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Evaluation of hydrogen sorption and permeation parameters in liquid metal membranes via Sieverts' apparatus
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Structural study of Ni- or Mg-based complexes incorporated within UiO-66-NH{sub 2} framework and their impact on hydrogen sorption properties
Nickel and magnesium acetylacetonate molecular complexes were post-synthetically incorporated into microporous zirconium-based MOF (UiO-66-NH{sub 2}) in order to introduce active open-metal sites for hydrogen sorption. Elemental analysis, nitrogen physisorption and DFT calculations revealed that 5 molecules of Ni(acac){sub 2} or 2 molecules of Mg(acac){sub 2} were incorporated into one unit cell of UiO-66-NH{sub 2}. {sup 1}H–{sup 13}C CPMAS and {sup 1}H MAS NMR spectroscopy showed that, although embedded within the pores, both Ni- and Mg-complexes interacted with the UiO-66-NH{sub 2} framework only through weak van der Waals bonds. Inclusion of metal complexes led to the decrease of hydrogen sorption capacities in Ni-modified as well as in Mg-modified samples in comparison with the parent UiO-66-NH{sub 2}. The isosteric hydrogen adsorption enthalpy slightly increased in the case of Ni-modified material, but not in the case of Mg-modified analogue. - Graphical abstract: A post-synthesis impregnation of Mg- and Ni-acetylacetonate complexes performed on zirconium-based MOF UiO-66-NH{sub 2} does influence the hydrogen sorption performance with respect to the parent matrix. The structural study revealed that Mg- and Ni-acetylacetonate molecules interact with zirconium-terephthalate framework only by weak interactions and they are not covalently bonded to aminoterephthalate ligand. Still, they remain confined into the pores even after hydrogen sorption experiments. - Highlights: • Mg- and Ni-acetylacetonate molecules embedded in the pores of UiO-66-NH{sub 2} by PSM. • Molecules of complexes interact with framework only by van der Waals interactions. • Type/structure of deposited metal-complex impact hydrogen enthalpy of adsorption.
Hydrogen sorption in titanium alloys with a symmetric {Sigma}5(310) tilt grain boundary and a (310) surface
The hydrogen sorption in intermetallic B2 TiM (M = Ni, Co, Pd) with a symmetric {Sigma}5(310) tilt grain boundary and a (310) surface is studied by density functional theory methods. The effect of hydrogen on the electronic characteristics of the alloys is analyzed as a function of a sorption position at the interfaces. The hydrogen sorption energy is shown to depend on the local environment of hydrogen; on the whole, hydrogen at the interfaces prefers titanium-rich positions. The hydrogen sorption energy in metal-rich positions decreases when the d shell of the second alloy component is filled with electrons. The grain-boundary energy, the surface energy, and the hydrogen segregation energies to the interfaces are calculated. Hydrogen sorption in titanium alloys is shown to decrease Griffith work and to favor brittle fracture along tilt grain boundaries.
Initial test performance of a closed-cycle continuous hydrogen sorption cooler, the Planck sorption breadboard cooler
JPL is developing a continuous hydrogen sorption cryocooler for the ESA Planck mission, which will measure the anisotropy in the cosmic microwave background.
Cryogenic system design for a hydrogen sorption cooler
This paper presents the cryogenic design of Hydrogen Sorption Cooler, part of cryogenic chain in the Planck Mission (ESA).
Structural, Electrochemical and Hydrogen Sorption Studies of Nanocrystalline Ti-V-Co and Ti-V-Ni-Co Alloys Synthesized by Mechanical Alloying Method
In this paper, Ti-V-Co and Ti-V-Ni-Co alloys are considered as the hydrogen storage systems and the negative electrodes in Ni-MH{sub x} secondary batteries. This work shows results of studies that have been made on Ti{sub 0.5}V{sub 1.5−x}Co{sub x} and Ti{sub 0.5}V{sub 1.4−x}Ni{sub 0.1}Co{sub x} nanocrystalline alloys (x = 0, 0.1 0.2, 0.3) synthesized by the mechanical alloying technique. The goal of this study is to determine an effect of partial replacement of V by Co atoms on hydrogen storage and electrochemical properties of Ti-V and Ti-V-Ni alloys. X-ray diffraction studies have proven that 14 h of the ball milling has resulted in crystallization of body-centered-cubic solid solution. Studies performed on high-resolution transmission electron microscope confirm creation of nanocrystalline materials. Hydrogen sorption/desorption measurements that have been performed at 303 K show that Co accelerates the hydrogen sorption process, diminishes hysteresis and ameliorates the hydrogen storage reversibility. Properties of Ti-V-Co alloys, described in this work, originate mainly from structure of these materials. Electrochemical measurements of Ti-V-Co alloys have shown these materials poorly absorb hydrogen in 6 M KOH solution. Ti{sub 0.5}V{sub 1.4−x}Ni{sub 0.1}Co{sub x} alloys are characterized by better activation properties and improved cyclability in comparison to Co-free Ti{sub 0.5}V{sub 1.4}Ni{sub 0.1} alloy.
