Electrochemical characterization of nanocrystalline hydrogen storage La1.5Mg0.5Ni6.5Co0.5 alloy covered with amorphous nickel

• Published in: Journal of alloys and compounds Vol. 780; pp. 697 - 704
• Main Authors: Dymek, Martyna, Nowak, Marek, Jurczyk, Mieczysław, Bala, Henryk
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 05-04-2019; Elsevier BV
• Subjects: A. Intermetallics; B. Mechanical alloying; Batteries; C. Electrochemical reactions; Corrosion; Corrosion resistance; Crystals; Densification; Discharge; Electrochemical analysis; Electrode materials; Electrodes; Heat exchange; Heat treatment; Hydrogen; Hydrogen storage materials; Magnetron sputtering; Mechanical alloying; Metal hydrides; Nanocrystals; Nanostructural materials; Nickel coatings; Particulate composites; Protective coatings; Metal hydrides; B. Mechanical alloying; C. Electrochemical reactions; Corrosion; Nanostructural materials; A. Intermetallics
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2018.11.196

Nanocrystalline hydrogen storage La1.5Mg0.5Ni6.5Co0.5 alloy was obtained by mechanical alloying and heat treatment (850 °C/0.5 h). The A2B7 phase is dominant in so synthesized material. Concentration of AB5 phase is close to 3 at. % 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 μm was encapsulated with thin (0.48 μm 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 QNmax). 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.
•Nanocrystalline La1.5Mg0.5Ni6.5Co0.5 hydrogen storage alloy was produced by MA.•Co-addition increases capacity, enhances activation but worsens corrosion resistance.•Co-addition improves hydrogen sorption kinetics and its diffusivity in the alloy.•PVD sputtered, 0.48 μm thick Ni layer inhibits alloy corrosion decay in KOH by 30%.