Efficient catalysis of FeNiCu-based multi-site alloys on magnesium-hydride for solid-state hydrogen storage

Hydrogen, as a cheap, clean, and cost-effective secondary energy source, performs an essential role in optimizing today's energy structure. Magnesium hydride (MgH2) represents an attractive hydrogen carrier for storage and transportation, however, the kinetic behavior and operating temperature remain undesirable. In this work, a dual-phase multi-site alloy (MsA) anchored on carbon substrates was designed, and its superior catalytic effects on the hydrogen storage properties of MgH2 were reported. Mechanism analysis identified that multi-site FeNi3/NiCu nanoalloys synergistically served as intrinsic drivers for the striking de/hydrogenation performance of the MgH2-MsA systems. Concretely, the unique multi-metallic site structure attached to the surface of MgH2 provided substantial reversible channels and accessible active sites conducive to the adsorption, activation, and nucleation of H atoms. In addition, the coupling system formed by FeNi3 and NiCu dual-phase alloys further enhanced the reactivity between Mg/MgH2 and H atoms. Hence, the onset dehydrogenation temperature of MgH2 + 5 wt% MsA was reduced to 195°C and the hydrogen desorption apparent activation energy was reduced to 83.6 kJ/mol. 5.08 wt% H2 could be released at 250°C in 20 min, reaching a high dehydrogenation rate of 0.254 wt% H2/min, yet that for MgH2 at a higher temperature of 335°C was only 0.145 wt% H2/min. Then, the dehydrogenated MgH2-MsA sample could absorb hydrogen from room temperature (30°C) and charge 3.93 wt% H2 at 100°C within 20 min under 3.0 MPa H2 pressure. Benefiting from carbon substrates, the 5 wt% MsA doped-MgH2 could still maintain 6.36 wt% hydrogen capacity after 20 cycles. In conclusion, this work provides experimental rationale and new insights for the design of efficient catalysts for magnesium-based solid-state hydrogen storage materials.