Hydrogen sorption characteristics of nanostructured Pd–10Rh processed by cryomilling
Palladium and its alloys are model systems for studying solid-state storage of hydrogen. Mechanical milling is commonly used to process complex powder systems for solid-state hydrogen storage; however, milling can also be used to evolve nanostructured powder to modify hydrogen sorption characteristics. In the present study, cryomilling (mechanical attrition milling in a cryogenic liquid) is used to produce nanostructured palladium-rhodium alloy powder. Characterization of the cryomilled Pd-10Rh using electron microscopy, X-ray diffraction, and surface area analysis reveals that (i) particle morphology evolves from spherical to flattened disk-like particles; while the (ii) crystallite size decreases from several microns to less than 100 nm and (iii) dislocation density increases with increased cryomilling time. Hydrogen absorption and desorption isotherms as well as the time scales for absorption were measured for cryomilled Pd-10Rh, and correlated with observed microstructural changes induced by the cryomilling process. In short, as the microstructure of the Pd-10Rh alloy is refined by cryomilling: (i) the maximum hydrogen concentration in the α-phase increases, (ii) the pressure plateau becomes flatter, and (iii) the equilibrium hydrogen capacity at 760 Torr increases. In addition, the rate of hydrogen absorption was reduced by an order of magnitude compared to non-cryomilled (atomized) powder.
Optimization of Nano-Carbon Materials for Hydrogen Sorption
Research undertaken has added to the understanding of several critical areas, by providing both negative answers (and therefore eliminating expensive further studies of unfeasible paths) and positive feasible options for storage. Theoretical evaluation of the early hypothesis of storage on pure carbon single wall nanotubes (SWNT) has been scrutinized with the use of comprehensive computational methods (and experimental tests by the Center partners), and demonstrated that the fundamentally weak binding energy of hydrogen is not sufficiently enhanced by the SWNT curvature or even defects, which renders carbon nanotubes not practical media. More promising direction taken was towards 3-dimensional architectures of high porosity where concurrent attraction of H2 molecule to surrounding walls of nano-scale cavities can double or even triple the binding energy and therefore make hydrogen storage feasible even at ambient or somewhat lower temperatures. An efficient computational tool has been developed for the rapid capacity assessment combining (i) carbon-foam structure generation, (ii) accurate empirical force fields, with quantum corrections for the lightweight H2, and (iii) grand canonical Monte Carlo simulation. This made it possible to suggest optimal designs for carbon nanofoams, obtainable via welding techniques from SWNT or by growth on template-zeolites. As a precursor for 3D-foams, we have investigated experimentally the synthesis of VANTA (Vertically Aligned NanoTube Arrays). This can be used for producing nano-foams. On the other hand, fluorination of VANTA did not show promising increase of hydrogen sorption in several tests and may require further investigation and improvements. Another significant result of this project was in developing a fundamental understanding of the elements of hydrogen spillover mechanisms. The benefit of developed models is the ability to foresee possible directions for further improvement of the spillover mechanism.
