The interaction of hydrogen with oxidic promoters of hydrogen storage in magnesium hydride

The present work is devoted to monitor the reactivity with hydrogen of various oxide systems (Nb₂O₅, WO₃ and a mixed Mg/Nb/O oxide) in the aim of understanding the role of oxides as promoters for hydrogen storage in MgH₂. The reactivity of the oxides has been tested using either molecular hydrogen or “nascent” hydrogen produced by reaction of zinc with hydrochloric acid. Thermal desorption-mass spectrometry experiments indicate that hydrogen adsorbed in Nb₂O₅ and Mg/Nb/O mixed oxides is, in part, reversibly released and, for a second fraction, released as water. By contrast, water is the only product desorbed by WO₃ after contact with hydrogen. This could explain the higher performances of Nb₂O₅ as kinetic promoter of hydrogen storage in comparison with WO₃.