Direct observations of diffusion controlled microstructure transition in Mg-In/Mg-Ag ultrafine particles with enhanced hydrogen storage and hydrolysis properties

In this work, Mg(In) and Mg(Ag) solid-solution ultrafine particles were successfully synthesized by using a direct current (DC) arc-plasma method and their hydrogen storage and hydrolysis behaviors were thoroughly investigated. In particular, microstructural analyses clearly reveal that MgH 2 @MgIn and MgH 2 @MgAg composites are autogenerated upon hydrogenation via the formation of nano MgIn or MgAg intermetallic phase on MgH 2 : Mg(In/Ag) + H 2  ⟷ MgH 2  + MgIn/MgAg. Upon dehydrogenation, in-situ TEM observations confirm that the reverse reaction occurs through the diffusion of In/Ag from the MgIn/MgAg phase to MgH 2 . Such a diffusion process is coupled with the decomposition of MgH 2 , leading to the microstructural transition from MgH 2 @MgIn or MgH 2 @MgAg to corresponding solid solutions. For Mg-In system, the discovery of the intermediate phase Mg 3 In through in-situ TEM observation indicates that the dehydrogenation process is a two-step reaction dominated by the diffusion of In. Meantime, the improved hydrolysis performances of the MgH 2 @MgIn and MgH 2 @MgAg composites are primarily attributed to the direct participation of MgIn/MgAg in the hydrolysis reaction, providing more active sites for accelerating hydrogen yield. Therefore, the introduction of In or Ag into Mg has provided with noticeable improvements in the hydrogen storage as well as the hydrolysis properties of MgH 2 .