Effects of carbon monoxide on the hydriding reactions of the untreated and fluorinated LaNi4.7Al0.3 alloys

Abstract

A method for the surface treatment of the hydriding alloys has been developed to improve the hydriding properties. After F-treatment, LaF3 was formed on the outer surface and metallic Ni was precipitated in a subsurface for the LaNi4.7Al0.3 alloy. By utilizing the unique surface characteristics, the effects of carbon monoxide on hydriding reaction rates and hydrogen absorbing capacities were investigated by cyclic hydriding/dehydriding (H/D) tests. The degradation of hydriding reaction rate and hydrogen capacity of the fluorinated alloy was found considerably small even under the existence of the extremely poisonous impurity CO (H2 + 1000 ppm CO) at lower temperatures. In contrast, the gas mixture deactivates the untreated alloy severely under the same conditions. It was also found that even if the fluorinated alloy was deactivated after repeating many H/D cycles in the gas mixture, the reactivity can be easily recovered by only a cycle of H/D reaction in pure hydrogen. This offers the possibility to move toward practical metal hydride-based applications, especially under the existence of impurities.