Mechanical Pre-defect Engineering Promotes One-Step Synthesis of MgH2

Abstract

Magnesium hydride (MgH₂) is a promising hydrogen storage material with a high storage capacity. However, its current commercial price of up to US$ 700 kg^–1 severely limits its engineering applications. Ball milling, characterized by low energy consumption and high efficiency, offers considerable potential for substantially reducing the production cost of MgH₂. Nevertheless, this method suffers from an intrinsic self-limiting effect: the MgH₂ product shell mechanically shields the underlying Mg from external energy input and impedes hydrogen diffusion into the unreacted Mg core, resulting in products with low purity. Herein, a mechanical pre-defect engineering strategy is proposed. Based on Hertzian contact theory, high-modulus SiC nanoparticles are employed to amplify localized stress and induce vacancies and dislocations within the Mg matrix. Together, ab initio molecular dynamics (AIMD) simulations, density functional theory (DFT) calculations, finite-element simulations, and multiscale characterizations reveal that the SiC-induced defect network promotes H migration through strain- and vacancy-mediated pathways, thereby overcoming the mechanical shielding imposed by the MgH₂ shell. Consequently, MgH₂ with a hydrogen storage capacity of 7.4 wt % is synthesized in one step at a mild ball-milling speed of 200 rpm without heat treatment. Moreover, its hydrogen desorption peak temperature is reduced to 347 °C, which is 111 °C lower than that of commercial MgH₂. This work provides a novel pathway for the low-cost and efficient synthesis of MgH₂.