A study of the ZrF4, NbF5, TaF5, and TiCl3 influences on the MgH2 sorption properties

Magnesium hydride with 7 wt.% of various metal halide additives (ZrF4, TaF5, NbF5 and TiCl3) were ball milled, and the influence of these dopants on the kinetics of absorption and desorption was studied. The pressure–composition–temperature isotherms (P–C–T) measured by Sieverts’ apparatus did not show thermodynamic changes in the studied materials. Moreover, XPS studies demonstrated that the metal halides used in this study (except ZrF4) took part in the partial and full disproportionation reactions directly after milling and the first desorption/absorption cycle. The catalytic effect of metal halides on the Mg hydrogenation/dehydrogenation process was caused by the formation of pure transition metal and/or the MgF2 phase, which led to the influence of two simultaneous factors on the sorption properties of the MgH2.

► The ZrF4 and NbF5 halide additives could significantly influence the sorption properties of MgH2.
► The metal halides have a catalytic influence on the absorption/desorption kinetics.
► The catalytic efficiency is related to the coexistence of various forms of fluorides/chlorides.