Abstract
The hydrogenation and dehydrogenation behavior of LaNi5−xAlx (x=0–0.5) was studied by the pressure differential scanning calorimetry (PDSC) at the hydrogen pressure range of 1 to 5 MPa in the temperature range from 323 to 573 K with the heating and cooling rates of 2 to 30 K min−1. In the heating runs of the hydride with x≤0.1 two endothermic peaks were observed. With the increase in the aluminum content, the first peak at lower temperature decreased, while the second peak at higher temperature increased. Furthermore, the difference in the temperatures of the peak top decreased with the increase in the aluminum content. In the heating runs of the hydride with x>0.1 only one endothermic peak was observed. These endothermic peaks shifted to higher temperatures with the increase in the hydrogen pressure. Using Ozawa’s method, the activation energies for dehydrogenation and hydrogenation processes were estimated. The activation energy for the dehydrogenation process of the hydrides increased with the increase in the hydrogen pressure and the aluminum content. However, the dependence of the activation energy on the aluminum concentration in the range of x≥0.1 was different from that of x<0.1. The activation energy for the hydrogenation process was estimated only in the range of x>0.1 at the hydrogen pressure of 5 MPa. The value of activation energy for the hydrogenation was lower than that for the dehydrogenation.
