Mechanochemical synthesis of Ce₃Al₁₁ powder and its catalytic effect on the hydrogen sorption properties of NaAlH₄

Mechanochemical synthesis of the Ce₃Al₁₁ powder was performed through a reaction among CeCl₃, AlCl₃ and NaH powders. α-Ce₃Al₁₁ particles with an average size of 250 nm were obtained. The catalytic effect of the synthesized Ce₃Al₁₁ on the hydrogen sorption properties of NaAlH₄ was investigated. The hydrogen absorption kinetics of NaAlH₄ with Ce₃Al₁₁ was significantly enhanced and the hydrogen capacity was improved compared to those properties of NaAlH₄ with CeCl₃. This can be attributed to the fine distribution of the Ce₃Al₁₁ catalyst in NaAlH₄ during ball milling. Although the volume of the NaAlH₄ pellets generally tends to increase during the hydrogen sorption cycles, the volume expansion of the pellet of NaAlH₄ with Ce₃Al₁₁ was relatively low with a small pore fraction compared to that of the pellet of NaAlH₄ with conventional chloride catalysts such as CeCl₃, TiCl₃ and TiCl₄. The use of a nonchloride catalyst appears to provide an effective approach for suppressing the volume expansion of NaAlH₄ pellets during the hydrogen sorption cycles.