Production of an Mg/Mg2Ni lamellar composite for generating H2 and the recycling of the post-H2 generation residue to nickel powder

Abstract

The magnesium hydrolyzing reaction was catalyzed in situ using a layered Mg2Ni compound, rapidly producing hydrogen in NaCl solution. The post-H2 generation residue (mixture of Mg(OH)2 and Mg2Ni catalyst) was recycled to recover pure Ni powder from the waste mixture. Pure Mg (153 g) and pure Ni (47 g) in a eutectic composition were easily melted to form a molten alloy by a super-high-frequency (35,000 Hz) induction furnace. The lamellar material had an Mg/Mg2Ni/Mg/Mg2Ni… layered structure, in which each layer was ∼0.8 μm thick; Mg was an anodic phase and Mg2Ni was a cathodic phase (the catalyst). Bulk Mg/Mg2Ni composite alloy contains many microgalvanic cells. Owing to the lamellar microstructure, no dense hydrated oxide film that might have caused surface passivation was found, allowing continuous H2 generation until no magnesium remained to participate in the hydrolysis. The activation energy of the hydrolysis reaction in simulated sea water was ∼36.35 kJ mol−1.