Enhanced Reactivation of Non-Pyrophoric Lanthanum-Modified AB2 Alloys for Hydrogen Storage

Abstract

AB2 as hydrogen storage materials could provide an alternative path to compressed and liquid hydrogen for stationary applications. However, applications of these alloys are limited by the highly pyrophoric nature of AB2 powders once hydrogen-activated. Self-ignition and combustion of the alloy powder upon air exposure leaves no possibility for reusing the alloy. In this study, a non-pyrophoric AB2 alloy, Ti0.856Zr0.122La0.05Mn0.92Cr0.59Co0.15Fe0.05(VFe)0.29, that can be exposed to air and then reactivated at ambient temperature was successfully developed. Lanthanum substitution in the alloy induced the formation of La-rich secondary phases that were found to protect the alloy against extensive oxidation, while cobalt sites would remain protected to facilitate the initial catalytic splitting of hydrogen molecules in the gas phase before their diffusion within the bulk of the alloy. Upon hydrogen exposure, the La secondary phases were also found to form LaH3, and these were believed to further act as “hydrogen pumps” delivering hydrogen to the alloy grain boundaries. This balance in the number of phases that can reversibly oxidize and be protected against oxidation, coupled with the larger grains observed upon La addition are believed to confer the non-pyrophoric alloy reported in this work with unique properties. This includes superior hydrogen (re)activation with fast hydrogen kinetics, and a 91% retention of the initial hydrogen capacity even upon full exposure to air.