Effects of REF3 (RE = Y, La, Ce) additives on dehydrogenation properties of LiAlH4

The catalytic effects of rare earth fluoride REF3 (RE = Y, La, Ce) additives on the dehydrogenation properties of LiAlH4 were carefully investigated in the present work. The results showed that the dehydrogenation behaviors of LiAlH4 were significantly altered by the addition of 5 mol% REF3 through ball milling. The destabilization ability of these catalysts on LiAlH4 has the order: CeF3>LaF3>YF3. For instance, the temperature programmed desorption (TPD) analyses showed that the onset dehydrogenation temperature of CeF3 doped LiAlH4 was sharply reduced by 90 °C compared to that of pristine LiAlH4. Based on differential scanning calorimetry (DSC) analyses, the dehydriding activation energies of the CeF3 doped LiAlH4 sample were 40.9 kJ/mol H2 and 77.2 kJ/mol H2 for the first and second dehydrogenation stages, respectively, which decreased about 40.0 kJ/mol H2 and 60.3 kJ/mol H2 compared with those of pure LiAlH4. In addition, the sample doped with CeF3 showed the fastest dehydrogenation rate among the REF3 doped LiAlH4 samples at both 125 °C and 150 °C during the isothermal desorption. The phase changes in REF3 doped LiAlH4 samples during ball milling and dehydrogenation were examined using X-ray diffraction and the mechanisms related to the catalytic effects of REF3 were proposed.