MgH₂ has become a hot spot in the research of hydrogen storage materials, due to its high theoretical hydrogen storage capacity. However, the poor kinetics and thermodynamic properties of hydrogen absorption and desorption seriously hinder the development of this material. Ti-based materials can lead to good effects in terms of reducing the temperature of MgH₂ in hydrogen absorption and desorption. MXene is a novel two-dimensional transition metal carbide or carbonitride similar in structure to graphene. Ti₃C₂ is one of the earliest and most widely used MXenes. Single-layer Ti₃C₂ can only exist in solution; in comparison, multilayer Ti₃C₂ (ML-Ti₃C₂) also exists as a solid powder. Thus, ML-Ti₃C₂ can be easily composited with MgH₂. The MgH₂+ML-Ti₃C₂ composite hydrogen storage system was successfully synthesized by ball milling. The experimental results show that the initial desorption temperature of MgH₂-6 wt.% ML-Ti₃C₂ is reduced to 142 °C with a capacity of 6.56 wt.%. The E_a of hydrogen desorption in the MgH₂-6 wt.% ML-Ti₃C₂ hydrogen storage system is approximately 99 kJ/mol, which is 35.3% lower than that of pristine MgH₂. The enhancement of kinetics in hydrogen absorption and desorption by ML-Ti₃C₂ can be attributed to two synergistic effects: one is that Ti facilitates the easier dissociation or recombination of hydrogen molecules, while the other is that electron transfer generated by multivalent Ti promotes the easier conversion of hydrogen. These findings help to guide the hydrogen storage properties of metal hydrides doped with MXene.

The unique properties of two-dimensional (2D) materials make them increasingly attractive in various fields, especially for energy harvesting, conversion, or storage. Simultaneously, numerous synthetic methods have been rapidly developed. Recently, topochemical strategies were demonstrated, and they show tremendous promising potential for synthesizing 2D materials due to their simplicity, scalability, and high efficiency. Considering the suitability of material structures and their synthesis methods, as well as the relationship between material properties and applications, it is necessary for researchers to comprehensively review and determine the prospects of 2D materials based on topological chemical synthesis methods and their related applications. Therefore, in this review, we systematically summarize and analyze the representative topochemical strategies for synthesizing 2D materials, including salt-templating methods for non-layered 2D materials, molten Lewis acid etching strategy for novel MXenes, and the chalcogen vapors etching and substituting strategy for phase-controlled 2D materials and so on, with the application of these 2D materials in energy-related fields including batteries, supercapacitors, and electrocatalysis. At the end of the paper, the corresponding perspective was also illustrated, and we expect that this could provide a reference for the future research in the field.