Journal of Alloys and Compounds | 2019
Electrochemical characterization of nanocrystalline hydrogen storage La1.5Mg0.5Ni6.5Co0.5 alloy covered with amorphous nickel
Abstract
Abstract Nanocrystalline hydrogen storage La1.5Mg0.5Ni6.5Co0.5 alloy was obtained by mechanical alloying and heat treatment (850\u202f°C/0.5\u202fh). The A2B7 phase is dominant in so synthesized material. Concentration of AB5 phase is close to 3\u202fat. % and is 2.6 times lower than that in Co-free La1.5Mg0.5Ni7 alloy. The La1.5Mg0.5Ni6.5Co0.5 powder fraction of 20–50\u202fμm was encapsulated with thin (0.48\u202fμm thick), amorphous nickel by magnetron sputtering. The electrochemical charge/discharge multicycling of powder composite electrodes was carried out in view of material potential usefulness as electrode material for Ni/MHx batteries. Partial substitution of Ni by Co in La1.5Mg0.5Ni7 nanocrystalline alloy is prone to increase of electrode discharge capacity (up to 14%) and enhances its activation (strong decrease of Nmax cycle and simultaneous increase of Q N max ). On the other hand, Co addition worsens corrosion degradation behavior, but the corrosion resistance can be improved (≈30%) by the application of amorphous nickel coating. Finally, Co modified La1.5Mg0.5Ni7 nanocrystalline alloy reveals 15% greater exchange current density of H2O/H2 system and improved hydrogen diffusivity compared to the reference, nanocrystalline Co-free La1.5Mg0.5Ni7 hydrogen storage material.