Recent Progress in Development of Hydrogen Sorption Cryocoolers for Space Applications
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In-situ Spectroscopic Identification of Hydrogen Binding Sites on Carbon-Based Hydrogen Sorption Materials
Abstract not provided
DOE Hydrogen Sorption Center of Excellence: Synthesis and Processing of Single-Walled Carbon Nanohorns for Hydrogen Storage and Catalyst Supports
The objective of the project was to exploit the unique morphology, tunable porosity and excellent metal supportability of single-walled carbon nanohorns (SWNHs) to optimize hydrogen uptake and binding energy through an understanding of metal-carbon interactions and nanoscale confinement. SWNHs provided a unique material to understand these effects because they are carbon nanomaterials which are synthesized from the 'bottom-up' with well-defined, sub-nm pores and consist of single-layer graphene, rolled up into closed, conical, horn-shaped units which form ball-shaped aggregates of {approx}100-nm diameter. SWNHs were synthesized without metal catalysts by the high-temperature vaporization of solid carbon, so they can be used to explore metal-free hydrogen storage. However, SWNHs can also be decorated with metal nanoparticles or coatings in post-processing treatments to understand how metals augment hydrogen storage. The project first explored how the synthesis and processing of SWNHs could be modified to tailor pore sizes to optimal size ranges. Nanohorns were rapidly synthesized at 20g/hr rates by high-power laser vaporization enabling studies such as neutron scattering with gram quantities. Diagnostics of the synthesis process including high-speed videography, fast pyrometry of the graphite target, and differential mobility analysis monitoring of particle size distributions were applied in this project to provide in situ process control of SWNH morphology, and to understand the conditions for different pore sizes. We conclude that the high-temperature carbon-vaporization process to synthesize SWNHs is scalable, and can be performed by electric arc or other similar techniques as economically as carbon can be vaporized. However, the laser vaporization approach was utilized in this project to permit the precise tuning of the synthesis process through adjustment of the laser pulse width and repetition rate. A result of this processing control in the project was to eliminate the large (2-3 nm) internal pores of typical SWNHs which were found not to store hydrogen effectively. Post processing treatments of the as-synthesized SWNHs focused on pore size, surface area, and metal decoration in order to understand the effects of each on measured hydrogen uptake. Wet chemistry and gas-phase oxidation treatments were developed throughout the life of the project to adjust the interstitial and slit pore sizes of the as-produced SWNHs, and increase the surface area to a maximum value of 2200 m2/g. In addition, wet chemistry approaches were used to develop methods to decorate the nanohorns with small Pt and Pd nanoparticles for metal-assisted hydrogen storage. Finally, oxygen-free decoration of SWNHs with alkaline earth metals (Ca) was developed using pulsed laser deposition and vacuum evaporation in order to produce surface coatings with high static electric fields sufficient to polarize and bind dihydrogen. Decoration of SWNHs with Pt and Pd nanoparticles resulted in enhanced binding energy (NREL, 36 kJ/mol), as well as enhancement in the room temperature uptake of 0.6 wt.% (for undecorated, oxidized, pure-C SWNHs at 20 bar), to 1.6 wt% for Pt- and Pd-decorated SWNHs at 100 bar, comparable to MOF-177 materials. NIST neutron scattering on gram quantity Pt- and Pd-decorated SWNHs showed clear evidence for 'spillover' type losses of molecular hydrogen and determined the onset temperature for this effect to be between 150K < T < 298K.High (2142 m2/g) surface area SWNH materials with variable pore sizes and metal-decorated SWNHs were demonstrated with metals (Pt, Pd) resulting in increased excess storage (3.5 wt. % at 77K). Compression results in bulk SWNH samples with density 1.03 g/cm3, and 30 g/L volumetric capacity. In summary, SWNHs were found to be unique carbon nanomaterials which can be produced continuously at high rates from vaporization of pure carbon. Their inherent pore structure exhibits significant room temperature hydrogen storage in sub-nm pores, and their morphology serves as an excellent metal catalyst support for small (2-3 nm nanoparticles). Pt- and Pd-nanoparticle-decorated SWNHs exhibit clear evidence for metal-assisted hydrogen storage which is activated at T>150 K, permitting additional room-temperature storage up to 1.8 wt.% at 100 bar. One of the key results of the project were theoretical predictions for doped, decorated, and filled nanostructures with distributed charge to maintain high static electric fields sufficient to polarize and bind hydrogen. This concept indicates a promising new direction for hydrogen storage materials.
Effects and Mechanisms of Mechanical Activation on Hydrogen Sorption/ Desorption of Nanoscale Lithium Nitrides
The objective of this project is to investigate and develop novel, mechanically activated, nanoscale Li 3 N-based and LiBH 4 -based materials that are able to store and release ~10 wt% hydrogen at temperatures near 100°C with a plateau hydrogen pressure of less than 10 bar. Four (4) material systems have been investigated in the course of this project in order to achieve the project objective. These 4 systems are (i) LiNH 2 +LiH, (ii) LiNH 2 +MgH 2 , (iii) LiBH 4 , and (iv) LiBH 4 +MgH 2 .
