In-situ precipitation of ultrafine Mg₂Ni particles in Mg-Ni-Ag metal fibers and their hydrogen storage properties

The intermetallic compound Mg₂Ni shows improved hydrogen de-/absorption kinetics and a lower desorption temperature compared to pure Mg. However, the coarse Mg₂Ni phase and its limited hydrogenation capacity restrict the application of the Mg₂Ni alloy. In this study, an attempt was made to prepare Mg-Ni alloy fibers with a higher Mg content and a well-distributed Mg₂Ni catalytic phase using the melt extraction (ME) method, and a unique metallic glass fiber was formed. With pre-annealing at 350 °C in a vacuum, uniformly dispersed Mg₂Ni nanoparticles are in-situ formed, the phase transition is revealed to be metallic glass → Mg₆Ni → Mg₂Ni + Mg. About 1.5 wt% of hydrogen can be absorbed by the Mg-Ni fibers at 50 °C, and it is completely released in 8.8 min at 225 °C. Both the JMA and Kissinger models were utilized to accurately characterize the dehydrogenation activation energy, and the values of 90.4 and 95.8 kJ/mol were obtained, respectively. The hydrogen desorption process involves two distinct processes, the decomposition of Mg₂NiH₄ nanoparticles and MgH₂ hydride in sequence, with dehydrogenation enthalpy changes of 64.5 and 78.2 kJ/mol, respectively. After hydrogen absorption and desorption cycles, a loose structure forms around the Mg₂Ni nanoparticles. This structure serves as an efficient nucleation site for hydrides and provides diffusion paths for H atoms.