Selective NdH2 exposure enhances hydrogen storage capability of Mg-Mg2Ni nanocomposites over 3700 cycles

Despite the development of Mg-based hydrogen storage alloys over decades, undesired particle growth and poorly controlled interfacial connectivity have remained unsolved, significantly degrading their hydrogen storage capability. These challenges majorly arise from the uniformly dispersed multiple phases of alloys. Here, we report that the NdH2 exposed Mg-Mg2Ni nanocomposite (NdH2@Mg-Mg2Ni), realized via a scalable hot-extrusion and hydrogen-induced in-situ decomposition, can address the above-mentioned issues. In it, Mg serves as hydrogen storage phase while NdH2 and Mg2Ni serve as catalytically active sites for hydrogen dissociation, diffusion, and nucleation, respectively. In addition, the surface exposed NdH2 nanoparticles serve as the pinning center, not only ensuring the Mg-Mg2Ni interfacial connection but also avoiding the direct contact of each particle. Consequently, NdH2@Mg-Mg2Ni enables one of the lowest hydrogen release temperatures (176.2 °C) among the Mg-based alloys, releasing 5.1 wt.% H2 even at 180 °C. Thanks to the selective NdH2 exposure, NdH2@Mg-Mg2Ni exhibits an exceptional chemical and morphological stability, enabling robust hydrogen storage capability over 3700 cycles. The present study proposes a facile and scalable approach to optimize multiple-phase morphology and chemical properties of Mg-based hydrogen storage materials. Selective exposure of NdH2 exhibits bifunctional impacts on improving reaction kinetics and chemical/morphological robustness. It enabled reversible hydrogen storage capability at 180 °C which can be cycled for >3700 times.