Effects of Molybdenum to the Hydrogen Storage and Electrochemical Properties of Superlattice Metal Hydride Alloy

Abstract

The structure, gaseous phase, and electrochemical hydrogen storage properties of a series of superlattice metal hydride alloys with nominal compositions Mm 0.83Mg0.17Ni2.94‒xAl0.17Co0.20Mox, where Mm is a mixture of La, Pr, and Nd and x = 0.00, 0.05, 0.10, 0.15, and 0.20, prepared by induction melting method were studied. The Mo segregates out of the main phase to form a metallic secondary phase, leading to a larger reactive surface area. The unit cell of the main Nd 2Ni7 increases with an increase in Mo-content through changes in both phase composition and abundance. The addition of Mo reduces the abundance of the main Nd 2Ni7 phase, and consequently lowers both the gaseous phase storage and electrochemical discharge capacities. However, Mo also promotes the formation of a Nd 5Co19 phase, which contributes to a higher surface reactive area at both room temperature and −40°C. A 1.1 at% of Mo partially replacing Ni is recommended for improvement in low-temperature performance without sacrificing the discharge capacities and high-rate dischargeability owing to the improvement in the surface catalytic ability. In addition, the effects of Mo substitutions to the electrochemical properties of the superlattice alloy are also compared to those from other substitutions, such as Mn, Fe, and Co.