Remarkable low-temperature hydrogen cycling kinetics of Mg enabled by VH_(x) nanoparticles

Nanoscaled catalysts have attracted much more attention due to their more abundant active sites and better dispersion than their bulky counterparts.In this work,VH_(x) nanoparticles smaller than 10 nm in average size are successfully synthesized by a simple solid-state ball milling coupled with THF washing process,which are proved to be highly effective in enhancing the hydrogen absorption/desorption kinetics of MgH_(2) at moderate temperatures.The nano-VH_(x)-modified MgH_(2) releases hydrogen from 182℃,which is 88℃ lower than additive-free MgH_(2).The release of hydrogen amounts to 6.3 wt%H within 10 min at 230℃ and 5.6 wt%H after 30 min at 215℃ with initial vacuum.More importantly,the dehydro-genated MgH_(2)+10 wt.%nano-VH_(x) rapidly absorbs 5.2 wt%H within 3 min at 50℃ under 50 bar H_(2).It even takes up 4.3 wt%H within 30 min at room temperature(25℃)under 10 bar H_(2),exhibiting supe-rior hydrogenation kinetics to most of the previous reports.Mechanistic analyzes disclose the reversible transformation between V and V-H species during the hydrogen desorption-absorption process.The ho-mogeneously distributed V-based species is believed to act as hydrogen pump and nucleation sites for MgH_(2) and Mg,respectively,thus triggering fast hydrogenation/dehydrogenation kinetics.