MXenes for magnesium-based hydrides: A review

Over the last few decades, hydrogen fuel has been considered to be a major alternative source of renewable energy due to increasing environmental pollution and the depletion of nonrenewable energy. The need to efficiently produce and store hydrogen, therefore, has necessitated the development of several technologies and materials for hydrogen storage to achieve the envisaged hydrogen economy. Solid-state hydrogen storage in magnesium hydride (MgH2) has shown a huge potential owing to its impressively high gravimetric and volumetric hydrogen capacities of ca. 7.6 wt% and 111 g/L, respectively. However, the bottleneck to the wide applications of MgH2 as a commercial source of hydrogen fuel is the delivery temperature requirement of ca. 300400 degrees C due to thermodynamic stability (ca. 76 kJ/mol-H2), and the slow kinetics of hydrogen de/absorption. Nanostructuring and catalysis are marked as the most promising strategies for modifying the properties of MgH2. Doping MgH2 with nanoscale materials can lower the delivery temperature and bring it nearer to commercial applications. Recently, MXenes, a group of 2D nanomaterials composed of transition metal carbides/nitrides/ carbonitrides layers, have demonstrated the dual roles of storing hydrogen and enhancing the hydrogen evolution reactions of lightweight metal hydrides especially MgH2. This review article, therefore, provides explicit insights into MXenes, their recent applications as potential materials for storing hydrogen, and as functional additives for enhancing the hydrogen reaction of MgH2 with an outlook.