).

CO and CO2 adsorption↗
DOE OSTI2014

Heterolytic Cleavage of H2 by Bifunctional Manganese(I) Complexes: Impact of Ligand Dynamics, Electrophilicity, and Base Positioning

We report the synthesis, characterization, and reactivity with H2 of a series of MnI complexes of the type [(P-P)Mn(L2)CO]+ (L2 = dppm, bppm, or (CO)2; P-P = PPhNMePPh or PPh2 NBn2 ) that bear pendant amine ligands designed to function as proton relays. The pendant amine was found to function as a hemilabile ligand; its binding strength is strongly affected by the ancillary ligand environment around Mn. Tuning the electrophilicity of the Mn center leads to systems capable of reversible heterolytic cleavage of the H-H bond. The strength of pendant amine binding can be balanced to protect the Mn center while still leading to facile reactivity with H2. Neutral amine-bearing MnIH species were found to react with one-electron oxidants and, after proton and electron transfer reactions, regenerate MnI cationic species. The reactivity presented herein indicate that the Mn complexes we have developed are a promising platform for Mn-based H2 oxidation electrocatalyst development. 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.

electrochemistry↗
DOE OSTI2015

Nickel Phosphine Catalysts with Pendant Amines for Electrocatalytic Oxidation of Alcohols

Nickel phosphine complexes with pendant amines have been found to be electrocatalysts for the oxidation of primary and secondary alcohols, with turnover frequencies as high as 3.3 s-1. These complexes are the first electrocatalysts for alcohol oxidation based on non-precious metals, which will be critical for use in fuel cells. The research by CJW, ESW, and AMA was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. The research by JASR 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 is operated by Battelle for the US Department of Energy.

Alcohol Oxidation↗
DOE OSTI2015

Covalent Attachment of Diphosphine Ligands to Glassy Carbon Electrodes via Cu-Catalyzed Alkyne-Azide Cycloaddition. Metallation with Ni(II)

Covalent tethering of PPh2NC6H4C=CH2 ligands (PPh2NC6H4C=CH2 = 1,5-di-(4-ethynylphenyl)-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane) to planar, azide-terminated glassy carbon electrode surfaces has been accomplished using a CuI-catalyzed alkyne-azide cycloaddition (CuAAC) as the coupling reaction, using a BH3?P protection-deprotection strategy. Deprotected, surface-confined ligands were metallated using [NiII(MeCN)6](BF4)2. X-ray photoelectron spectroscopic measurements demonstrate that metallation introduced 1.3 equivalents NiII per diphosphine onto the electrode surface. Exposure of the surface to a second diphosphine ligand, PPh2NPh2, resulted in the removal of Ni from the surface. Protection, coupling, deprotection, and metallation conditions were optimized using solution-phase model systems, with benzyl azide as a model for the azide-terminated carbon surface; these reactions generate a [NiII(diphosphine)2]2+ complex. Acknowledgment. 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. The XPS measurements were performed at the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the U. S. Department of Energy, Office of Science, Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. The x-ray crystal structure analysis was carried out by S.L., who was supported by a grant to Wendy J. Shaw from the Early Career Research Program through the U.S. Department of Energy, Office of Science. Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.

electrocatalysis, surface attachment, XPS↗
DOE OSTI2015

Water-Assisted Proton Delivery and Removal in bio-inspired Hydrogen Production Catalysts

