Hydrogen sorption improvement of MgH2 catalyzed by CeO2 nanopowder

Abstract

In this study, we investigate the effects of the addition of CeO2 nanopowder on the hydrogen storage properties of MgH2. The 5-wt% CeO2-added MgH2 sample showed improvement in the hydrogenation rate compared with pristine MgH2, with the CeO2-added MgH2 sample releasing about 3.6-wt% hydrogen within 30 min at 320 °C whereas the as-received MgH2 released less than 1.0-wt% hydrogen under the same conditions. Additionally, with respect to absorption kinetics, the total hydrogen absorption capacity of the MgH2 + 5-wt% CeO2 composite increased from 3.5 wt% to 3.8 wt% in 10 min at 320 °C. From a Kissinger plot of the differential scanning calorimetry at different heating rates, the apparent activation energy was determined to be 133.62 kJ/mol for the as-milled MgH2 and 108.65 kJ/mol for the 5-wt% CeO2-added MgH2. This indicates that adding CeO2 nanopowder decreases the activation energy for the hydrogen desorption of MgH2. The formation of new phases of CeH2 by the doping of CeO2 nanopowder with MgH2 after the dehydrogenation and rehydrogenation processes was observed in the X-ray diffraction spectra. It is believed that the enhancement of the hydrogenation performance of the MgH2/CeO2 composite is due to combination of the CeH2 active species and CeO2 itself.