Characterizing hydrogen storage behavior of Mg-based materials catalyzed by S2− and O2− ions

Abstract

Composites of Mg90Ce5Y5 + 5.0 wt % MoS2/MoO2 were produced by vacuum refining technology. The phase-composition and microstructure of the specimens were analyzed using X-ray diffraction, transmission electron microscopy, electron diffraction, and inductively coupled plasma optical emission spectrometry. The performance of hydrogen storage was analyzed using thermogravimetric and differential thermal analysis curves and a semi-automatic Sievert-type device. The results indicated that the catalytic MoS2 as a single phase was uniformly distributed in the matrix. However, the doping of MoO2 introduced O2− ions, which combined with Mg and Ce to form MgO and CeO2 phases, respectively. The MoS2-catalyzed alloy exhibited faster hydrogen absorption and desorption rates, which could absorb 4.5 wt % H2 in 120 s (at 573 K) and release 3 wt % H2 in 330 s (at 633 K). The initial dehydrogenation temperatures of the MoS2- and MoO2-catalyzed alloys were 467.7 and 475.7 K, respectively. The dehydrogenation activation energy of MoS2- and MoO2-catalyzed alloys were 103.7 and 110.2 kJ mol−1 respectively. Addition of MoO2 and MoS2 modified the decomposition enthalpy and entropy values, but these changes were very limited. Generally, S2− was superior to O2− ions in enhancing the hydrogen storage properties of the alloy.