Synergistic effect of metal chloride-based multiphase on catalyzing rapid hydrolysis of MgH2

Magnesium hydride (MgH 2 ) is a promising solid-state hydrogen carrier due to its high theoretical hydrogen yield and environmentally benign hydrolysis byproducts. However, its practical utilization is severely hindered by sluggish hydrolysis kinetics and low conversion efficiency, which are mainly caused by the rapid formation of a dense Mg(OH) 2 passivation layer. In this study, a low-cost multiphase catalytic system was developed to synergistically accelerate the hydrolysis performance of MgH 2 in seawater. MgH 2 -metal chloride-Na composites were synthesized via high-energy ball milling, and the effects of chloride species (FeCl 3 , CuCl 2 , CoCl 2 , and MgCl 2 ), additive content, milling parameters, and temperature on hydrolysis performance were systematically investigated. Among the studied systems, the MgH 2 -FeCl 3 -Na composite exhibited superior hydrolysis performance, achieving a hydrogen yield of 1560 mL·g −1 (∼99% conversion) within 10 min at 30 °C. The mean hydrogen generation rate reached 393.09 mL·g −1 ·min −1 , which is significantly higher than that of pristine MgH 2 and other chloride-based systems. Kinetic analysis further revealed a markedly reduced apparent activation energy of 25.98 kJ·mol −1 . Microstructural characterization suggests that this enhanced performance originates from a pronounced synergistic effect between FeCl 3 and metallic Na. Specifically, chloride ions induce localized corrosion and effectively disrupt the Mg(OH) 2 passivation layer, while the exothermic reaction between Na and water generates localized heat and modifies the alkaline microenvironment. The synergistic effect dynamically regulates the reaction interface, facilitating the formation of loose, porous Mg(OH) 2 layers that enable sustained hydrolysis. This study highlights the effectiveness of multiphase synergistic catalysts and provides a practical and economical strategy for rapid hydrogen generation from MgH 2 .