The optimized hydrogen storage properties of the RE-Mg-based alloys by adding Ba

The inherent drawbacks of sluggish kinetics and excessive thermodynamic stability limit the practical deployment of Mg-based hydrogen storage materials. In this study, multi-component Mg90La2Ce2Ni3Al3-xBax (x = 0, 0.3, 0.6, 0.9, 1.2) alloys were fabricated. X-ray diffraction analyses reveal that Ba-containing alloys develop a multi-phase structure comprising Mg, La2Mg17, CeMg12, AlNi, and the Mg17Ba2 phase. The Mg17Ba2 induces a reversible transformation between Ba2Mg7H18 and Ba2MgH6, which occurs alongside the primary hydrogenation and dehydrogenation reactions of MgH2 and Mg. Importantly, the generated LaH3, CeH2.73, and Ba2Mg7H18/Ba2MgH6 hydrides, in conjunction with the AlNi phase, introduce numerous phase boundaries within the alloys. This structural change creates numerous nucleation sites for MgH2/Mg and diffusion channels for hydrogen atoms. Consequently, the activation and hydrogen absorption and desorption properties of the alloys are significantly enhanced. Kinetic analysis using the Johnson-Mehl-Avrami-Kolmogorov model demonstrates that Ba doping accelerates the growth of MgH2 and facilitates the diffusion of hydrogen atoms during hydrogenation. Furthermore, both the calculated dehydrogenation activation energy and the peak dehydrogenation temperature of the alloys significantly decrease with the introduction of Ba element, confirming its pivotal role in enhancing the performance of Mg-based alloys.