Nanostructured MXene-based materials for boosting hydrogen sorption properties of Mg/MgH2

Hydrogen holds the advantages of high energy density, great natural abundance and zero emission, making it suitable for large scale and long term energy storage, while its safe and efficient storage is still challenging. Among various solid state hydrogen storage materials, MgH2 is promising for industrial applications due to its high gravimetric and volumetric hydrogen densities and the abundance of Mg on earth. However, the practical application of MgH2 has been limited by its stable thermodynamics and slow hydrogen desorption kinetics. Nanocatalysis is considered as a promising approach for improving the hydrogen storage performance of MgH2 and bringing it closer to the requirements of commercial applications. It is worth mentioning that the recently emerging two-dimensional material, MXene, has showcased exceptional catalytic abilities in modifying the hydrogen storage properties of MgH2. Besides, MXene possesses a high surface area, excellent chemical/physical stability, and negatively charged terminating groups, making it an ideal support for the "nanoconfinement" of MgH2 or highly active catalysts. Herein, we endeavor to provide a comprehensive overview of recent investigations on MXene-based catalysts and MXene supports for improving the hydrogen sorption properties of Mg/MgH2. The mechanisms of hydrogen sorption involved in Mg-MXene based composites are highlighted with special emphases on thermodynamics, kinetics, and catalytic behaviors. The aim of this work is to provide a comprehensive and objective review of researches on the development of high-performance catalysts/supports to improve hydrogen storage performances of Mg/MgH2 and to identify the opportunities and challenges for future applications.