Excellent catalysis of Mn 3 O 4 nanoparticles on the hydrogen storage properties of MgH 2 : an experimental and theoretical study.

Recently, transition metal oxides have been evidenced to be superior catalysts for improving the hydrogen desorption/absorption performance of MgH 2 . In this paper, Mn 3 O 4 nanoparticles with a uniform size of around 10 nm were synthesized by a facile chemical method and then introduced to modify the hydrogen storage properties of MgH 2 . With the addition of 10 wt% Mn 3 O 4 nanoparticles, the MgH 2 -Mn 3 O 4 composite started to release hydrogen at 200 °C and approximately 6.8 wt% H 2 could be released within 8 min at 300 °C. For absorption, the completely dehydrogenated sample took up 5.0 wt% H 2 within 10 min under 3 MPa hydrogen even at 100 °C. Compared with pristine MgH 2 , the activation energy value of absorption for the MgH 2 + 10 wt% Mn 3 O 4 composite decreased from 72.5 ± 2.7 to 34.4 ± 0.9 kJ mol -1 . The catalytic mechanism of Mn 3 O 4 was also explored and discussed with solid evidence from X-ray diffraction (XRD), Transmission Electron Microscope (TEM) and Energy Dispersive X-ray Spectroscopy (EDS) studies. Density functional theory calculations revealed that the Mg-H bonds were elongated and weakened with the doping of Mn 3 O 4 . In addition, a cycling test showed that the hydrogen storage capacity and reaction kinetics of MgH 2 -Mn 3 O 4 could be favourably preserved in 20 cycles, indicative of promising applications as a solid-state hydrogen storage material in a future hydrogen society.