Nanostructuring of Mg-Based Hydrogen Storage Materials: Recent Advances for Promoting Key Applications

With the depletion of fossil fuels and global warming,there is an urgent demand to seek green,low-cost,and high-efficiency energy resources.Hydrogen has been considered as a potential candidate to replace fossil fuels,due to its high gravimetric energy density(142 MJ kg-1),high abundance（H2O）,and environmentalfriendliness.However,due to its low volume density,effective and safe hydrogen storage techniques are now becoming the bottleneck for the"hydrogen economy".Under such a circumstance,Mg-based hydrogen storage materials garnered tremendous interests due to their high hydrogen storage capacity（～7.6 wt% for MgH2）,low cost,and excellent reversibility.However,the high thermodynamic stability(ΔH=-74.7 kJ mol-1 H2) and sluggish kinetics result in a relatively high desorption temperature（>300℃）,which severely restricts widespread applications of MgH2.Nano-structuring has been proven to be an effective strategy that can simultaneously enhance the ab/de-sorption thermodynamic and kinetic properties of MgH2,possibly meeting the demand for rapid hydrogen desorption,economic viability,and effective thermal management in practical applications.Herein,the fundamental theories,recent advances,and practical applications of the nanostructured Mg-based hydrogen storage materials are discussed.The synthetic strategies are classified into four categories:free-standing nano-sized Mg/MgH2 through electrochemical/vapor-transport/ultrasonic methods,nanostructured Mg-based composites via mechanical milling methods,construction of core-shell nano-structured Mg-based composites by chemical reduction approaches,and multi-dimensional nano-sized Mg-based heterostructure by nanoconfinement strategy.Through applying these strategies,near room temperature ab/de-sorption（<100℃） with considerable high capacity（>6 wt%）has been achieved in nano Mg/MgH2 systems.Some perspectives on the future research and development of nanostructured hydrogen storage materials are also provided.