The Effect of Cr2O3/ZnO on Hydrogen Desorption Properties of MgH2. Aep Patah. 1. , Akito Takasaki. 1 and Janusz S. Szmyd. 2. 1. Graduate School of ...
Mater. Res. Soc. Symp. Proc. Vol. 1148 © 2009 Materials Research Society
1148-PP03-38
The Effect of Cr2O3/ZnO on Hydrogen Desorption Properties of MgH2 Aep Patah1, Akito Takasaki1 and Janusz S. Szmyd2 1 Graduate School of Engineering, Shibaura Institute of Technology, 3-7-5 Toyosu, Koto-ku, Tokyo 135-8548, Japan. 2 AGH-University of Science and Technology, Al. Mickiewicza 30, 30-059 Krakow, Poland.
ABSTRACT Some metal oxides, in no doubt, give catalytic effects to improve the kinetics of hydrogen absorption and desorption of magnesium hydride (MgH2) after mechanical milling (MM) process. The addition of oxides has mainly been performed by single oxide such as Nb2O5 or Cr2O3. The effect of addition of more than one oxide at the same time, however, has not been reported yet. We investigated the effects of addition of 1.0 mol% zinc oxide (ZnO) and/or 1.0 mol% Cr2O3 on the hydrogen desorption properties of MgH2. The desorption temperature of hydride were examined by Differential Scanning Calorimeter (DSC) after MM process. The total milling time of MM, performed in an argon gas atmosphere, was 20 hours, and milling speed was 400 rpm. Addition of single oxide separately gave the hydrogen desorption temperature of MgH2 to ~362 °C and to ~360 °C for MgH2/1.0 mol% Cr2O3 and MgH2/1.0 mol% ZnO, respectively. The hydrogen desorption temperature of MgH2 decreased to ~347 °C after combined addition of two kinds of oxides. Most of MgH2-oxide powders showed double hydrogen desorption peaks in DSC curves. Furthermore, after a certain threshold MgH2-oxide composition, the desorption temperature of the peak doublet changed gradually to single peak due to increasing the amount of ZnO. It was also observed by X-ray diffraction measurement (XRD) that the double hydrogen peak corresponded to the presence of two polymorphic forms of magnesium hydride, β- and γ-MgH2. The γ-MgH2 phase is known as a metastable high-pressure phase, produced during MM process. XRD also showed that the presence of ZnO after MM was significantly reduced. Apparently, addition of 1.0 mol% ZnO together with 1.0 mol% Cr2O3 helps to reduce hydrogen desorption temperature of MgH2 by about 30 °C compared to that of MgH2 without any oxide. A synergetic effect is believed to be occurred after addition of two kinds of oxides. Some mechanisms, one of which is thought could be a solid solution reaction of Zn into Mg during heating, could probably decrease the hydrogen desorption temperature of MgH2. ZnO, however, is also thought to act as a catalyst which makes their surfaces available for hydrogen chemisorbed process. The role of both the kind of oxides (Cr2O3/ZnO) and the duality of hydride phases (β- and γ-MgH2) in hydrogen desorption process to help the improvement of absorption/desorption kinetics of MgH2 is also discussed.
INTRODUCTION Magnesium hydride (MgH2) is considered as potential hydrogen storage material because exhibits a high theoretical hydrogen capacity up to 7.6 wt.% and relatively low cost. Nevertheless, practical application of magnesium hydride is limited by slow hydrogen kinetics at low temperature (
