Synergism induced exceptional capacity and complete reversibility in Mg-Y thin films: enabling next generation metal hydride electrodes

Much of the current research into metal hydride (MH) electrodes follows the principle that the materials should be composed of hydrogen-absorbing elements (A) and non-hydrogen-absorbing elements (B). This classical design principle, however, severely limits the potential capacities of the MH electrodes (typically <400 mA h g(-1)). Herein, we demonstrate a fundamentally new strategy to design high capacity MH electrodes without using B elements by inducing synergism in the dehydrogenation process. Mg24Y5 thin films, which are composed of two strong hydrogen-absorbing elements, achieve an exceptional electrochemical hydrogen storage capacity of approximate to 1500 mA h g(-1) (5.6 wt%). All the absorbed hydrogen, including extremely stable H in YH2, can be reversibly desorbed through thermodynamic synergism. The present study provides enlightening insights to design high capacity MH electrodes and therefore enables the revival of Ni-MH batteries, and the emergence of next generation MH-air batteries.