Mechanism of increased performance and durability of Pd-treated metal hydriding alloys

Mechanical grinding a small amount of palladium or platinum with AB5 type intermetallic hydrogen storage alloys was shown to greatly improve the hydrogen absorption and desorption performances of the alloys. The alloys with the treatment could be activated under sub-atmospheric hydrogen pressure at room temperature and absorb and desorb hydrogen at faster rates, and they retained both the low activation pressures and fast absorption and desorption rates even after more than two years of exposure in open air. The surface structure and composition of the hydrogen storage alloys before and after aging were characterized by SEM and XPS analyses. The processes that account for the degradation of performance with aging and the enhanced performance of the palladium or platinum treated alloys were discussed. It was found that enhanced hydrogen spillover and reverse hydrogen spillover were the primary processes that account for the improved hydrogen storage performance after palladium or platinum treatment.