Influence of Al- and Cu-doping on the thermodynamic properties of the LaNiIn-H system

The Pressure-Composition-Temperature (P-C-T) relations for the LaNiIn, LaNi0.95Cu0.05In and LaNiIn0.98Al0.02-H systems were measured by a volumetric Sieverts' method at 398-423 K. All isotherms show plateau pressure regions indicating equilibria between two hydride phases. The replacements of Ni by Cu and In by Al affect the P-C-T diagrams, stability of the hydrides, homogeneity regions of the hydrides formed, slope of the isotherms and critical temperatures of the β-γ transition. In addition, the Cu-doping induces a significant hysteresis between the hydrogen absorption and desorption processes. The relative partial molar thermodynamic properties for the studied systems are: ΔHH = −34.6 ± 2.1 kJ (molH)−1, ΔSH = −70.7 ± 3.6 J (K·molH)−1 for LaNiIn-H; ΔHH = −34.1 ± 0.5 kJ (molH)−1, ΔSH = −74.9 ± 1.0 J (K·molH)−1 for LaNi0.95Cu0.05In-H; ΔHH = −33.2 ± 0.8 kJ (molH)−1, ΔSH = −68.3 ± 1.2 J(K·molH)−1 for LaNiIn0.98Al0.02-H.