Electrochemical properties of hypo-stoichiometric Y-doped AB2 metal hydride alloys at ultra-low temperature

Abstract

The structure, gaseous phase, and electrochemical hydrogen storage properties of two series of Y-doped AB2 metal hydride alloys were compared. While the stoichiometry (B/A ratio) of the average alloy composition of the first series is maintained at 1.99 (Ti12Zr21.5V10Cr7.5Mn8.1Co8.0−xNi32.2YxSn0.3Al0.4), those in the second series decrease from 1.99 to 1.83 ((TiZr)(VCrMnNiSnAl)1.75Co0.24−3xYx). Since the solubility of Y in the main phase (C14) is limited (0.1–0.2at.%), the influences of Y are through the changes in the composition and abundance of the main and secondary phases. While TiNi phase is considered beneficial to activation, surface reaction area, and surface charge-transfer, YNi phase is on the contrary. By adjusting the stoichiometry, we were able to increase the TiNi-to-YNi ratio and lower the −40°C charge-transfer resistance by increasing the surface reaction area while maintaining the same surface catalytic ability. The lowest −40°C charge-transfer resistance was obtained through an AB2 alloy with 0.4at.% Y and a B/A ratio of 1.93. Further improvement in the ultra-low temperature performance of the AB1.93 alloy is expected by combining the current result with other modifiers, such as Si, to improve the surface catalytic ability.