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Using metal hydride for hydrogen storage in stationary applications and for transportation is a promising technology due to its advantages of large hydrogen storage capacity, low pressure and low energy consumption. Combining the metal hydride reactor with PCM is expected to recover the heat generated during the hydrogen absorption and use it for hydrogen desorption, thus improving the energy efficiency of the system. This paper proposes a metal hydride reactor integrated with honeycomb fins and PCM to enhance heat transfer. Based on simulations, the results show that the achieved hydrogen storage capacity is 1.326 wt%, the gravimetric and volumetric storage densities are 0.411% and 14.76 kg of H2 per m3, respectively, and the mean saturated rates are 1.222 × 10−3 g s−1 and 0.773 × 10−3 g s−1 for absorption and desorption processes. Compared with the reactor without fins, the mass and volume of the reactor using honeycomb fins are increased, resulting in a decrease in gravimetric and volumetric storage density, but a increase in reaction rate during hydrogen absorption and desorption processes. Based on this structure, we also propose a honeycomb fin reactor filled with sandwich PCM to further accelerate the heat transfer in the reaction process. Compare to the reactor with PCM only filled on the periphery of the honeycomb fins, the hydrogen absorption and desorption times are shortened by about 86.4% and 81.1%, respectively. In addition, different reactor structures are compared using multiple KPIs to provide relevant suggestions for the reactor optimization. The obtained research results can provide a reference for effective thermal management methods in MH storage systems.

A key step in creating efficient and long-lasting catalysts is understanding their deactivation mechanism(s). On this basis, the behavior of a series of Pd/corundum materials during several hydrogen adsorption/desorption cycles was studied using temperature-programmed desorption coupled with mass spectrometry and aberration-corrected transmission electron microscopy. The materials, prepared by impregnation and by sputtering, presented uniform well-dispersed Pd nanoparticles. In addition, single atoms and small clusters of Pd were only detected in the materials prepared by impregnation. Upon exposure to hydrogen, the Pd nanoparticles smaller than 2 nm and the single atoms did not present any change, while the larger ones presented a core-shell morphology, where the core was Pd and the shell was PdHx. The results suggest that the long-term activity of the materials prepared by impregnation can be attributed solely to the presence of small clusters and single atoms of Pd.

Doping of MgH2 with transition metals and their oxides is well-known procedure to improve its hydrogen (de) sorption properties, namely to lower the temperature of desorption and to achieve the kinetics speedup. In order to assess the influence Ti and TiO2 doping has on H mobility and to characterize structurally and electronically observed differences, MgH2-Mg interface doped with both Ti and TiO2 have been studied using ab-initio interface molecular dynamics and bulk calculations. Results suggest different mechanisms of MgH2 structure destabilization. The presence of dopants significantly stabilize MgH2-Mg interface, which is confirmed by work of adhesion computation. Calculated formation energies show that interface system with doped TiO2 is more stable. In terms of H mobility, molecular dynamics simulations confirm that Ti doping is more effective than TiO2 in lowering the desorption temperature. The mobility of hydrogen atoms close to dopant is much higher in the case of Ti than in the case of TiO2. Electronic structure characterization reveals that oxygen atoms with high electron affinity forms more pronounced ionic bonding with Ti and the other neighbor Mg atoms. This in turn cause a shorter Ti-H bonds in first coordination than in the case of Ti doping and further reduction of H atoms mobility. This is in accordance with molecular dynamics predictions. (C) 2016 Elsevier B.V. All rights reserved.

