Investigation of the Hydrogen Absorption by the LaNi 5 and LaNi 4.75 Pb 0.25 Alloys Using a Statistical Physics Model.

A theoretical model was selected among three potentially applicable models and then used to analyze the absorption isotherms of the hydrogen storage alloys LaNi5 and LaNi4.75Pb0.25 at three different temperatures (T = 303 K, 313 K, 323 K). The theoretical expressions of the model were based on the statistical physics formalism and simplifying hypotheses. The model selected was the one with the highest correlation with the experimental data. The model had six adjustable parameters: the number of hydrogen atoms per site n α , n β , the receptor site densities N α , N β and the energy parameters P α , P β . The fitted parameters obtained for the Pb-doped and nondoped alloys were compared and discussed in relationship to the absorption isotherms. Finally, the fitted parameters or the model were further applied to calculate thermodynamic functions, such as entropy, Gibbs free energy and internal energy, which govern the absorption mechanism. [ABSTRACT FROM AUTHOR]