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Using inspiration from biological cofactors, the reversible storage of hydrogen on a supporting dihydrazonopyrrole ligand enables catalytic hydrogenation reactivity with nickel.
Tandem catalysis involving simultaneous dihydrogen generation from a hydrogen carrier and substrate reduction on a heterogeneous catalyst provides unique opportunities for green chemistry synthesis under mild reaction conditions.
To help meet the need for inexpensive green fuels, we are working on wind turbine design optimization specifically for hydrogen production. We have thus far achieved a 1.53% decrease in LCOH as compared to a turbine optimized for LCOE using the same code, design variables, and models. We accomplished this by optimizing some components of the wind turbine tower, rotor, and drivetrain design with hydrogen production and costs in the design loop.
The desorption kinetics of molecular hydrogen (H{sub 2}) from silicon (001) surfaces exposed to aqueous hydrogen fluoride and remote hydrogen plasmas were examined using temperature programmed desorption. Multiple H{sub 2} desorption states were observed and attributed to surface monohydride (SiH), di/trihydride (SiH{sub 2/3}), and hydroxide (SiOH) species, subsurface hydrogen trapped at defects, and hydrogen evolved during the desorption of surface oxides. The observed surface hydride species were dependent on the surface temperature during hydrogen plasma exposure with mono, di, and trihydride species being observed after low temperature exposure (150 °C), while predominantly monohydride species were observed after higher temperature exposure (450 °C). The ratio of surface versus subsurface H{sub 2} desorption was also found to be dependent on the substrate temperature with 150 °C remote hydrogen plasma exposure generally leading to more H{sub 2} evolved from subsurface states and 450 °C exposure leading to more H{sub 2} desorption from surface SiH{sub x} species. Additional surface desorption states were observed, which were attributed to H{sub 2} desorption from Si (111) facets formed as a result of surface etching by the remote hydrogen plasma or aqueous hydrogen fluoride treatment. The kinetics of surface H{sub 2} desorption were found to be in excellent agreement with prior investigations of silicon surfaces exposed to thermally generated atomic hydrogen.
Laboratory measurements were made on the concentration and temperature fields of cryogenic hydrogen jets. Images of spontaneous Raman scattering from a pulsed planar laser sheet were used to measure the concentration and temperature fields from varied releases. Jets with up to 5 bar pressure, with near-liquid temperatures at the release point, were characterized in this work. This data is relevant for characterizing unintended leaks from piping connected to cryogenic hydrogen storage tanks, such as might be encountered at a hydrogen fuel cell vehicle fueling station. The average centerline mass fraction was observed to decay at a rate similar to room temperature hydrogen jets, while the half-width of the Gaussian profiles of mass fraction were observed to spread more slowly than for room temperature hydrogen. This suggests that the mixing and models for cryogenic hydrogen may be different than for room temperature hydrogen. Results from this work were also compared to a one-dimensional (streamwise) model. Good agreement was seen in terms of temperature and mass fraction. Furthermore, a validated version of this model will be exercised to quantitatively assess the risk at hydrogen fueling stations with cryogenic hydrogen on-site.
Measurements of equilibrium vapor pressures by effusion thermogravimetry and melting points by differential scanning calorimetry reveal that the melting temperature and equilibrium vapor pressures of 1,4-bis(phenylethynyl)benzene (DEB) do not vary monotonically with the hydrogenation extent. Contrary to intuition which suggests increasing volatility with hydrogenation, results indicate decreasing volatility for the first two hydrogenation steps before a non-monotonic upward trend, in which trans -isomers are less volatile. Insights on structural packing and functional groups were obtained from x-ray diffraction and infrared studies to shed light on the observed variation in the volatility of DEB with hydrogenation. Density functional theory calculations were performed to obtain molecular level information and to establish the thermodynamics of DEB hydrogenation reactions. A major factor influencing the observed melting points and volatility of the hydrogenated intermediate species is identified as the local attractive or repulsive carbon-hydrogen (CH) dipole interactions among the getter molecules in their respective crystal structures. As a result, such collective CH dipole interactions can be used to predict the trends in the volatilities of catalytic hydrogenation processes.
Understanding the interaction of hydrogen with microstructural features in metallic materials is crucial for designing hydrogen-resistant alloys. Although thermal desorption spectroscopy (TDS) is widely used for investigating the hydrogen binding behavior of various microstructural features, its application to face-centered cubic (fcc) metals and alloys that exhibit low hydrogen diffusivity is limited due to the lumped TDS desorption signals. This paper shows that, by coupling a Sofronis–McMeeking type hydrogen transport model with a microstructure-informed finite-element model, TDS data can be deconvoluted to reveal the underlying adsorption–diffusion–desorption processes, hydrogen diffusivity, and trap-binding energies. In conclusion, the austenitic steel SS316L in solution-annealed condition is used as a demonstration material, and we focused on investigating the interaction of deuterium (hydrogen isotope) with grain boundaries, which is difficult to investigate from experiments alone but critical for design of alloys for hydrogen infrastructure.
