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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Application of machine learning to discover new intermetallic catalysts for the hydrogen evolution and the oxygen reduction reactions

The adsorption energies for hydrogen, oxygen, and hydroxyl were calculated by means of density functional theory on the lowest energy surface of 24 pure metals and 332 binary intermetallic compounds with stoichiometries AB, A 2 B, and A 3 B taking into account the effect of biaxial elastic strains. This information was used to train two random forest regression models, one for the hydrogen adsorption and another for the oxygen and hydroxyl adsorption, based on 9 descriptors that characterized the geometrical and chemical features of the adsorption site as well as the applied strain. All the descriptors for each compound in the models could be obtained from physico-chemical databases. The random forest models were used to predict the adsorption energy for hydrogen, oxygen, and hydroxyl of ≈2700 binary intermetallic compounds with stoichiometries AB, A 2 B, and A 3 B made of metallic elements, excluding those that were environmentally hazardous, radioactive, or toxic. This information was used to search for potential good catalysts for the HER and ORR from the criteria that their adsorption energy for H and O/OH, respectively, should be close to that of Pt. Further, this investigation shows that the suitably trained machine learning models can predict adsorption energies with an accuracy not far away from density functional theory calculations with minimum computational cost from descriptors that are readily available in physico-chemical databases for any compound. Moreover, the strategy presented in this paper can be easily extended to other compounds and catalytic reactions, and is expected to foster the use of ML methods in catalysis.

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

Interaction of hydrogen with actinide dioxide (011) surfaces

The corrosion and oxidation of actinide metals, leading to the formation of metal-oxide surface layers with the catalytic evolution of hydrogen, impacts the management of nuclear materials. In this work, the interaction of hydrogen with actinide dioxide (AnO 2 , An = U, Np, or Pu) (011) surfaces by Hubbard corrected density functional theory (PBEsol+U) has been studied, including spin–orbit interactions and non-collinear 3k anti-ferromagnetic behavior. The actinide dioxides crystalize in the fluorite-type structure, and although the (111) surface dominates the crystal morphology, the (011) surface energetics may lead to more significant interaction with hydrogen. The dissociative adsorption of hydrogen on the UO 2 (0.44 eV), NpO 2 (-0.47 eV), and PuO 2 (-1.71 eV) (011) surfaces has been calculated. It is found that hydrogen dissociates on the PuO 2 (011) surface; however, UO 2 (011) and NpO 2 (011) surfaces are relatively inert. Recombination of hydrogen ions is likely to occur on the UO 2 (011) and NpO 2 (011) surfaces, whereas hydroxide formation is shown to occur on the PuO 2 (011) surface, which distorts the surface structure.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Enhancing Dihydrogen Interaction of a Zirconium Metal–Organic Framework by Metal Doping

Advancing efficient hydrogen storage technologies is essential for enabling a sustainable energy future, especially in onboard applications. While hydrogen offers high gravimetric energy density and zero-emission combustion, its low volumetric energy density presents significant storage challenges. Metal-organic frameworks (MOFs), well known for their tunable porosity and high surface areas, have emerged as promising candidates for adsorption-based hydrogen storage. This study investigated a chemically robust zirconium-based MOF, MOF-808, as a representative platform for hydrogen storage enhancement through metal ion doping. Various divalent metal ions were introduced into MOF-808 via one-pot synthesis or post-synthetic modification (PSM) to evaluate their effects on metal doping efficiency, framework stability, and hydrogen adsorption performance. Our findings demonstrate that metal doping enhanced the hydrogen binding affinity of MOF-808 while preserving its structural integrity and excellent stability. A Mg-doped MOF, MOF-808@Mg 2:1, showed a 59% increase in hydrogen uptake, and a Cu-doped MOF, MOF-808-ZrCu, exhibited a 33% increase in isosteric heat of adsorption for H 2 compared to the pristine MOF-808 activated at the same temperature. This work highlights the potential of metal-functionalized stable MOFs for practical hydrogen storage applications. Furthermore, these materials are also being studied for their potential to enhance CO 2 adsorption.

Adsorption↗
DOE OSTI2021

Volumetrics of Hydrogen Storage by Physical Adsorption

Physical adsorption remains a promising method for achieving fast, reversible hydrogen storage at both ambient and cryogenic conditions. Research in this area has recently shifted to focus primarily on the volumetric (H 2 stored/delivered per volume) gains achieved within an adsorptive storage system over that of pure H 2 compression; however, the methodology for estimating a volumetric stored or delivered amount requires several assumptions related to the ultimate packing of the adsorbent material into an actual storage system volume. In this work, we critically review the different assumptions commonly employed, and thereby categorize and compare the volumetric storage and delivery across numerous different porous materials including benchmark metal-organic frameworks, porous carbons, and zeolites. In several cases, there is a significant gain in both storage and delivery by the addition of an adsorbent to the high-pressure H 2 storage system over that of pure compression, even at room temperature. Lightweight, low-density materials remain the optimal adsorbents at low temperature, while higher density, open metal-containing frameworks are necessary for high-density room temperature storage and delivery.

