Excellent catalysis of Mn₃O₄ nanoparticles on the hydrogen storage properties of MgH₂: an experimental and theoretical study

Recently, transition metal oxides have been evidenced to be superior catalysts for improving the hydrogen desorption/absorption performance of MgH₂. In this paper, Mn₃O₄ 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 MgH₂. With the addition of 10 wt% Mn₃O₄ nanoparticles, the MgH₂-Mn₃O₄ composite started to release hydrogen at 200 °C and approximately 6.8 wt% H₂ could be released within 8 min at 300 °C. For absorption, the completely dehydrogenated sample took up 5.0 wt% H₂ within 10 min under 3 MPa hydrogen even at 100 °C. Compared with pristine MgH₂, the activation energy value of absorption for the MgH₂ + 10 wt% Mn₃O₄ composite decreased from 72.5 ± 2.7 to 34.4 ± 0.9 kJ mol⁻¹. The catalytic mechanism of Mn₃O₄ 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 Mn₃O₄. In addition, a cycling test showed that the hydrogen storage capacity and reaction kinetics of MgH₂-Mn₃O₄ could be favourably preserved in 20 cycles, indicative of promising applications as a solid-state hydrogen storage material in a future hydrogen society.