Melt‐Spinning of AB_5.5‐Type Hydride‐Forming Compounds and the Influence of Annealing on Electrochemical and Crystallographic Properties

Abstract

Abstract Non‐stoichiometric almost single‐phase AB 5.5 materials were prepared using the melt‐spinning technique. Characteristic of these materials is the anisotropically deformed crystal lattices (decreased a ‐axis and increased c ‐xis), resulting from the excess of B‐elements incorporated in the hP6‐CaCu 5 structure. These materials show (i) an excellent long‐term stability during electrochemical cycling in alkaline solution, indicating that the oxidation resistivity strongly depends on the extent of the crystal lattice deformation and (ii) a relatively poor electrocatalytic activity which can be attributed to the absence of highly catalytic second‐phase alloys. Annealing of the as‐prepared samples induces the deformed crystal lattice to relax by secreting the excess of B‐elements. As a consequence, double‐phase materials are formed, consisting of hydride‐forming compounds with compositions close to the AB 5 stoichiometry and second‐phase alloys. These double‐phase materials combine a relatively poor long‐term cycling stability with a high electrocatalytic activity.