08 HYDROGEN↗
DOE OSTI2023

Mechanisms of adsorbing hydrogen gas on metal decorated graphene

Hydrogen is a key player in global strategies to reduce greenhouse gas emissions. In order to make hydrogen a widely used fuel, we require more efficient methods of storing it than the current standard of pressurized cylinders. An alternative method is to adsorb H 2 in a material and avoid the use of high pressures. Among many potential materials, layered materials such as graphene present a practical advantage as they are lightweight. However, graphene and other 2D materials typically bind H 2 too weakly to store it at the typical operating conditions of a hydrogen fuel cell, meaning that high pressure would still be required. Modifying the material, for example by decorating graphene with adatoms, can strengthen the adsorption energy of H 2 molecules, but the underlying mechanisms are still not well understood. In this work, we systematically screen alkali and alkaline-earth metal decorated graphene sheets for the static thermodynamic adsorption of hydrogen gas from first principles and focus on the mechanisms of binding. We show that there are three mechanisms of adsorption on metal decorated graphene and each leads to distinctly different hydrogen adsorption structures. The three mechanisms can be described as weak van der Waals physisorption, metal adatom facilitated polarization, and Kubas adsorption. Among these mechanisms, we find that Kubas adsorption is easily perturbed by an external electric field, providing a way to tune H 2 adsorption. In conclusion, this work is foundational and builds our understanding of H 2 adsorption under idealized conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Not all platinum surfaces are the same: Effect of the support on fundamental properties of platinum adlayer and its implications for the activity toward hydrogen evolution reaction

The adsorption of atomic hydrogen on a platinum monolayer supported on orthorhombic Mo 2 C(100) surface has been investigated, considering different hydrogen surface coverages. Calculations have been performed using density functional theory with the Perdew-Burke-Ernzerhof exchange correlation functional and a D3 Van der Waals corrections. The theoretical insight has been gained into atomic hydrogen interaction with Pt monolayer, supported on both molybdenum and well-studied tungsten carbide, and considering hydrogen surface coverage. Fundamental properties of Pt adlayer depend on the support, affecting hydrogen evolution activity of the resulting systems. At low hydrogen coverage all systems, with the exception of Pt supported on the molybdenum-terminated Mo 2 C, adsorb H comparably to a pristine Pt(111) surface and their high activity for the hydrogen evolution reaction is predicted. Additionally, at higher coverages supported Pt monolayers interact with atomic hydrogen unlike the Pt(111), suggesting that the activity of the supported and unsupported platinum toward hydrogen evolution reaction have different origins. Furthermore, the position of the supported platinum monolayers on the volcano curve is a function of the surface coverage, more so than for extended metal surfaces. Therefore, hydrogen surface coverage is a key variable to understand the catalytic potential, approaching towards an improved model for screening of electrocatalytic systems.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Molecular Simulations Probing the Adsorption and Diffusion of Ammonia, Nitrogen, Hydrogen, and Their Mixtures in Bulk MFI Zeolite and MFI Nanosheets at High Temperature and Pressure

Recent advances in the synthesis of MFI zeolite nanosheets have led to highly selective membranes that are promising candidates for small-scale ammonia separation from ammonia/nitrogen/hydrogen mixtures in distributed green ammonia production plants. Using force-field-based molecular simulations, we evaluate the performance of bulk all-silica MFI zeolite and a 3 nm thick all-silica MFI nanosheet for ammonia/nitrogen/hydrogen separations at moderate temperature and pressure conditions (T = 373 K, p = 5 bar) as well as conditions relevant for a membrane-based reactor–separator process (T = 523 or 623 K, p = 80 bar). Isobaric–isothermal Gibbs ensemble Monte Carlo (GEMC) simulations were carried out to understand the selective adsorption behavior for these mixtures. Molecular dynamics simulations in the canonical ensemble were performed to examine the transport behavior of ammonia in a mixture with nitrogen or hydrogen at loadings obtained from the GEMC simulations. Our results show that both bulk MFI and the nanosheet with explicit surface silanols are highly selective toward ammonia adsorption, but the adsorption selectivity decreases by factors of 4 and 10 for ammonia/nitrogen and ammonia/hydrogen mixtures as the temperature is increased from 373 to 623 K. Conversely, the diffusion selectivities toward ammonia are more favorable at process-relevant temperatures and for the MFI nanosheet. Here, at T = 523 K and p = 80 bar, our simulations predict overall separation factors of 3.8 ± 0.2 and 4.5 ± 0.3 for ammonia/nitrogen and ammonia/hydrogen mixtures, respectively, in the bulk MFI zeolite, and separation factors of 8.6 ± 0.4 and 12.5 ± 0.8, respectively, for the MFI nanosheet.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Hydrogen diffusion induced dislocation transformations in a nickel superalloy