Doping of MgH2 with transition metals and their oxides is well-known procedure to improve its hydrogen (de) sorption properties, namely to lower the temperature of desorption and to achieve the kinetics speedup. In order to assess the influence Ti and TiO2 doping has on H mobility and to characterize structurally and electronically observed differences, MgH2-Mg interface doped with both Ti and TiO2 have been studied using ab-initio interface molecular dynamics and bulk calculations. Results suggest different mechanisms of MgH2 structure destabilization. The presence of dopants significantly stabilize MgH2-Mg interface, which is confirmed by work of adhesion computation. Calculated formation energies show that interface system with doped TiO2 is more stable. In terms of H mobility, molecular dynamics simulations confirm that Ti doping is more effective than TiO2 in lowering the desorption temperature. The mobility of hydrogen atoms close to dopant is much higher in the case of Ti than in the case of TiO2. Electronic structure characterization reveals that oxygen atoms with high electron affinity forms more pronounced ionic bonding with Ti and the other neighbor Mg atoms. This in turn cause a shorter Ti-H bonds in first coordination than in the case of Ti doping and further reduction of H atoms mobility. This is in accordance with molecular dynamics predictions. (C) 2016 Elsevier B.V. All rights reserved.

A thorough study of the structural, electronic, and hydrogen-desorption properties of - and -MgH2 phases substituted by selected transition metals (TMs) is performed through first-principles calculations based on density functional theory (DFT). The TMs considered herein include Sc, V, Fe, Co, Ni, Cu, Y, Zr, and Nb, which substitute for Mg at a doping concentration of 3.125% in both the hydrides. This insertion of TMs causes a variation in the cell volumes of - and -MgH2. The majority of the TM dopants decrease the lattice constants, with Ni resulting in the largest reduction. From the formation-energy calculations, it is predicted that except for Cu and Ni, the mixing of all the selected TM dopants with the MgH2 phases is exothermic. The selected TMs also influence the stability of both - and -MgH2 and cause destabilization by weakening the MgH bonds. Our results show that doping with certain TMs can facilitate desorption of hydrogen from - and -MgH2 at much lower temperatures than from their pure forms. The hydrogen adsorption strengths are also studied by density-of-states analysis., QC 20150918

A thorough study of the structural, electronic, and hydrogen-desorption properties of - and -MgH2 phases substituted by selected transition metals (TMs) is performed through first-principles calculations based on density functional theory (DFT). The TMs considered herein include Sc, V, Fe, Co, Ni, Cu, Y, Zr, and Nb, which substitute for Mg at a doping concentration of 3.125% in both the hydrides. This insertion of TMs causes a variation in the cell volumes of - and -MgH2. The majority of the TM dopants decrease the lattice constants, with Ni resulting in the largest reduction. From the formation-energy calculations, it is predicted that except for Cu and Ni, the mixing of all the selected TM dopants with the MgH2 phases is exothermic. The selected TMs also influence the stability of both - and -MgH2 and cause destabilization by weakening the MgH bonds. Our results show that doping with certain TMs can facilitate desorption of hydrogen from - and -MgH2 at much lower temperatures than from their pure forms. The hydrogen adsorption strengths are also studied by density-of-states analysis.

A simplified techno-economic model has been used as a screening tool to explore the factors that have the largest impact on the costs of using metal hydrides for concentrating solar thermal storage. The installed costs of a number of paired metal hydride concentrating solar thermal storage systems were assessed. These comprised of magnesium-based (MgH2, Mg 2FeH6, NaMgH3, NaMgH2F) high-temperature metal hydrides (HTMH) for solar thermal storage and Ti1.2Mn1.8H3.0 as the low-temperature metal hydride (LTMH) for hydrogen storage. A factored method approach was used for a 200 MWel power plant operating at a plant capacity factor (PCF) of 50% with 7 hours of thermal storage capacity at full-load. In addition, the hydrogen desorption properties of NaMgH2F have been measured for the first time. It has a practical hydrogen capacity of 2.5 wt% (2.95 wt% theoretical) and desorbs hydrogen in a single-step process above 478 °C and in a two-step process below 478 °C. In both cases the final decomposition products are NaMgF3, Na and Mg.Only the single-step desorption is suitable for concentrating solar thermal storage applications and has an enthalpy of 96.8 kJ mol-1 H2 at the midpoint of the hydrogen desorption plateau. The techno-economic model showed that the cost of the LTMH, Ti1.2Mn1.8H3.0, is the most significant component of the system and that its cost can be reduced by increasing the operating temperature and enthalpy of hydrogen absorption in the HTMH that, in turn, reduces the quantity of hydrogen required in the system for an equivalent electrical output. The result is that, despite the fact that the theoretical thermal storage capacity of NaMgH2F (1416 kJ kg -1) is substantially lower than the theoretical values for MgH 2 (2814 kJ kg-1), Mg2FeH6 (2090 kJ kg-1) and NaMgH3 (1721 kJ kg-1), its higher enthalpy and operating temperature leads to the lowest installed cost of the systems considered. A further decrease in cost could be achieved by utilizing metal hydrides wi

