| Summary: | ZnO nanoparticles in a spherical-like structure were synthesized via filtration and calcination methods, and different amounts of ZnO nanoparticles were added to MgH<sub>2</sub> via ball milling. The SEM images revealed that the size of the composites was about 2 μm. The composites of different states were composed of large particles with small particles covering them. After the absorption and desorption cycle, the phase of composites changed. The MgH<sub>2</sub>-2.5 wt% ZnO composite reveals excellent performance among the three samples. The results show that the MgH<sub>2</sub>-2.5 wt% ZnO sample can swiftly absorb 3.77 wt% H<sub>2</sub> in 20 min at 523 K and even at 473 K for 1 h can absorb 1.91 wt% H<sub>2</sub>. Meanwhile, the sample of MgH<sub>2</sub>-2.5 wt% ZnO can release 5.05 wt% H<sub>2</sub> at 573 K within 30 min. Furthermore, the activation energies (E<sub>a</sub>) of hydrogen absorption and desorption of the MgH<sub>2</sub>-2.5 wt% ZnO composite are 72.00 and 107.58 KJ/mol H<sub>2</sub>, respectively. This work reveals that the phase changes and the catalytic action of MgH<sub>2</sub> in the cycle after the addition of ZnO, and the facile synthesis of the ZnO can provide direction for the better synthesis of catalyst materials.
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