Catalytic activity of oxides and halides on hydrogen storage of MgH2

Hydrogen sorption kinetics of ball milled MgH2 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 MgH2 particles, shown by XRD and SEM studies. In addition, to investigate the proposed specific role of O2--based additives on the sorption kinetics of MgH2, we have undertaken a comparative study evaluating the performances of MgH2 containing the NbCl5, CaF2 or Nb2O5 additives. At 300 °C, addition of NbCl5 and CaF2 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 Nb2O5. This suggests the importance of the chemical nature of the catalyst for hydrogen sorption in MgH2. In addition, the catalyst specific surface area was shown to be very critical. High surface area Nb2O5 (200 m2 g-1), prepared by novel precipitation method, exhibits an excellent catalytic activity and helped to desorb 4.5 wt% of hydrogen from MgH2 within 80 min at a temperature as low as 200 °C. © 2006 Elsevier B.V. All rights reserved

Effect of carbon addition on hydrogen storage performances of magnesium-based alloys: From bulk powders to thin films

Mg-bascd thin films were successfully grown by Pulsed Laser Deposition. Dramatic optical changes were observed depending on the conditions of deposition. Films grown in vacuum were shiny metallic whereas the ones grown in a Ar/H2 gas mixture were highly transparent. Ex situ hydrogenation, by annealing the films at 200°C in 15 bars of hydrogen, led to similar metallictransparent transformation. Mg-Cx (x ≤ 20%) films show a faster hydrogenation associated with a significant decrease in oxygen content by carbon addition

Benefits of carbon addition on the hydrogen absorption properties of Mg-based thin films grown by Pulsed Laser Deposition

Mg-Ni thin films were grown using Pulsed Laser Deposition. In situ optical changes from shiny metallic to transparent states were observed for films deposited in vacuum and under an Ar/H2 gas mixture (93/7%), respectively. Optical changes were also achieved by ex situ hydrogenation under hydrogen gas pressure of 15 bars at 200 °C. However, after ex situ hydrogenation, the optical transmittance of the Mg-based hydrogenated thin films did not exceed 25%. Such limitation was attributed to oxygen contamination, as deduced by High Resolution Transmission Electron Microscopy observations, showing the co-existence of both Mg-based and MgO phases for as-deposited films. A significant decrease in oxygen contamination was successfully achieved with the addition of carbon, leading to the preparation of (Mg-based)-Cx (x < 20%) thin films showing a faster and easier hydrogenation. © 2006 Elsevier B.V. All rights reserved