NSTI Nanotech 2009

Computational Modeling of Pressure-Composition-Temperature Curves for Hydrogen Storage Materials

V. Tserolas, M. Katagiri
National Institute for Materials Science, JP

Keywords: hydrogen storage materials, P-C-T curve, computational model

Abstract:

For the calculation of P-C-T curves by computer simulations, without relying on optimization of parameters based on experimental data, we consider the use of quantum mechanical methods for computing the structural, electronic, energetic, and kinetic properties of metal hydride materials. The specific method we use is the periodic plane wave density functional theory (DFT). The DFT method can then be used to optimize the atomic coordinates of each atom in the unit cell, the volume, and the shape of the unit cell. More importantly, the DFT method can be used to estimate the site energies and the lattice expansion parameter for metal hydrides. Moreover, in the absence of hydrogen-hydrogen interaction, as we assumed in the model, the average number of hydrogen atoms is simply given by the Fermi-Dirac distribution function. In the presence of hydrogen-hydrogen interaction, the chemical potential has to be calculated by considering and other contributions. For example, the effective elastic interaction, the direct electronic interaction, the partial configurational entropy of the hydrogen atoms, and the vibration of hydrogen atoms in the host lattice have to be encountered. RNi5 metal hydride materials have been simulated at different temperatures. These materials have been thoroughly characterized with respect to their physical and electrochemical performance. The simulations demonstrate good agreement with the experimental data reported for various RNi5-type hydrogen storage materials. The plateau pressure increases with increasing temperatures. It also becomes more difficult to insert hydrogen atoms at higher temperatures.
 
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