Perovskite-type Hydrides -Hydrogen Storage Functions and Atomistic/Electronic Structures-

Abstract

The storage of hydrogen is a crucial issue for promoting various hydrogen energy applications, and one of the promising technologies is to store hydrogen in materials as hydrides. Some ternary hydrides exhibit the perovskite structure and the formation ability has been explained on the basis of the geometric factors. In NaMgH₃, the decomposition reaction proceeds in two steps, accompanying the desorption reaction with approximately 6.0 mass% of hydrogen. Moreover, the reversible hydrogen desorption and absorption reactions of NaMgH₃ were confirmed experimentally. Two occupation sites of hydrogen anion were indicated to be related to the two-step hydrogen desorption reaction. In CaNiH₃, the starting temperature of the hydrogen desorption is lower than 400 K. CaNiH₃ as a perovskite-type hydride is continuously transformed into Ca₂NiH₄ as a complex hydride, accompanied by partial hydrogen desorption and Ni precipitation during the thermal desorption process. Intermediate state between ionic and covalent bonding among Ni and hydrogen was suggested one of the origins of continuous transformation during the thermal desorption reaction.