This study deals with the investigations of structural, electronic and thermodynamic properties of MgH2 doped with selected transition metals (TMs) by means of hybrid density functional theory (PBE0). On the structural side, the calculated lattice parameters and equilibrium volumes increase in case of Sc, Zr and Y opposite to all the other dopants indicating volumetrically increased hydrogen density. Except Fe, all the dopants improve the kinetics of MgH2 by reducing the heat of adsorption with Cu, Nb, Ni and V proving more efficient than others studied TM's. The electronic properties have been studied by density of states and correlated with hydrogen adsorption energies., QC 20131210

The behavior of gaseous foreign species (e.g., helium and hydrogen), which are either generated, adsorbed or implanted within the structural materials (e.g., iron and zirconium) exposed to irradiation environments, is an important and largely unsolved topic, as they intensively interact with the irradiation-induced defects, or bond with the lattice atoms to form new compounds, and impose significant effects on their microstructural and mechanical properties in fission and fusion reactors. This research investigates two cases of gas diffusion in metals (i.e., the helium-point defect interactions in iron and kinetics of hydrogen desorption from zirconium hydride) through extensive experimental and modeling studies, with the objective of improving the understanding of helium effects on the microstructures of iron under irradiation and demonstrating the kinetics of hydrogen diffusion and precipitation behavior in zirconium that are crucial to predict cladding failures and hydride fuel performance.The study of helium effects in structural materials aims to develop a self-consistent, experimentally validated model of helium - point defect, defect cluster and intrinsic defects through detailed inter-comparisons between experimental measurements on helium ion implanted iron single crystals and computational models. The combination of thermal helium desorption spectrometry (THDS) experiment with the cluster dynamic model helps to reveal the influence of impurities on the energetics and kinetics of the He-defect interactions and to realize the identification of possible mechanisms governing helium desorption peaks. Positron annihilation spectroscopy is employed to acquire additional information on He-vacancy cluster evolution, which provides an opportunity to validate the model qualitatively. The inclusion of He - self-interstitial clusters extends the cluster dynamic model while MD simulations explore the effects of dislocation loops on helium clustering. In addition, the in

The behavior of gaseous foreign species (e.g., helium and hydrogen), which are either generated, adsorbed or implanted within the structural materials (e.g., iron and zirconium) exposed to irradiation environments, is an important and largely unsolved topic, as they intensively interact with the irradiation-induced defects, or bond with the lattice atoms to form new compounds, and impose significant effects on their microstructural and mechanical properties in fission and fusion reactors. This research investigates two cases of gas diffusion in metals (i.e., the helium-point defect interactions in iron and kinetics of hydrogen desorption from zirconium hydride) through extensive experimental and modeling studies, with the objective of improving the understanding of helium effects on the microstructures of iron under irradiation and demonstrating the kinetics of hydrogen diffusion and precipitation behavior in zirconium that are crucial to predict cladding failures and hydride fuel performance.The study of helium effects in structural materials aims to develop a self-consistent, experimentally validated model of helium - point defect, defect cluster and intrinsic defects through detailed inter-comparisons between experimental measurements on helium ion implanted iron single crystals and computational models. The combination of thermal helium desorption spectrometry (THDS) experiment with the cluster dynamic model helps to reveal the influence of impurities on the energetics and kinetics of the He-defect interactions and to realize the identification of possible mechanisms governing helium desorption peaks. Positron annihilation spectroscopy is employed to acquire additional information on He-vacancy cluster evolution, which provides an opportunity to validate the model qualitatively. The inclusion of He - self-interstitial clusters extends the cluster dynamic model while MD simulations explore the effects of dislocation loops on helium clustering. In addition, the in

