Two-dimensional material MXene and its derivatives enhance the hydrogen storage properties of MgH2: A review and summary

Mg-based hydrogen storage alloys are a very promising hydrogen storage material in terms of mass and bulk hydrogen storage density, safety, stability and convenience, and very much in line with the specifications for in-vehicle use. However, MgH2 has been limited by high thermodynamic stability, slow hydrogen absorption/release kinetics, and short cycle life and has not been applied in the field of energy storage. For this reason, researchers have done extensive work to improve the kinetic and thermodynamic properties of MgH2 and have made relatively good progress. As an emerging member of the two-dimensional nanomaterial family, MXene has shown promising applications in clean energy production, conversion, and storage due to its two-dimensional layered structure, unique interlayer spacing, high specific surface area, and excellent chemical/physical stability. In particular, it showed excellent catalytic ability in modifying the hydrogen absorption/release properties of MgH2. Furthermore, MXene has the advantages of tunable components, abundant surface termini, and controllable layer thickness, which makes MXene both a highly active catalyst for MgH2 and an ideal nanoconfined carrier. In this article, we present the reader with an overview and elucidation of the development of the main methods for the preparation of MXene nanosheets and their derivatives in recent years and discuss the advantages or disadvantages of different synthesis strategies for obtaining MXene with different uses and properties. Meanwhile, the research progress of MXene as catalysts or carriers in enhancing the kinetic performance of hydrogen uptake/release of MgH2 was summarized, and the effects of different types of MXene on the kinetics and thermodynamics of MgH2 hydrogen uptake/release and their catalytic mechanisms were highlighted. The positive effects of MXene and its derivatives on the hydrogen uptake/release behavior of Mg/MgH2 were comprehensively and objectively evaluated. It also provides insights into the opportunities and challenges of designing and synthesizing highly active MXene catalysts for hydrogen storage.