Surface properties and activation

Schlapbach, Louis

doi:10.1007/3-540-54668-5_9

Cited by 49 publications

(41 citation statements)

References 363 publications

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“…20). The operating temperature of a metal hydride system is fixed by the plateau pressure in thermodynamic equilibrium and by the overall reaction kinetics 21 .…”

Section: Hydrogen Storage By Metal Hydridesmentioning

confidence: 99%

Hydrogen-storage materials for mobile applications

Schlapbach

Züttel

2001

Nature

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7,774

4,566

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Energy can be stored in different forms: as mechanical energy (for example, potential energy or rotation energy of a flywheel); in an electric or magnetic field (capacitors and coils, respectively); as chemical energy of reactants and fuels (batteries, petrol or hydrogen); or as nuclear fuel (uranium or deuterium). Chemical and electric energy can be transmitted easily because they both involve electronic Coulomb interaction. Chemical energy is based on the energy of unpaired outer electrons (valence electrons) eager to be stabilized by electrons from other atoms. The hydrogen atom is most attractive because its electron (for charge neutrality) is accompanied by only one proton. Hydrogen thus has the best ratio of valence electrons to protons (and neutrons) of all the periodic table, and the energy gain per electron is very high.Hydrogen is the most abundant element on Earth, but less than 1% is present as molecular hydrogen gas H 2 . The overwhelming majority is chemically bound as H 2 O in water and some is bound to liquid or gaseous hydrocarbons. The clean way to produce hydrogen from water is to use sunlight in combination with photovoltaic cells and water electrolysis (see review in this issue by Grätzel, pages 338-344). Other forms of primary energy and other water-splitting processes are also used: the hydrogen consumed today as a chemical raw material (about 5 ǂ10 10 kg per year worldwide) is to a large extent produced using fossil fuels and the reaction of hydrocarbon chains (-CH 2 -) with H 2 O at high temperatures, which produces H 2 and CO 2 . Direct thermal dissociation of H 2 O requires temperatures higher than 2,000 ᑻC (>900 ᑻC with a Pt/Ru catalyst).The chemical energy per mass of hydrogen ) is at least three times larger than that of other chemical fuels (for example, the equivalent value for liquid hydrocarbons is 47 MJ kg -1 ). Once produced, hydrogen is a clean synthetic fuel: when burnt with oxygen, the only exhaust gas is water vapour, but when burnt with air, lean mixtures have to be used to avoid the formation of nitrogen oxides. Whether hydrogen can be considered a clean form of energy on a global scale depends on the primary energy that is used to split water 1 . The availability of free energy is often unsafe. The mechanical energy of a 1,000-kg car running out of control at 40 km h -1 can kill pedestrians. The process of burning hydrogen can be done in an efficient and controlled way to liberate energy at a desirable rate, or in an uncontrolled way with the potential to cause damage. For historical reasons hydrogen has a bad reputation, which is not altogether justified: a more recent analysis 2 of the Hindenburg catastrophe shows that the air ship caught fire because of a highly flammable skin material and not because of the hydrogen gas it contained. The safety of hydrogen relies on its high volatility and non-toxicity.Today, many scientists and engineers, some companies, governmental and non-governmental agencies and even finance institutions are convinced that hydrogen's physical...

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“…20). The operating temperature of a metal hydride system is fixed by the plateau pressure in thermodynamic equilibrium and by the overall reaction kinetics 21 .…”

Section: Hydrogen Storage By Metal Hydridesmentioning

confidence: 99%

Hydrogen-storage materials for mobile applications

Schlapbach

Züttel

2001

Nature

Self Cite

7,774

4,566

View full text Add to dashboard Cite

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“…After dissociation at the metal surface ͑M s ͒ the hydrogen atoms are chemically adsorbed ͑H ad ͒ and then converted to the absorbed state ͑H abs ͒ in the first atomic layer, which has been denoted as the sublayer or subsurface. 8 Subsequently, hydrogen is transported into the bulk of the material ͑M b ͒ by conventional diffusion. In Fig.…”

Section: A System Descriptionmentioning

confidence: 99%

“…1, respectively. [7][8][9][10][11] During hydrogen absorption at low concentrations, a solid solution is formed, which is generally denoted as the ␣ phase. In this concentration region the partial hydrogen pressure ͑P H 2 eq ͒ is clearly dependent on the amount of stored hydrogen.…”

Section: Introductionmentioning

confidence: 99%

Modeling of hydrogen storage in hydride-forming materials: Equilibrium gas-phase kinetics

Ledovskikh

Danilov²,

Notten

2007

Phys. Rev. B

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A kinetic model has been developed, describing the kinetics of the hydrogen storage reactions in hydrideforming materials under equilibrium conditions. Based on first principles chemical reaction kinetics and statistical thermodynamics, the model is able to describe the complex processes occurring in hydrogen storage systems, including phase transitions. A complete set of equations, governing pressure-composition isotherms in both solid-solution and two-phase coexistence regions has been obtained. General expressions for rate constant dependencies have been proposed, using well-defined phase-dependent Hamiltonians for the hydrogen energy state at the surface and in the bulk of hydride-forming materials. The characteristics of both model ͑LaNi y Cu 1.0 ͒ and commercial, misch-metal-based AB 5 -type materials at different compositions and temperatures have been simulated. Good agreement between experimental and theoretical results for the pressurecomposition isotherms has been found in all cases.

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“…1͑a͒ and 1͑b͒, respectively. [8][9][10][11][12] During hydrogen absorption at low concentrations, a solid solution is formed, which is generally denoted as the ␣ phase. In this concentration region, the partial hydrogen pressure ͑P H 2 eq ͒ is clearly dependent on the amount of stored hydrogen.…”

Section: Introductionmentioning

confidence: 99%

Modeling of hydrogen storage in hydride-forming materials: Statistical thermodynamics

Ledovskikh

Danilov²,

Rey³

et al. 2006

Phys. Rev. B

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A new lattice gas model has been developed, describing the hydrogen storage in hydride-forming materials. This model is based on the mean-field theory and Bragg-Williams approximation. To describe first-order phase transitions and two-phase coexistence regions, a binary alloy approach has been adopted. A complete set of equations describing pressure-composition isotherms and equilibrium electrode potential curves of hydride forming materials in both solid-solution and two-phase coexistence regions has been set up. The proposed model defines both the equilibrium pressure and equilibrium potential as explicit functions of the normalized hydrogen concentration, using eight physically well-defined parameters. Gibbs free energies, entropies, and phase diagrams of both model ͑LaNi y Cu 1.0 ͒ and commercial, MischMetal-based, AB 5 -type materials at different compositions and temperatures have been simulated. Good agreement between experimental and theoretical results for the pressure-composition isotherms obtained in the gas phase and the equilibrium potential curves measured in electrochemical environment has been found in all cases.

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Surface properties and activation

Cited by 49 publications

References 363 publications

Hydrogen-storage materials for mobile applications

Hydrogen-storage materials for mobile applications

Modeling of hydrogen storage in hydride-forming materials: Equilibrium gas-phase kinetics

Modeling of hydrogen storage in hydride-forming materials: Statistical thermodynamics

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