Catalytic activity of oxides and halides on hydrogen storage of MgH2

Abstract Hydrogen sorption kinetics of ball milled MgH 2 with and without chemical additives were studied. We observed kinetics and capacity improvement with increasing the number of sorption cycles that contributed to the micro/nano cracking of MgH 2 particles, shown by XRD and SEM studies. In addition, to investigate the proposed specific role of O 2− -based additives on the sorption kinetics of MgH 2 , we have undertaken a comparative study evaluating the performances of MgH 2 containing the NbCl 5 , CaF 2 or Nb 2 O 5 additives. At 300 °C, addition of NbCl 5 and CaF 2 improved the sorption capacity to 5.2 and 5.6 wt% within 50 min, respectively, in comparison to the required 80 min in the case of Nb 2 O 5 . This suggests the importance of the chemical nature of the catalyst for hydrogen sorption in MgH 2 . In addition, the catalyst specific surface area was shown to be very critical. High surface area Nb 2 O 5 (200 m 2  g −1 ), prepared by novel precipitation method, exhibits an excellent catalytic activity and helped to desorb 4.5 wt% of hydrogen from MgH 2 within 80 min at a temperature as low as 200 °C.