Hydrogen diffusion kinetics and structural integrity of superhigh pressure Mg-5 wt%Ni alloys with dendrite interface

• A Mg-Ni alloy with fine dendrite arm was firstly achieved by high pressure method.
• Unique dendrite arm structure enhances hydrogen desorption kinetics and integrity.
• A “zig-zag” jump of H atom along {11−20} prismatic planes results in fast kinetics.
• Cycle structure integrity is effectively improved by large defect space.

A strategy of low-angle orientation dendrite interface-high index planes-which prepared by super-high pressure (SHP) technique, is proposed and successfully improved the hydrogen storage properties of Mg based materials for the first time, wherein a simple binary Mg-Ni alloy is used as a sample to elucidate its related mechanisms. The phase composition, morphology variation and hydrogen storage properties of the as-cast and SHP Mg-5Ni alloys in the temperature range of 1100–1600 °C are systemically investigated. The reversible hydrogen storage capacities and plateau hydrogen pressure of the as-cast and SHP alloys are close due to the same hydrogen storage phases (Mg and Mg2Ni). Note that although SHP treatment at 1600 °C has a large weight fraction of Mg6Ni compound, it still effectively reduces the onset temperature of dehydriding (∼262 °C), as well as improves the hydrogen desorption kinetics at low temperatures and structural integrity. The low onset temperature and outstanding hydrogen sorption/desorption kinetics are mainly associated with the formation of a large number of dendrite interface, in which the hydrogen atoms readily occur “zig-zag” jumps along {11−20} prismatic planes. This dendrite interface of high index planes which prepared by SHP technique paves a new pathway to enhance the hydrogen storage performances of magnesium based alloys.