The hydrogenation of furfural to furfuryl alcohol on Pd(111), Cu(111) and Pt(111) is studied with both standard Density Functional Theory (DFT)-GGA functionals and with van der Waals-corrected density functionals. VdW-DF functionals, including optPBE, optB88, optB86b, and Grimme's method, are used to optimize the adsorption configurations of furfural, furfuryl alcohol, and related intermediates resulting from hydrogenation of furfural, and the results are compared to corresponding values determined with GGA functionals, including PW91 and PBE. On Pd(111) and Pt(111), the adsorption geometries of the intermediates are not noticeably different between the two classes of funcfionals, while on Cu(111), modest changes are seen in both the perpendicular distance and the orientation of the aromatic ring with respect to the planar surface. In general, the binding energies increase substantially in magnitude as a result of van der Waals contributions on all metals. In contrast, however, dispersion effects on the kinetics of hydrogenation are relatively small. It is found that activation barriers are not significantly affected by the inclusion of dispersion effects, and a Brensted-Evans-Polanyi relationship developed solely from PW91 calculations on Pd(111) is capable of describing corresponding results on Cu(111) and Pt(111), even when the dispersion effects are included. Finally, the reaction energies and barriers derived from the dispersion-corrected and pure GGA calculations are used to plot simple potential energy profiles for furfural hydrogenation to furfulyl alcohol on the three considered metals, and an approximately constant downshift of the energetics due to the dispersion corrections is observed.
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Understanding how to control the movement of protons and electrons is crucial to the design of fast, efficient electrocatalysts for hydrogen production and oxidation based on earth-abundant metals. Our work seeks to elucidate fundamental questions about proton movement. We have demonstrated that incorporating a pendant amine functioning as a proton relay in the second coordination sphere of a metal complex helps proton mobility, resulting in faster and more energy efficient catalysts. Proton transfer reactions are often rate limiting, and are influenced by several factors, such as pKa values, steric effects, hydrogen bonding, and solvation/desolvation of the exogenous base and acid employed. The presence of multiple protonation sites introduces branching points along the catalytic cycle, making less productive pathways accessible, or leading to the formation of stable off-cycle species. Using ligands with only one pendant amine mitigates this problem and results in catalysts with high rates for production of H2. For H2 oxidation catalysts, iron complexes with a high H2 binding affinity were developed. However, the improvement of H2 binding enthalpy resulted in a pKa mismatch between the protonated metal center and the protonated pendant amine, and consequently to rate-limiting intramolecular proton movement. Taken altogether, our results demonstrate the necessity of optimizing the entire catalytic cycle, as the optimization of a specific catalytic step can negatively influence another step, and not necessarily lead to better catalytic performance. We discuss a general procedure, based on thermodynamic arguments, which allows the simultaneous minimization of the free energy change of each catalytic step, yielding a nearly flat free energy surface, with no large barriers due to energy mismatches from either high- or low-energy intermediates. 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 DOE.
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Due to the extreme chemical inertness of silicon carbide (SiC), in-situ thermal desorption is commonly utilized as a means to remove surface contamination prior to initiating critical semiconductor processing steps such as epitaxy, gate dielectric formation, and contact metallization. In-situ thermal desorption and silicon sublimation has also recently become a popular method for epitaxial growth of mono and few layer graphene. Accordingly, numerous thermal desorption experiments of various processed silicon carbide surfaces have been performed, but have ignored the presence of hydrogen, which is ubiquitous throughout semiconductor processing. In this regard, the authors have performed a combined temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS) investigation of the desorption of molecular hydrogen (H{sub 2}) and various other oxygen, carbon, and fluorine related species from ex-situ aqueous hydrogen fluoride (HF) and in-situ remote hydrogen plasma cleaned 6H-SiC (0001) surfaces. Using XPS, the authors observed that temperatures on the order of 700–1000 °C are needed to fully desorb C-H, C-O and Si-O species from these surfaces. However, using TPD, the authors observed H{sub 2} desorption at both lower temperatures (200–550 °C) as well as higher temperatures (>700 °C). The low temperature H{sub 2} desorption was deconvoluted into multiple desorption states that, based on similarities to H{sub 2} desorption from Si (111), were attributed to silicon mono, di, and trihydride surface species as well as hydrogen trapped by subsurface defects, steps, or dopants. The higher temperature H{sub 2} desorption was similarly attributed to H{sub 2} evolved from surface O-H groups at ∼750 °C as well as the liberation of H{sub 2} during Si-O desorption at temperatures >800 °C. These results indicate that while ex-situ aqueous HF processed 6H-SiC (0001) surfaces annealed at <700 °C remain terminated by some surface C–O and Si–O bonding, they may still exhibit significant chemical reactivity due to the creation of surface dangling bonds resulting from H{sub 2} desorption from previously undetected silicon hydride and surface hydroxide species.
We report quantifying the strengths of different types of hydrogen bonds in hydrogen bond networks (HBNs) via measurement of the adiabatic electron detachment energy of the conjugate base of a small covalent polyol model compound (i.e., (HOCH2CH2CH(OH)CH2)2CHOH) in the gas phase and the pKa of the corresponding acid in DMSO. The latter result reveals that the hydrogen bonds to the charged center and those that are one solvation shell further away (i.e., primary and secondary) provide 5.3 and 2.5 pKa units of stabilization per hydrogen bond in DMSO. Computations indicate that these energies increase to 8.4 and 3.9 pKa units in benzene and that the total stabilizations are 16 (DMSO) and 25 (benzene) pKa units. Calculations on a larger linear heptaol (i.e., (HOCH2CH2CH(OH)CH2CH(OH)CH2)2CHOH) reveal that the terminal hydroxyl groups each contribute 0.6 pKa units of stabilization in DMSO and 1.1 pKa units in benzene. All of these results taken together indicate that the presence of a charged center can provide a powerful energetic driving force for enzyme catalysis and conformational changes such as in protein folding due to multiple hydrogen bonds in a HBN.
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