The crystal structures of hydrogenated and unhydrogenated Sc(Al 1-xNi x) 2 Laves phases have been studied by combining several diffraction techniques and it is shown that hydrogen is situated interstitially in the A 2B 2-sites, which have the maximum number of scandium neighbours. The hydrogen absorption/desorption behaviour has also been investigated. It is shown that a solid solution of hydrogen forms in the mother compound. The hydrogen storage capacity exceeds 1.7 H/f.u. at 374 K, and the activation energy of hydrogen desorption was determined to 4.6 kJ/mol H 2. It is shown that these compounds share the same local coordination as Frank-Kasper-type approximants and quasicrystals, which opens up the possibility of finding many new hydride phases with these types of crystal structures.

Glassy carbon was irradiated with 15 key H(+) ion beam. It was observed that the implanted hydrogen is unstable in material and evolves as H, H(2) and H(2)O. Post-irradiation evolution of H, H(2) and H(2)O from proton irradiated glassy carbon was monitored by temperature programmed desorption (TPD) in the period of 30 days. In between irradiation and TPD measurements the irradiated samples were stored in air. The evolution of the molecular hydrogen, although the protons are implanted deeply below the surface of the disordered glassy carbon, proceeds over the same mechanism as in the case of low-energy H-atoms chemisorbed on the very surface of an ideal graphite structure. (C) 2011 Elsevier B.V. All rights reserved.

Glassy carbon was irradiated with 15 key H(+) ion beam. It was observed that the implanted hydrogen is unstable in material and evolves as H, H(2) and H(2)O. Post-irradiation evolution of H, H(2) and H(2)O from proton irradiated glassy carbon was monitored by temperature programmed desorption (TPD) in the period of 30 days. In between irradiation and TPD measurements the irradiated samples were stored in air. The evolution of the molecular hydrogen, although the protons are implanted deeply below the surface of the disordered glassy carbon, proceeds over the same mechanism as in the case of low-energy H-atoms chemisorbed on the very surface of an ideal graphite structure. (C) 2011 Elsevier B.V. All rights reserved.

Glassy carbon was irradiated with 15 key H(+) ion beam. It was observed that the implanted hydrogen is unstable in material and evolves as H, H(2) and H(2)O. Post-irradiation evolution of H, H(2) and H(2)O from proton irradiated glassy carbon was monitored by temperature programmed desorption (TPD) in the period of 30 days. In between irradiation and TPD measurements the irradiated samples were stored in air. The evolution of the molecular hydrogen, although the protons are implanted deeply below the surface of the disordered glassy carbon, proceeds over the same mechanism as in the case of low-energy H-atoms chemisorbed on the very surface of an ideal graphite structure. (C) 2011 Elsevier B.V. All rights reserved.

LiBH4 hydrogen desorption is strongly improved by its confinement to the nanoscale into a mesoporous carbon, prepared by the template method, having a pore diameter near 4 nm and a porous volume of 1.1 cm3 g-1. The LiBH4/carbon composites are prepared by room temperature impregnations of the carbon matrix with LiBH4 solubilized within ethers. LiBH4/carbon composites with a 33:67 weight ratio show excellent desorption kinetics with a hydrogen release of 3.4 wt.% in 90 min at 300 °C, whereas the decomposition of neat LiBH4 is not significant at the same temperature. Moreover, both Differential Scanning Calorimetry and Thermal Desorption Spectroscopy experiments show that the hydrogen release for the 33:67 LiBH4/carbon composite occurs in one single step immediately above the LiBH4 melting temperature (280 °C) without any formation of intermediate compounds (like dodecaborane) as encountered with neat LiBH4. Such modification of the hydrogen release mechanism path was never reported for confined LiBH4 nanoparticles. Last the presence of the carbonaceous matrix is expected to be largely beneficial for handling the heat transfer associated with the endothermic character of the LiBH4 decomposition process. © 2009 Elsevier B.V. All rights reserved.