The diffusion of hydrogen in metals and alloys induces embrittlement that can adversely affect the structural properties. We examine the adsorption and diffusion of hydrogen in Inconel-718 (IN-718), and scrutinize the ensuing effects on the dislocation behavior in the alloy to elucidate the fundamental mechanisms of hydrogen-microstructure interactions from classical molecular simulations. Hydrogen adsorption increases with time until the surface saturates, while hydrogen diffusion exhibits strong temperature dependence, with diffusion coefficients converging above 1300 K regardless of the initial hydrogen concentration in the alloy. The diffusion in IN-718 is significantly sluggish than in pure Ni, Fe, or Cr, and is strongly impacted by hydrogen concentrations, resulting in an order of magnitude higher diffusion coefficient for hydrogen (10-14 m2/s relative to 10-15 m2/s) at high concentrations, especially below 600 K. Hydrogen diffusion coefficient varies from 10-12 to 10-15 m2/s in IN-718 depending on temperature (500–1400 K). More critically, our results reveal that increasing hydrogen concentration induces microstructural changes in the alloy, transforming perfect dislocations into stair-rods and Shockley partials, with higher temperatures favoring the latter. The results are significant for hydrogen fuel applications to gain insights into the materials chemistry for designing safer and more efficient propulsion systems, particularly in high-performance environments related to controlled hydrogen combustion applications.

Banerjee, Tanumoy↗
DOE OSTI2025

Catalytic reduction of carbon dioxide to methanol over defect-laden hexagonal boron nitride: insights into reaction mechanisms

Abstract We present a density functional theory-based mechanistic understanding of CO 2 hydrogenation to value-added products on a nitrogen-vacancy (V N ) defect in hexagonal boron nitride ( dh -BN). Activation occurs through back-donation to the π * orbitals of CO 2 from the frontier orbitals (defect state) of the h- BN sheet that are localized near a nitrogen-vacancy. Subsequent hydrogenation to methanol (CH 3 OH) and formic acid (HCOOH) proceed through vacancy-facilitated co-adsorption of hydrogen and CO 2 . More importantly, our reaction pathway analyses complimented by microkinetic modeling indicate that dh -BN is potentially a low-temperature, selective catalyst for CO 2 reduction to methanol. Our findings are in agreement with experiments conducted in a mechanical reactor that show high selectivity towards methanol formation for CO 2 hydrogenation on defect induced h- BN.

Jiang, Tao (ORCID:0000000304197288)↗
DOE OSTI2020

B 2 H 6 splitting on catalytic surfaces and role of BH 3 towards hydrogen spillover

A fundamental understanding of the spillover mechanism is an open and challenging problem and plays an important role in catalysis. In particular, bond-exchange spillover mechanism is considered to be effective for reversible storage and release of hydrogen at near ambient conditions. For this, three critical steps are needed: finding the right support (acceptor), the right catalyst to split H 2 , and ensuring that once H 2 is split, the H atoms can migrate on the surface with the help of secondary catalysts and eventually hydrogenate the entire material. In this paper we address these challenges using density functional theory. Here we show that BH 3 , a secondary catalyst, can be produced by symmetrically splitting its stable precursor, B 2 H 6 , on doped metal-free surfaces such as graphene and h-BN as well as on MOF5. In addition, to reduce computational cost, we develop structural descriptor and predictive model equation to effectively screen potential BH 3 binding sites. Symmetrical splitting of B 2 H 6 on different types of materials can address the hydrogen spillover challenge, making efficient storage of hydrogen possible.

08 HYDROGEN↗
DOE OSTI2023

Outlook on texture evolution in additively manufactured stainless steels: Prospects for hydrogen embrittlement resistance, overview of mechanical, and solidification behavior

Abstract Realizing application specific manufacture with fusion-based additive manufacturing (F-BAM) processes requires understanding of the physical phenomena that drive evolution of microstructural attributes, such as texture. Current approaches for understanding texture evolution in F-BAM are majorly considerate of the phenomena occurring only during solidification. This hinders the comprehensive understanding and control of texture during F-BAM. In this perspective article, we discuss several physical phenomena occurring during and after solidification that can determine texture in F-BAM processed stainless steels (SS). A crystal plasticity-coupled hydrogen adsorption-diffusion modeling framework is also leveraged to demonstrate the prospects of grain boundary engineering with F-BAM for enhanced hydrogen embrittlement resistance of SS. Implications of varying thermokinetics in F-BAM for solidification behavior of SS are discussed. Additionally, microstructural attributes that are key to high temperature mechanical performance of SS are highlighted. Considerations as outlined in this perspective article will enable grain boundary engineering and application specific microstructural design of SS with F-BAM. Graphical abstract