Electrocatalysts for H2 production are envisioned to play an important role in renewable energy utilization systems. Nickel-based catalysts featuring pendant amines functioning as proton relays in the second coordination sphere of a metal center have led to catalysts achieving turnover frequencies as high as 107 s-1 for H2 production. The fastest rates are observed when water is present in solution, with rates up to 102 times faster than dry conditions. The focus of this paper is to provide mechanistic insight into the unexpected enhancement due to water. Addition of H2 to [Ni(PR2NR´2)2]2+ was previously shown to give three isomers of a Ni(0) product with two protonated amines, where the N-H can be endo or exo to the Ni. By investigating the deprotonation of two N-protonated Ni(0) intermediates resulting from H2 addition to to [Ni(PR2NR´2)2]2+, we observe an enhancement in the rate of deprotonation for protons positioned on the pendant amine next to the metal (endo) vs. protons that are positioned away from the metal (exo). Computational studies suggest that steric accessibility and desolvation energy of the deprotonating base are responsible for limiting endo deprotonation. The significant reduction in this barrier observed in the presence of water has important implications for disfavoring less productive catalytic pathways and increasing catalytic rates. 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. Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.

Ho, Ming-Hsun↗
DOE OSTI2015

Blending materials composed of boron, nitrogen and carbon to transform approaches to liquid hydrogen stores

Energy storage remains a key challenge for the advancement of fuel cell applications. Because of this, hydrogen has garnered much research attention for its potential as an energy carrier. This can be attributed to its abundance from non-petroleum sources, and its energy conversion efficiency. Our group, among others, has been studying the use of ammonia borane as a chemical hydrogen storage material for the past several years. Ammonia borane (AB, NH3BH3), a solid state complex composed of the light weight main group elements of nitrogen and boron, is isoelectronic with ethane and as such is an attractive hydrogen storage material with a high gravimetric capacity of H2 (19.6 wt%). However, the widespread use of AB as a chemical hydrogen storage material has been stalled by some undesirable properties and reactivity. Most notably, AB is a solid and this presents compatibility issues with the existing liquid fuel infrastructure. The thermal release of H2 from AB also results in the formation of volatile impurities (borazine and ammonia) that are detrimental to operation of the fuel cell. Additionally, the major products in the spent fuel are polyborazylene and amine borane oligomers that present challenges in regenerating AB. This research was funded by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy. The Pacific Northwest National Laboratory is operated by Battelle for DOE.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Re-Examining the Properties of the Aqueous Vapor-Liquid Interface Using Dispersion Corrected Density Functional Theory

First-principles molecular dynamics simulations, in which the forces are computed from electronic structure calculations, have great potential to provide unique insight into structure, dynamics, electronic properties, and chemistry at aqueous interfaces that is not available from empirical force fields. The majority of current first-principles simulations are driven by forces derived from density functional theory with generalized gradient approximations to the exchange-correlation energy, which do not capture dispersion interactions. We have carried out first-principles molecular dynamics simulations of air-water interfaces employing a particular generalized gradient approximation to the exchange-correlation functional (BLYP), with and without empirical dispersion corrections. We assess the utility of the dispersion corrections by comparison of a variety of structural, dynamic, and thermodynamic properties of bulk and interfacial water with experimental data, as well as other first-principles and force field-based simulations. This work was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

1ST PRINCIPLES↗
DOE OSTI2012

The outer-coordination sphere: incorporating amino acids and peptides as ligands for homogeneous catalysts to mimic enzyme function

Great progress has been achieved in the field of homogeneous transition metal-based catalysis, however, as a general rule these solution based catalysts are still easily outperformed, both in terms of rates and selectivity, by their analogous enzyme counterparts, including structural mimics of the active site. This observation suggests that the features of the enzyme beyond the active site, i.e. the outer-coordination sphere, are important for their exceptional function. Directly mimicking the outer-coordination sphere requires the incorporation of amino acids and peptides as ligands for homogeneous catalysts. This effort has been attempted for many homogeneous catalysts which span the manifold of catalytic reactions and often require careful thought regarding solvent type, pH and characterization to avoid unwanted side reactions or catalyst decomposition. This article reviews the current capability of synthesizing and characterizing this often difficult category of metal-based catalysts. This work was funded by the DOE Office of Science Early Career Research Program through the Office of Basic Energy Sciences. Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.

catalysis, outer-coordination sphere, bioinspired ↗