Local eutectic combined with surface functional treatment: An efficient strategy to lower desorption temperature of bulk magnesium-based hydride

Magnesium-based hydrides are ideal for hydrogen storage, but sluggish dehydrogenation kinetic and relative high operation temperature hindered their practical applications, especially for large particle hydrides. This study reports a novel surface engineering strategy combining local eutectic with functional treatment to substantially improve the desorption behavior of bulk metal hydride. A typical Mg-Ni-based composite, Mg₉₀Ni₁₀H_x, was prepared via a one-step gas–solid process, achieving a well-distributed core–shell microstructure. The as-synthesized Mg₉₀Ni₁₀H_x was subsequently treated with a simple surface functionalization, i.e., short-time hydrolysis. Results showed an exciting improvement in dehydrogenation kinetics: the peak dehydrogenation temperature decreased from 395 °C to 275 °C, and corresponding activation energy decreased from 114.3 to 59.0 kJ/mol H₂, which is comparable to some nanoscaled hydrides with catalysts. Combined with density functional theory calculations, a potential mechanism was proposed: the Mg(OH)₂ generated during hydrolysis can weaken Mg-H bond and induce the dehydrogenation by electrostatic interaction, and hydrogen atoms inside bulk hydrides continue to diffuse to the surface along the microcracks created by volume contraction of Mg₂NiH_x after dehydrogenation, allowing the bulk hydride to continue to dehydrogenate. The results provide alternative strategy to design high-reactive metal hydrides with low cost and extend our understanding of Mg(OH)₂ in magnesium-based hydrides.