36 MATERIALS SCIENCE↗
DOE OSTI2022

Phenyl‐Free Polynorbornenes for Potential Anion Exchange Ionomers for Fuel Cells and Electrolyzers

Abstract Ionomers in the catalyst layer play a critical role in the performance of fuel cells and electrolyzers. Phenyl adsorption on hydrogen oxidation catalysts and electrochemical oxidation of phenyl moieties on oxygen evolution catalysts are detrimental to the alkaline devices’ performance. Here the adsorption energy of phenyl‐containing ionomers is compared to provide the rationale for implementing phenyl‐free ionomers. Density functional theory calculations indicated that the norbornane fragment has minimal adsorption energy on Pt(111) due to the absence of aromatic π electrons. A soluble quaternized polynorbornene ionomer is prepared by vinyl addition polymerization, and it exhibits high performance in both fuel cells and electrolyzers, proving the advantage of the phenyl‐free structure. This study establishes the phenyl adsorption energy‐electrode performance relationship, highlighting the importance of material interactions between the catalysts and ionomers.

25 ENERGY STORAGE↗
DOE OSTI2023

Nuclear magnetic resonance and molecular simulation study of H 2 and CH 4 adsorption onto shale and sandstone for hydrogen geological storage

Understanding pure H 2 and H 2 /CH 4 adsorption and diffusion in earth materials is one vital step toward a successful and safe H 2 storage in depleted gas reservoirs. Despite recent research efforts such understanding is far from complete. In this work we first use Nuclear Magnetic Resonance (NMR) experiments to study the NMR response of injected H 2 into Duvernay shale and Berea sandstone samples, representing materials in confining and storage zones. Then we use molecular simulations to investigate H 2 /CH 4 competitive adsorption and diffusion in kerogen, a common component of shale. Our results indicate that in shale there are two H 2 populations, i.e., free H 2 and adsorbed H 2 , that yield very distinct NMR responses. However, only free gas presents in sandstone that yields a H 2 NMR response similar to that of bulk H 2 . About 10 % of injected H 2 can be lost due to adsorption/desorption hysteresis in shale, and no H 2 loss (no hysteresis) is observed in sandstone. Here, our molecular simulation results support our NMR results that there are two H 2 populations in nanoporous materials (kerogen). The simulation results also indicate that CH 4 outcompetes H 2 in adsorption onto kerogen, due to stronger CH 4 -kerogen interactions than H 2 -kerogen interactions. Nevertheless, in a depleted gas reservoir with low CH 4 gas pressure, about ~30 % of residual CH 4 can be desorbed upon H 2 injection. The simulation results also predict that H 2 diffusion in porous kerogen is about one order of magnitude higher than that of CH 4 and CO 2 . This work provides an understanding of H 2 /CH 4 behaviors in deleted gas reservoirs upon H 2 injection and predictions of H 2 loss and CH 4 desorption in H 2 storage.

08 HYDROGEN↗
DOE OSTI2020

Parallelized Screening of Characterized and DFT-Modeled Bimetallic Colloidal Cocatalysts for Photocatalytic Hydrogen Evolution

Using a newly designed and developed parallelized photoreactor and colorimetric detection method, a large sampling of bimetallic co-catalysts (Pd/Sn, Pd/Mo, Pd/Ru, Pd/Pb, Pd/Ni, Ni/Sn, Mo/Sn and Pt/Sn) for photocatalytic water reduction have been tested in this work. Of these co-catalysts, the combination of palladium and tin showed the highest synergistic behavior and peak hydrogen gas production at a low relative fraction of palladium. The resulting Pd/Sn bimetallic co-catalysts were characterized using high-angle annular dark-field (HAADF) and scanning transmission electron microscopy energy dispersive X-ray spectroscopy (STEM-EDS), and specifically, investigation of the palladium/tin mixture indicated that palladium and tin elements reside within the same particle. The experimental catalytic activity for the palladium/tin mixture was compared to density functional theory-derived energy values associated with the adsorption of hydrogen onto a surface. This comparison demonstrated that the typical peak found in electrochemical Sabatier volcano plots at ΔG H* = ~0 eV was replicated in the experimental photocatalytic system with a peak activity observed at ΔG H* = -0.036 eV. Computational confirmation of the results expressed here demonstrates the efficacy of colorimetric detection of hydrogen in parallel and presents a model for increasingly rapid catalyst screening.

08 HYDROGEN↗