Enhanced hydrogen storage performance of magnesium hydride with incompletely etched Ti₃C₂T_x: The nonnegligible role of Al

The pronounced enhancement on the hydrogen storage performance of MgH₂ has been achieved by completely etched MXenes. However, whether the completely removal of Al is necessary and what role the residual Al can play are still unresolved issues. Herein, for the first time, Ti₃C₂T_x MXenes with different residual Al are prepared to improve the hydrogen storage performance of MgH₂. The result shows that the proper residual Al for incompletely etched Ti₃C₂T_x has a very important responsibility for the improvement of catalytic activity. Different with metallic Al and other Al-containing additives, the unique Ti-Al metallic bonds assisted by surface functional group (-O) can change the electronic structure of Al, which not only hinder the formation of Mg-Al alloys, but also assist the escape of H atoms from MgH₂ and enhance the absorption of H atom on catalyst. Meanwhile, the de/hydrogenation process of MgH₂ can further be enhanced by multivalent Ti. This report will arouse attention for incompletely etched MXenes and provide a new strategy to optimize properties of MXenes in various fields.