Catalytic effect of in situ formed Mg2Ni and REHx (RE: Ce and Y) on thermodynamics and kinetics of Mg-RE-Ni hydrogen storage alloy

Abstract To clarify the effect of Mg2Ni and REHx (RE: Ce and Y) on the thermodynamics and kinetics of Mg-RE-Ni alloys, a series of quaternary Mg–Ce–Y–Ni alloys with different RE and Ni contents were prepared by vacuum induction melting. Their microstructure, phase composition, and the hydrogen storage performance were investigated by using X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and Sievert’s-type apparatus. The results indicate that the alloys are mainly composed of the REMgx phase, Mg2Ni phase, and Mg phase, and the change of RE and Ni contents did not change the phase composition but affected the phase content and micro-eutectic morphology. After hydrogenation, the REMgx phase was decomposed into irreversible REHx grains and dispersed in the MgH2 matrix together with Mg2NiH4 grains, which result in an outstanding kinetics performance. By contrast, the REHx phase is more favorable for hydrogen absorption, while Mg2NiH4 is more favorable for hydrogen desorption, which attributes to their independent catalytic mechanisms. Also, the finer microstructure induced a slight decrease in thermodynamics. The Ni5 alloy has an optimal comprehensive hydrogen storage performance, which can absorb 5 wt% H2 within 2 min and release the same amount of hydrogen at 300 °C within 10 min.