Metal organic framework supported niobium pentoxide nanoparticles with exceptional catalytic effect on hydrogen storage behavior of MgH2

Abstract

Nb2O5 nanoparticles with an average particle size of 10 nm supported on a rhombic dodecahedral metal organic framework (MOF) were successfully synthesized by a facile one-pot hydrothermal reaction and subsequent calcination process. Experimental results demonstrated that the prepared catalyst drastically improved the hydrogen storage behavior of MgH2. 7 wt% Nb2O5@MOF doped MgH2 started to desorb hydrogen at 181.9 °C and 6.2 wt% hydrogen could be released within 2.6 min and 6.3 min at 275 °C and 250 °C, respectively. The fully dehydrogenated composite also displayed excellent hydrogenation by decreasing the onset absorption temperature to 25 °C and taking up 4.9 wt% and 6.5 wt% hydrogen within 6 min at 175 °C and 150 °C, respectively. Moreover, the corresponding activation energy was calculated to be 75.57 ± 4.16 kJ mol−1 for desorption reaction and 51.38 ± 1.09 kJ mol−1 for absorption reaction. After 20 cycles, 0.5 wt% hydrogen capacity was lost for the MgH2+7 wt% Nb2O5@MOF composite, much lower than 1.5 wt% of the MgH2+7 wt% Nb2O5 composite. However, the addition of Nb2O5@MOF had limited effect on reducing the dehydrogenation enthalpy of MgH2. Microstructure analysis revealed that Nb2O5 particles were uniformly distributed on surface of the MgH2 matrix and synergistically improved the hydrogen storage property of MgH2 with MOF.

Keywords

• Hydrogen storage
• MgH2
• Nb2O5@MOF
• Reversibility
• Catalytic mechanism