Ultra-Small MgH2 Nanoparticles Embedded Into an Ordered Microporous Carbon Showing Rapid Hydrogen Sorption Kinetics

Abstract

MgH2 nanoparticles with different average sizes have been prepared into an ordered microporous carbon by tuning the Mg amount from 15 to 50 wt%. Ultra-small particles with mean size of 1.3 and 3.0 nm have been obtained for 15 and 25wt% Mg content, respectively. The hydrogen desorption properties strongly depend on the nanoparticle size, as evidenced by different thermal analysis techniques. The onset temperature of hydrogen desorption for MgH2 nanoparticles below 3 nm occurs at temperature about 245 K lower than microcrystalline material. Two distinct hydrogen desorption peaks are noticed for nanoparticles with mean size of 1.3 and 3.0 nm, as confirmed by TDS and HP-DSC. 1H NMR investigations suggest the presence of two MgH2 populations with enhanced hydrogen mobility, as compared to the microcrystalline hydride. The short hydrogen diffusion path and the enhanced hydrogen mobility may explain the increased desorption kinetics of these ultra-small nanoparticles.