TY - GEN
T1 - The effect of Cr2O3/ZnO on hydrogen desorption properties of MgH2
AU - Patah, Aep
AU - Takasaki, Akito
AU - Szmyd, Janusz S.
PY - 2008/12/1
Y1 - 2008/12/1
N2 - Some metal oxides, in no doubt, give catalytic effects to improve the kinetics of hydrogen absorption and desorption of magnesium hydride (MgH 2) after mechanical milling (MM) process. The addition of oxides has mainly been performed by single oxide such as Nb2Os or Cr 2O3. 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% Cr2O 3 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 MgH 2 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 MgH 2 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 (Cr 2O3/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.
AB - Some metal oxides, in no doubt, give catalytic effects to improve the kinetics of hydrogen absorption and desorption of magnesium hydride (MgH 2) after mechanical milling (MM) process. The addition of oxides has mainly been performed by single oxide such as Nb2Os or Cr 2O3. 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% Cr2O 3 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 MgH 2 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 MgH 2 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 (Cr 2O3/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.
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M3 - Conference contribution
AN - SCOPUS:77950492286
SN - 9781615677740
T3 - Materials Research Society Symposium Proceedings
SP - 190
EP - 195
BT - Solid-State Chemistry of Inorganic Materials VII
T2 - 2008 MRS Fall Meeting
Y2 - 1 December 2008 through 5 December 2008
ER -