Construction of Mg/Zr superlattice structure to achieve efficient hydrogen storage via atomic-scale interaction in Mg-Zr modulation films

Mg-based alloys have great potential for application owing to their high hydrogen storage capacity but still suffer from too high temperature to absorb/desorb hydrogen due to overly stable de/hydriding thermodynamics and poor kinetics. To overcome this barrier, in this work, atomic-scale superlattice structures have been successfully fabricated in Mg-Zr modulation films using a self-designed semi-co-sputtering method. For comparison, Mg/Zr multilayer films with thicker layers are also prepared. The Mg/Zr interface density in Mg-Zr modulation films is much higher than in Mg/Zr multilayer films, thus exhibiting different structure changes in hydrogenation and excellent hydrogen storage properties. Transmission electron microscopy observation shows that the as-deposited Mg-Zr modulation films have ultra-thin coherent layers and grow along the [0001] direction. These modulated films keep their original lattice structure after de/hydrogenation, indicating the formation of solid solution with the entering of hydrogen atoms into the film. In contrast, the Mg/Zr multilayer films form MgH2 phase after hydrogenation. The Mg-Zr modulation film absorbs hydrogen at room temperature and begins to release hydrogen at approximately 81 degrees C, whereas the hydrogen release temperature of the conventional MgH2 and the present Mg/Zr multilayer film is about 287 and 171 degrees C, respectively. DFT calculation further reveals that the great enhancement of the above-mentioned properties can be attributed to the synergetic effect of Zr catalysis and strain induced by coherent heterointerfaces. The present work provides a new insight for developing Mg-based hydrogen storage alloys.