Cycle stability of La-Mg-Ni based hydrogen storage alloys in a gas–solid reaction

The cycle stability of La-Mg-Ni based alloys in a gas–solid reaction system was investigated in this work. Both partial substitutions of La and Ni by Ce and Al, respectively, improved the cycle stability of La_(0.65−x)Ce_xCa_1.03Mg_1.32Ni_(9−y)Al_y alloys. Although the addition of Al reduced the hydrogen storage capacity significantly, it is still important to be included in the system for its superior property in improving the cycle life. Hence, two optimized samples with a small addition of Al (y = 0.10) were used to compare with the cycle life of CaNi₅. It was found that the Ce and Al added samples have a better hydrogen capacity retention than that of samples without element substitution; and their overall hydrogen storage capacity was still higher than that of CaNi₅. We also found that heat treatment used in this study did not fully recover the hydrogen storage capability of La-Mg-Ni based alloy to its original storage capacity. A probable reason was the heat treatment used in this study could only recover the degradation caused by the disproportionation to some extent, but the treatment was unable to reverse the degradation caused by decrepitation.