LiBH4 hydrogen desorption is strongly improved by its confinement to the nanoscale into a mesoporous carbon, prepared by the template method, having a pore diameter near 4 nm and a porous volume of 1.1 cm3 g-1. The LiBH4/carbon composites are prepared by room temperature impregnations of the carbon matrix with LiBH4 solubilized within ethers. LiBH4/carbon composites with a 33:67 weight ratio show excellent desorption kinetics with a hydrogen release of 3.4 wt.% in 90 min at 300 °C, whereas the decomposition of neat LiBH4 is not significant at the same temperature. Moreover, both Differential Scanning Calorimetry and Thermal Desorption Spectroscopy experiments show that the hydrogen release for the 33:67 LiBH4/carbon composite occurs in one single step immediately above the LiBH4 melting temperature (280 °C) without any formation of intermediate compounds (like dodecaborane) as encountered with neat LiBH4. Such modification of the hydrogen release mechanism path was never reported for confined LiBH4 nanoparticles. Last the presence of the carbonaceous matrix is expected to be largely beneficial for handling the heat transfer associated with the endothermic character of the LiBH4 decomposition process. © 2009 Elsevier B.V. All rights reserved.

LiBH4 hydrogen desorption is strongly improved by its confinement to the nanoscale into a mesoporous carbon, prepared by the template method, having a pore diameter near 4 nm and a porous volume of 1.1 cm3 g-1. The LiBH4/carbon composites are prepared by room temperature impregnations of the carbon matrix with LiBH4 solubilized within ethers. LiBH4/carbon composites with a 33:67 weight ratio show excellent desorption kinetics with a hydrogen release of 3.4 wt.% in 90 min at 300 °C, whereas the decomposition of neat LiBH4 is not significant at the same temperature. Moreover, both Differential Scanning Calorimetry and Thermal Desorption Spectroscopy experiments show that the hydrogen release for the 33:67 LiBH4/carbon composite occurs in one single step immediately above the LiBH4 melting temperature (280 °C) without any formation of intermediate compounds (like dodecaborane) as encountered with neat LiBH4. Such modification of the hydrogen release mechanism path was never reported for confined LiBH4 nanoparticles. Last the presence of the carbonaceous matrix is expected to be largely beneficial for handling the heat transfer associated with the endothermic character of the LiBH4 decomposition process. © 2009 Elsevier B.V. All rights reserved.

The current study focuses on the hydrogen desorption properties of hydrogenated Mg24Y5. Recently, we have reported the formation of unidirectional MgH2 structures by hydrogen absorption and induced disproportionation of Mg24Y5. During hydrogen desorption, a complex voiding phenomenon produces Mg tubes and carved particles with nano-sized walls. The selected area electron diffraction patterns demonstrate that the Mg tubes are single crystals. A harmonized picture of the unidirectional growth based on different Mg vapor models is proposed. The kinetic properties of hydrogen desorption are improved as compared with commercial MgH2. Hydrogenation/dehydrogenation cycling lowers the thermal stability of the hydrogen desorption at the expense of the total desorbed hydrogen capacity. Both whiskers and microparticles are depleted into clusters of nanoparticles after extensive cyclin

The low index Magnesium hydride surfaces, MgH2(0 0 1) and MgH2(1 1 0), have been studied by ab intio Density Functional Theory (DFT) calculations. It was found that the MgH2(1 1 0) surface is more stable than MgH2(0 0 1) surface, which is in good agreement with the experimental observation. The H2 desorption barriers vary depending on the crystalline surfaces that are exposed and also the specific H atom sites involved – they are found to be generally high, due to the thermodynamic stability of the MgH2 system, and are larger for the MgH2(0 0 1) surface. The pathway for recombinative desorption of one in-plane and one bridging H atom from the MgH2(1 1 0) surface was found to be the lowest energy barrier amongst those computed (172 KJ/mol) and is in good agreement with the experimental estimates.

