A synchrotron X-ray diffraction study of hydrogen storage and enhanced sorption kinetics in a mini-tank of Mg with crystalline and amorphous catalytic particle additions

Previous work has established that when a few volume percent of transition metal-based particles are dispersed in nano-grained MgH2 powders, H-sorption times are reduced to a few minutes at temperatures near 300 °C. We report H-sorption cycles performed in a mini-tank of Mg powders containing such particle dispersions placed in monochromatised synchrotron light going through the powders for in situ X-ray diffraction in transmission at the European Synchrotron Radiation Facility. The three selected catalyst particle dispersions were Nb2O5, FeF3 and amorphous Ti0.7Ni0.3. The main result is that these very different 2nd phase particle additions have a similar impact on H-sorption in the sense that in all three MgH2 powders, H-sorption goes to completion as T ≈ 270 °C reached during heating. The commonality of the three selected particle dispersions, two crystalline and one amorphous, is that their thermodynamic properties are consistent with the chemical conditions of immiscibility and H-attractive interfaces within MgH2 powders. Once this condition is satisfied, the acceleration of the kinetics of sorption is likely dominated by the extent (specific area) of such internal interfaces.

► We report H-sorption cycles in a mini-tank of Mg powders by in situ XRD using synchrotron light. ► Three selected catalyst particle dispersions were used: Nb2O5, FeF3 and amorphous Ti0.7Ni0.3. ► The three different particle additions have a similar positive impact on H-sorption. ► Sorption times are reduced to a few minutes at temperatures near 260 °C. ► Acceleration of the sorption kinetics is dominated by the extent of internal interfaces.