Synthesis and functional properties of Mg/MgH2—FeNiCo (Raney type) composite

Abstract

Magnesium hydride (MgH₂) is considered a highly promising material for hydrogen storage and on-demand hydrogen generation due to its high hydrogen capacity, low cost, and environmental safety. However, its practical use, is limited by slow sorption—desorption kinetics and rapid passivation during hydrolysis caused by the formation of a poorly soluble Mg(OH)₂ layer. Mechanochemical hydrogenation is an effective method for producing nanocrystalline MgH₂ with improved reactivity, especially when catalytic additives are introduced to accelerate H₂ dissociation and diffusion. In this work, Mg/MgH₂—FeNiCo composites were synthesized by reactive ball milling in hydrogen with 10 wt. % FeNiCo (Raney type) additive. The FeNiCo catalyst was obtained by alkaline leaching of arc-melted Fe—Ni—Co—Al alloys. Structural analysis (XRD) confirmed the formation of α-MgH₂ and γ-MgH₂ phases, residual Mg and MgO. Microstructure observations showed heterogeneous particle morphology typical of high-energy milling. Hydrogen absorption experiments demonstrated that FeNiCo significantly accelerates magnesium hydrogenation: in 20 h the composite absorbed 5.52 wt. % H, whereas pure Mg reached only 2.43 wt. % under identical conditions. Thermal desorption studies showed that the main peak of hydrogen evolution for the composite occurs at a temperature of 280 °C. The composite was also evaluated as a material for hydrogen generation by hydrolysis. While MgH₂ milled for 20 h released only 3 % hydrogen in distilled water, the Mg/MgH₂ —FeNiCo composite achieved 42 % conversion in –1 90 min. The use of MgCl2 solutions further enhanced performance, increasing conversion up to 81 % at 0.1 mol ∙ L . These results confirm the catalytic efficiency of FeNiCo in both mechanochemical hydrogenation and hydrolysis, demonstrating its potential for efficient in situ hydrogen production.