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

The structure, gaseous phase, and electrochemical hydrogen storage properties of two series of Y-doped AB(2) 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)(1.75)Co0.24 3xYx). Since the solubility of Y in the main phase (C14) is limited (0.1-0.2 at.%), 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 degrees C charge-transfer resistance by increasing the surface reaction area while maintaining the same surface catalytic ability. The lowest -40 degrees C charge-transfer resistance was obtained through an AB(2) alloy with 0.4 at.% Y and a B/A ratio of 1.93. Further improvement in the ultra-low temperature performance of the AB(1.93) alloy is expected by combining the current result with other modifiers, such as Si, to improve the surface catalytic ability. (C) 2015 Elsevier B.V. All rights reserved.