Catalytic activity of oxides and halides on hydrogen storage of MgH 2

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 2O 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 2O 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 2O 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.