Layer-resolved study of the Mg to MgH2 transformation in Mg–Ti films with short-range chemical order

Eijt, S.W.H.; Leegwater, H.; Schüt, H.; Anastasopol, A.; Egger, Werner; Ravelli, L.; Hugenschmidt, C.; Dam, B.

doi:10.1016/j.jallcom.2010.09.157

Cited by 12 publications

(20 citation statements)

References 16 publications

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“…39 The detailed procedures for the The Journal of Physical Chemistry C Article positron Doppler broadening depth profiling method were described in the previous report. 40,41 Hydrogenation and Dehydrogenation Properties. Hydrogenation properties of the gradient thin film on 70 × 5 × 0.5 mm substrate were measured with hydrogenography.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

Destabilization of Mg Hydride by Self-Organized Nanoclusters in the Immiscible Mg–Ti System

et al. 2015

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Mg is an attractive hydrogen storage material not only because of its high gravimetric and volumetric hydrogen capacities but also because of it low material costs. However, the hydride of MgH 2 is too stable to release hydrogen under moderate conditions. We demonstrate that the formation of nanometer-sized clusters of Mg reduces the stability of MgH 2 by the interface energy effect in the immiscible Mg−Ti system. Ti-rich Mg x Ti 1−x (x < 0.5) thin films deposited by magnetron sputtering have a hexagonal close packed (HCP) structure, which forms a face-centered cubic (FCC) hydride phase upon hydrogenation. Positron Doppler broadening depth profiling demonstrates that after hydrogenation, nanometer-sized MgH 2 clusters are formed which are coherently embedded in an FCC TiH 2 matrix. The P (pressure)−T (optical transmission) isotherms measured by hydrogenography show that these MgH 2 clusters are destabilized. This indicates that the formation of nanometer-sized Mg allows for the development of a lightweight and cheap hydrogen storage material with a lower desorption temperature. ■ INTRODUCTIONMg is one of the typical lightweight metals with a density of 1.74 g cm −3 , which is much less than that of many transition and rare earth metals. 1 Mg has a hexagonal close-packed (HCP) structure, and that forms the hydride phase MgH 2 by hydrogenation. MgH 2 has a rutile-type body-centered tetragonal (BCT) structure (α-MgH 2 ) at moderate temperatures and pressures. 2,3 The gravimetric hydrogen capacity is 7.6 mass %, which is higher than most metal hydrides. The volumetric hydrogen capacity of 109 g-H 2 l −1 corresponds to 2.9 times the gaseous hydrogen concentration under a pressure of 70 MPa and 1.6 times the one of liquid hydrogen at 20 K. 4 Mg is one of the most attractive hydrogen storage materials not only because of the high capacity but also the low material costs. However, MgH 2 is too stable to desorb hydrogen at moderate temperatures and pressures and thus unsuited for practical applications. The enthalpy for hydride formation is −75 kJ mol −1 -H 2 , 2,3 which corresponds to a dehydrogenation temperature of around 550 K under a hydrogen pressure of 0.1 MPa. Furthermore, the slow reaction kinetics for hydrogenation and dehydrogenation is a disadvantage for using it as hydrogen storage material. The diffusion of hydrogen in both Mg and MgH 2 has been studied, 2,5,6 and the activation energy for hydrogen diffusion in MgH 2 of 140 kJ mol −1 is particularly high. 6 This value is around 2−5 times those in hydrides of LaNi 5 7 and V. 8 A possible way to destabilize MgH 2 and enhance the reaction kinetics is to reduce the size of Mg. It has been calculated that MgH 2 is destabilized by decreasing the size on a nanometer scale. 9−11 The destabilization is remarkable for a MgH 2 cluster with a diameter below 1.3 nm, corresponding to 19 Mg atoms or less. 11 On the basis of these calculations, the dehydrogenation temperature for a MgH 2 cluster of 0.9 nm would be more than 100 K lower than for bulk MgH 2 under a given hydr...

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Section: ■ Experimental Sectionmentioning

confidence: 99%

Destabilization of Mg Hydride by Self-Organized Nanoclusters in the Immiscible Mg–Ti System

et al. 2015

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“…The presence of a chemically partially segregated but structurally coherent metastable phase in Mg-Ti-H thin films was further confirmed by Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy and by the positron Doppler broadening depth profiling method [94,95]. Positron depth-profiling was also applied to monitor the effects of hydrogenation on thin films [96]. The analysis revealed a single homogenous layer for most metal and metal hydride films, except for the Mg0.9Ti0.1Hx film, where a double layer was detected: a thin unloaded Mg0.9Ti0.1 or Mg-TiPd alloy layer on top of a hydrogenated Mg0.9Ti0.1Hx.…”

Section: Binary and Ternary Mg-based Alloysmentioning

confidence: 92%

Mg-Based Thin Films as Model Systems in the Search for Optimal Hydrogen Storage Materials

Norek¹

2012

Hydrogen Energy - Challenges and Perspectives

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“…Alloying with transition metals (TM) and changing of the composition as well as nanostructuration are a few of the methods reported to improve the properties of hydrides [141][142][143][144]. The use of palladium (Pd) as a catalyst in the MgH 2 formation has been shown to be essential [145][146][147][148][149].…”

Section: Pure Metal Hydrides (Mg Pd Ti)mentioning

confidence: 99%

A Review of the MSCA ITN ECOSTORE—Novel Complex Metal Hydrides for Efficient and Compact Storage of Renewable Energy as Hydrogen and Electricity

et al. 2020

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Hydrogen as an energy carrier is very versatile in energy storage applications. Developments in novel, sustainable technologies towards a CO2-free society are needed and the exploration of all-solid-state batteries (ASSBs) as well as solid-state hydrogen storage applications based on metal hydrides can provide solutions for such technologies. However, there are still many technical challenges for both hydrogen storage material and ASSBs related to designing low-cost materials with low-environmental impact. The current materials considered for all-solid-state batteries should have high conductivities for Na+, Mg2+ and Ca2+, while Al3+-based compounds are often marginalised due to the lack of suitable electrode and electrolyte materials. In hydrogen storage materials, the sluggish kinetic behaviour of solid-state hydride materials is one of the key constraints that limit their practical uses. Therefore, it is necessary to overcome the kinetic issues of hydride materials before discussing and considering them on the system level. This review summarizes the achievements of the Marie Skłodowska-Curie Actions (MSCA) innovative training network (ITN) ECOSTORE, the aim of which was the investigation of different aspects of (complex) metal hydride materials. Advances in battery and hydrogen storage materials for the efficient and compact storage of renewable energy production are discussed.

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Layer-resolved study of the Mg to MgH2 transformation in Mg–Ti films with short-range chemical order

Cited by 12 publications

References 16 publications

Destabilization of Mg Hydride by Self-Organized Nanoclusters in the Immiscible Mg–Ti System

Destabilization of Mg Hydride by Self-Organized Nanoclusters in the Immiscible Mg–Ti System

Mg-Based Thin Films as Model Systems in the Search for Optimal Hydrogen Storage Materials

A Review of the MSCA ITN ECOSTORE—Novel Complex Metal Hydrides for Efficient and Compact Storage of Renewable Energy as Hydrogen and Electricity

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