Impact of nanostructuring on the enthalpy of formation of metal hydrides

Bérubé, Vincent; Chen, Gang; Dresselhaus, M. S.

doi:10.1016/j.ijhydene.2008.05.083

Cited by 101 publications

(54 citation statements)

References 21 publications

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“…Then an overview of the preparation techniques of metal hydride/carbon nanocomposites is given. The strong impact of carbon on the kinetics and thermodynamics of metal hydrides is highlighted for two important systems: MgH 2 and NaAlH 4 . The review will end with a summary on the opportunities and challenges in this field.…”

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confidence: 99%

The impact of carbon materials on the hydrogen storage properties of light metal hydrides

2011

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The safe and efficient storage of hydrogen is still one of the remaining challenges towards fuel cell powered cars. Metal hydrides are a promising class of materials as they allow the storage of large amounts of hydrogen in a small volume at room temperature and low pressures. However, usually the kinetics of hydrogen release and uptake and the thermodynamic properties do not satisfy the requirements for practical applications. Therefore current research focuses on catalysis and the thermodynamic tailoring of metal hydride systems. Surprisingly, carbon materials used as additive or support are very effective to improve the hydrogen storage properties of metal hydrides allowing fast kinetics and even a change in the thermodynamic properties. Even though the underlying mechanisms are not always well understood, the beneficial effect is probably related to the peculiar structure of the carbon materials. This feature article gives an introduction to the different carbon materials, an overview of the preparation strategies to synthesize carbon/hydride nanocomposites, and highlights the beneficial effect of carbon by discussing two important hydrides: MgH 2 and NaAlH 4 .

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confidence: 99%

The impact of carbon materials on the hydrogen storage properties of light metal hydrides

2011

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“…For practical applications in fact, assuming that the only relevant entropic contribution is due to the entropy loss of gaseous hydrogen, an ideal hydrogen storage system should have an enthalpy of hydride formation of about −40 kJ/ mol H 2 , in order to release hydrogen at a pressure of 10 5 Pa at room temperature. The formation of MgH 2 , however, releases 74.4 kJ/ mol H 2 , leading to an equilibrium pressure of 10 5 Pa at ϳ300°C. Tuning the thermodynamics of hydrogen absorption in Mg has so far been achieved by means of proper doping, 2,3 although this generally results in a reduction of the material's storage capacity.…”

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“…The equilibrium pressure of the Ti-buffered films is independent on the thickness of the Mg layers, indicating that surface energy effects, which would produce a thickness dependence similar to the one observed for the Pd-capped samples, are negligible. 10 The plateaus shown in Fig. 1͑a͒, corresponding to the regions of the isotherms at almost constant pressure, have widths, w, expressed in terms of optical transmission and proportional to the nominal thickness of the Mg films, d Mg .…”

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Quasifree Mg–H thin films

Baldi

Palmisano

González-Silveira

et al. 2009

Applied Physics Letters

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The thermodynamics of hydrogen absorption in Pd-capped Mg films are strongly dependent on the magnesium thickness. In the present work, we suppress such dependency by inserting a thin Ti layer between Mg and Pd. By means of optical measurements, we show that the surface energy contribution to the destabilization of MgH 2 is negligible. The inserted Ti layer prevents Mg-Pd alloy formation at the Mg/Pd interface, leading to quasifree Mg films and enhancing the kinetics of hydrogen desorption. Our observations are important for the development of thin film devices.

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“…The high density of interfaces confers to nano-systems unique physical and chemical properties, and promotes their chemical reactivity. The thermodynamics of nano-scaled systems is strongly altered with respect to bulk material and size-dependent effects [1,2], becoming more and more complicated when dealing with compounds and heterogeneous ones [3]. Far from putting a limit to the exploitation of nanoparticles, this fascinating behavior allows for the tailoring of material properties by designing unique functional devices at nanoscale.…”

Section: Introductionmentioning

confidence: 99%

“…In presence of hysteresis, the equilibrium pressure p eq H 2 is calculated as the geometric average of the absorption (p abs ) and desorption (p des ) plateau pressures. The hysteresis is usually quantified by the ratio: ∆G hyst its = RT ln p abs p des bulk (2) Additional sources of strain, such as the presence of defects or interfaces in the material, can lead to a wider extrinsic hysteresis, as shown in Figure 1b, where the equilibrium pressure is not altered because of the symmetrical shift of both absorption and desorption plateau. A simple relation between ∆G …”

Section: Introductionmentioning

confidence: 99%

Interface Enthalpy-Entropy Competition in Nanoscale Metal Hydrides

2018

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Abstract:We analyzed the effect of the interfacial free energy on the thermodynamics of hydrogen sorption in nano-scaled materials. When the enthalpy and entropy terms are the same for all interfaces, as in an isotropic bi-phasic system, one obtains a compensation temperature, which does not depend on the system size nor on the relative phase abundance. The situation is different and more complex in a system with three or more phases, where the interfaces have different enthalpy and entropy. We also consider the possible effect of elastic strains on the stability of the hydride phase and on hysteresis. We compare a simple model with experimental data obtained on two different systems:(1) bi-phasic nanocomposites where ultrafine TiH 2 crystallite are dispersed within a Mg nanoparticle and (2) Mg nanodots encapsulated by different phases.

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Impact of nanostructuring on the enthalpy of formation of metal hydrides

Cited by 101 publications

References 21 publications

The impact of carbon materials on the hydrogen storage properties of light metal hydrides

The impact of carbon materials on the hydrogen storage properties of light metal hydrides

Quasifree Mg–H thin films

Interface Enthalpy-Entropy Competition in Nanoscale Metal Hydrides

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