Achievement in modifying dehydrogenation kinetics for Sc-containing Mg matrix in Mg–Y–Zn alloy

Abstract

To eliminate the adverse effects of coarse α-Mg phase on the hydrogen storage kinetics of Mg-rich alloys, element Sc with high solid solubility in α-Mg is introduced into Mg–Y–Zn alloy initiatively, which shows positive effects to enhance the hydrogen storage performance. The Sc-doping effectively enhances the dehydrogenation kinetics by motivating the formation of abundant stacking faults. The stacking faults provide the hydrogen atoms with diffusion channels to accelerate the mutual phase transformation of metal/hydride. With 1 at.% Sc substituting for Y, the apparent activation energy for dehydrogenation obtains a 11% reduction compared with Sc-free alloy. Besides, Sc-doping facilities the decomposition of YH3, which provides “electron transfer” effect to accelerate the decomposition of MgH2. Sc-doping affects the hydrogenation behavior by weakening the H2 sorption but ensuring the H atoms diffusion in Mg matrix. With the gradually substitution of Sc for Y, the developed dendrite arms make it difficult for hydrogen to diffuse deeper into the samples, resulting in large ratio of unhydrided Mg. It can be concluded that the quantity of defects within Mg and catalytic sites outside the Mg matrix are important for achieving rapid hydrogen absorption and desorption simultaneously.