Enhanced “Hydrogen Pump” Effect in Improving the Hydrogen Storage Performance of MgH ₂ via the Introduction of a Flower-like NiCu Bimetallic MOF

To overcome the hydrogen storage kinetic limitations of magnesium hydride (MgH 2 ), highly effective NiCu bimetallic MOFs with different Ni/Cu ratios were successfully synthesized and introduced into MgH 2 . The Ni 3 Cu 1 MOF, featuring a distinctive flower-like structure assembled from thin nanosheets, demonstrates the most remarkable catalytic activity in enhancing the hydrogen storage properties of MgH 2 . The MgH 2 -8 wt % Ni 3 Cu 1 MOF composite can initiate hydrogen desorption at 198.50 °C and exhibits a significantly reduced dehydrogenation peak temperature of 285.92 °C, in comparison with that of the ball-milled MgH 2 (385.5 °C). This composite can rapidly release 6.18 wt % H 2 at 300 °C and absorb 5.32 wt % H 2 at 150 °C, both within 500 s. The activation energies for dehydrogenation and hydrogenation are reduced to 66.91 and 33.81 kJ/mol H 2, respectively. Furthermore, the MgH 2 -8 wt % Ni 3 Cu 1 MOF presents a capacity retention rate of 93% after 50 cycles, indicating excellent cycle stability. The enhancement in the hydrogen storage performance is mainly attributed to the following two aspects. The distinctive flower-like Ni 3 Cu 1 MOF possesses a relatively large specific surface area, which provides more uniformly dispersed metal active sites and a larger contact area with MgH 2 . Moreover, the Mg 2 Ni(Cu)/Mg 2 Ni(Cu)H 4 phases formed in situ during the initial hydrogen de/absorption cycle act as an enhanced “hydrogen pump” to facilitate the de/hydrogenation process of MgH 2 /Mg. The enhanced effect can be confirmed by theoretical calculations, which reveal a pronounced interfacial electron transfer (0.54 e – ) and a marked elongation of the Mg–H bond (2.85 Å) at the MgH 2 –Mg 2 Ni(Cu) interface compared to that of the MgH 2 –Mg 2 Ni interface. These findings offer a strategy for the design and preparation of bimetallic MOF catalysts to improve the hydrogen storage properties of Mg-based materials.