A new methodology for extra enhancement of hydrogen storage capacity of Mg–Ni based alloys: The role of gaseous O2/H2 mixture

Abstract

In the present study, Mg–5Ni and Mg–15Ni alloys are prepared, and their (de)hydrogenation properties are investigated by thermal desorption spectroscopy (TDS). A new hydrogenation condition is developed to improve the hydrogen uptake properties of the Mg–Ni alloy. It is found that the hydrogen absorption and thermal desorption properties of both alloys are extremely sensitive to the presence of 3% O2 in the hydrogenation environment. Although O₂ accelerates hydrogen absorption, it lowers the desorption temperature and reduces the hydrogen storage capacity of the Mg–Ni alloy by consuming Mg₂Ni if it is added in every cycle. The hydrogen storage capacity of Mg–Ni alloys can be significantly increased by adding oxygen only in the second cycle instead of in all cycles. In the early stages of hydrogenation, only two TDS peaks are observed, while in later cycles a new peak appears at higher temperatures. These peaks correspond to the decomposition of Mg₂NiH₄ (peak 1), MgH₂ (peak 2), and the release of hydrogen from the bulk material (peak 3). It is also evident that the Mg–15Ni sample has a better hydrogen storage capacity than the Mg–5Ni sample.