Modulated noble metal/2D MOF heterostructures for improved hydrogen storage of MgH ₂

Abstract

Abstract The conjugation of external species with two‐dimensional (2D) materials has broad application prospects. In this study, we have explored the potential of noble metal/2D MOF heterostructures in hydrogen storage. Specifically, the MgH 2 ‐Ni‐MOF@Pd system has shown remarkable hydrogen desorption/sorption performances, starting to liberate hydrogen at 181 °C, which is 230 °C lower than that of pristine MgH 2 . Under the catalytic effect of Ni‐MOF@Pd, the dehydrogenation apparent activation energy of MgH 2 is noticeably decreased from (133.5 ± 17.5) to (34.58 ± 1.87) kJ·mol −1 , and the hydrogenation apparent activation energy is reduced from (70.41 ± 7.43) to (25.78 ± 4.64) kJ·mol −1 , which is lowered by 63.4%. The fully‐dehydrogenated MgH 2 ‐Ni‐MOF@Pd composite rapidly uptakes hydrogen, with 2.62 wt% at 100 °C and 6.06 wt% at 150 °C within 300 s, respectively. The mechanism analysis of MgH 2 catalyzed by Ni‐MOF@Pd has revealed that the transformation of Mg 2 Ni and Mg 2 NiH 4 could act as a “hydrogen pump”, providing numerous channels for fast diffusion and transport of hydrogen atoms. Moreover, in the dehydrogenation process, the element Pd reacts with MgH 2 to form the Mg‐Pd alloy phase, which makes MgH 2 take precedence to decompose through the Mg‐Pd alloy rather than self‐decomposition, further reducing thermal stability and improving de/hydrogenation kinetics. The synergistic effect of Mg‐Pd, Mg 2 Ni, and the special ultra‐thin 2D sheet structure of the additive is the main reason for the good hydrogen storage property of MgH 2 ‐Ni‐MOF@Pd. Our findings provide inspiration for designing efficient multi‐functional additives with unique morphologies to optimize the hydrogen desorption/sorption behaviors of hydrogen storage materials.