IImprove hydrogen sorption kinetics of MgH2 by doping carbon-encapsulated iron-nickel nanoparticles
Magnesium hydride (MgH2) with excellent hydrogen storage kinetics is important for the wide application of hydrogen energy. Herein, to accelerate the sorption kinetics of MgH2 and lower its dehydrogenation temperature, we design and prepare a carbon film coated dual transition metal alloy, the Fe0.64Ni0.36@C composite with a coreshell structure, and employ it as an additive to synthesize MgH2–Fe0.64Ni0.36@C system by ball-milling and hydriding combustion method. In contrast to pure MgH2, the initial hydrogen release temperature of the MgH2–Fe0.64Ni0.36@C composite lowers to 250°C from 480°C and the composite can absorb 5.18 wt% H2 within 20 min (150°C, 3 MPa H2). More importantly, the apparent activation energy of the dehydrogenation for decomposition of Fe0.64Ni0.36@C-doped MgH2 reduced from 162.8 ± 8.3 kJ/mol to 86.9 ± 4.6 kJ/mol. It is believed that the Fe@C and Mg2Ni/Mg2NiH4 formed on the surface of Mg/MgH2 act as intermediates of electron transfer between Mg2+ and H–, which synergistically enhanced the hydrogen absorption and desorption kinetics properties of the MgH2. Moreover, the MgH2 co-doped with the multiple in-situ formed active particles shows excellent cycling performance, indicative of potential application in practical hydrogen storage in the near future.
Cryogenic system design for a hydrogen sorption cooler
For several future space applications, long life vibration free collers are needed to cover the temperature range from 60K to about 4K. We describe the development of a novel cryogenic system capable of reaching 18K in coupled resevoirs that provide distributed cooling with small temperature fluctuations.
Fluorinated Covalent Organic Frameworks: A Novel Pathway to Enhance Hydrogen Sorption and Control Isosteric Heats of Adsorption; HyMARC Seed Project Final Report
Organic framework materials, as a unique sub-class of carbon-based sorbents, have gained increasing attention for promising attributes toward gas storage. Calculations of the hydrogen capacity of optimized frameworks show potential to achieve greater than 60 g/L storage of hydrogen, placing metal-organic frameworks (MOFs) and COFs near the top of the class of porous materials. However, at the ensemble level, poor stacking creates a quasi-amorphous material with low structural integrity and low effective surface area. The chemical versatility of COFs allows for additional methods for producing long-range order that specifically target the inter-layer interactions in COFs but that leave key pore-accessible linker sites open. These modifications (either during synthesis or post-synthetic) enable a host of strategies to both improve crystalline order for more stable and higher surface, as well as add metals with open coordination for enhanced H 2 binding enthalpy.
Hydrogen Sorption Kinetics on Bare and Platinum-Modified Palladium Nanofilms, Grown by Electrochemical Atomic Layer Deposition (E-ALD)
Nanofilms of Pd were grown using an electrochemical form of atomic layer deposition (E-ALD) on 100 nm evaporated Au films on glass. Multiple cycles of surface-limited redox replacement (SLRR) were used to grow deposits. Each SLRR involved the underpotential deposition (UPD) of a Cu atomic layer, followed by open circuit replacement via redox exchange with tetrachloropalladate, forming a Pd atomic layer: one E-ALD deposition cycle. That cycle was repeated in order to grow deposits of a desired thickness. 5 cycles of Pd deposition were performed on the Au on glass substrates, resulting in the formation of 2.5 monolayers of Pd. Those Pd films were then modified with varying coverages of Pt, also formed using SLRR. The amount of Pt was controlled by changing the potential for Cu UPD, and by increasing the number of Pt deposition cycles. Hydrogen absorption was studied using coulometry and cyclic voltammetry in 0.1 M H 2 SO 4 as a function of Pt coverage. The presence of even a small fraction of a Pt monolayer dramatically increased the rate of hydrogen desorption. However, this did not reduce the films’ hydrogen storage capacity. The increase in desorption rate in the presence of Pt was over an order of magnitude.