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

Abstract

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, Mg90Ni10Hx, was prepared via a one-step gas–solid process, achieving a well-distributed core–shell microstructure. The as-synthesized Mg90Ni10Hx 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 Mg2NiHx 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.