MnFe2O4 nanopowder synthesised via a simple hydrothermal method for promoting hydrogen sorption from MgH2

The effects of MnFe2O4 nanopowder synthesised via a simple 'hydrothermal' method on the hydrogen storage properties of MgH2 are investigated for the first time. The particle size of the as-synthesised MnFe2O4 nanoparticles is determined to be about 10 nm. We observe that MnFe2O4 catalyst decreases the decomposition temperature of MgH2 and enhances the sorption kinetics. Interestingly, the onset hydrogen desorption temperature of 10 wt% MnFe2O4-doped MgH2 sample gets lowered from 350 °C to 240 °C with faster kinetics, and the sample shows an average dehydrogenation rate 8-9 times faster than that of the as-milled MgH2 sample. By adding 10 wt% of as-prepared MnFe2O4 to MgH2, approximately 5.5 wt% hydrogen can be absorbed in 10 min at 200 °C. In contrast, the un-doped MgH2 sample absorbed only 4.0 wt% hydrogen in the same period of time. From the Kissinger analysis, the apparent activation energy for hydrogen released in the MnFe2O4-added MgH2 composite is found to be 108.42 kJ/mol, which is much lower than the activation energy for hydrogen released in the as-milled MgH2 (146.57 kJ/mol). It is believed that the in situ formed Fe particle and Mn-containing phases together play a synergistic role in remarkably improving MgH2 storage properties.