Dynamical calculations are reported for D-2 dissociative chemisorption on and associative desorption from a Si(100) surface. These calculations use the dynamically relevant effective potential which is based on an ab initio potential energy surface for the ''pre-paired'' species. Three coordinates are included dynamically; the distance to the surface, the D-D bond length and a Si phonon coordinate. Other coordinates (multidimensionality) have been included via a static approximation. Both an asymmetric and symmetric reaction paths are considered. While energetics favors the asymmetric path, phase space favors the symmetric one. Under the conditions of many experiments, either could dominate. The calculations show quite weak dynamic coupling to the Si lattice for both paths, i.e., weak surface temperature dependences to dissociation and small energy loss to the lattice upon desorption. These calculations do not support previous suggestions that either a strong coupling to the lattice or ''entropic'' effects can reconcile the apparent violation of detailed balance obtained by comparing experimental dissociation to desorption barriers. In fact, the results reported here do not agree with several experimental findings. We discuss several possibilities for this disagreement, including experimental artifact, limitations in the dynamical model and even the possibility that electronically adiabatic dynamics involving the ''pre-paired'' species is not relevant to experiments on real systems. (C) 1996 American Institute of Physics.

The energetics of H2 interacting with the Si(100) surface is studied by means of ab initio total-energy calculations within the framework of density-functional theory. We find a direct desorption pathway from the monohydride phase that is compatible with experimental activation energies and demonstrate the importance of substrate relaxation for this process. Both the transition state configuration and the barrier height depend crucially on the degree of buckling of the Si dimers on the Si(100) surface. The adsorption barrier height on the clean surface is governed by the buckling via its influence on the surface electronic structure. We discuss the consequences of this coupling for adsorption experiments and the relation between adsorption and desorption.

With their high capacity, light-metal hydrides – like MgH2 – remain under scrutiny as reversible H-storage materials. A key question persists: Is there a means to enhance the hydrogen desorption/adsorption properties of this “simple” hydride by decreasing size (e.g., creating nano-sized particles by ball-milling) and/or adding catalyst dopants? Thus, we need to determine accurately both the enthalpy and kinetic barriers controlling desorption, but for realistic, defected cases. Employing density functional theory (DFT) and simulated annealing, we studied initial H2 desorption from nanoclusters and semi-infinite stepped surfaces with and without transition-metal “catalyst” dopants (Ti or Fe). The large 450-atom supercell of the (110)x(1 ̅10) single stepped terrace permits the study of the effects of catalytic dopant with 10 unique dopant sites at step edges, kinks sites, and terrace sites. Extensive DFT-based simulated annealing studies were performed to find the dopants site preference and mechanism for catalyst-enhanced release of hydrogen, with additional detailed understanding from the spin-polarized electronic-structure (density of states) and charge densities. Different kink environments at the stable (110)x(1 ̅10) interface were explored to model the stability of diffusion of H to the dopant before desorption. For the most stable initial and final (possibly magnetic) states, extensive Nudged Elastic Band (NEB) calculations were performed to explore the potential energy surface (desorption enthalpies and kinetic barriers). A moment transition NEB calculation was created whereby each image was initialized to its most stable magnetic state and then images along the transition path were allowed to relax according to the NEB algorithm. This approach provided the lowest energy activation states. Together the DFT-based simulated annealing and NEB simulations determined the enthalpy change and transition-state (kinetic barrier) for desorption (H2 release to vacuum). A

The kinetics of the desorption of firmly adsorbed hydrogen from the surface of massive foamed nickel was studied over a temperature range of 453 to 753 K. The effects of plasmochemical (in oxygen and hydrogen plasmas) and thermal (annealing and quenching) treatments on the kinetic characteristic of hydrogen desorption were examined. It was found that the values of the activation energy and preexponential factor of the desorption rate constant differ for the temperature ranges below and above the Curie and Curie-Weiss points. It was discovered that the treatment of foamed nickel samples in the plasma of a hydrogen high-frequency discharge produced a more significant effect on the characteristics of hydrogen desorption than the treatment in the plasma of an oxygen glow discharge. Thermal treatments of the samples also affect the characteristics of hydrogen desorption. The experimental results were explained by changes in the magnetization of Ni, which, according to the theory of s-d-electron exchange interaction, affects the electron work function, and by the formation of additional point defects at the surface and in the subsurface layer of the metal during plasma treatment. Copyright © 2005 by Pleiades Publishing, Inc.