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

Abstract

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 2 Ni 7 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 2 Ni 7 phase, and consequently lowers both the gaseous phase storage and electrochemical discharge capacities. However, Mo also promotes the formation of a Nd 5 Co 19 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.

Properties of Nickel Metal Hydride Battery Using Molybdenum-added Superlattice Metal Hydride Alloy

“…All cells except Cell Mo2 show similar mid-point voltages at different discharge rates ( Figure 4). The increase in mid-point voltage (and the related HRD) in Cell Mo3 is due to the increase in the Nd 5 Co 19 phase abundance, which contributes to a higher reactive surface area [16]. The decrease in HRD of Cell Mo4 and Cell Mo5 are due to their relatively low gaseous phase reversible capacities (second row in Table 1).…”

“…Mn and Co, two other commonly used B-site atoms in the AB 5 MH alloy, were not present in the original superlattice alloy to improve the self-discharge performance [10]. The influence on the hydrogen storage properties (both in the gaseous phase and electrochemistry) by elemental substitutions in Ni in the original formula with other transition metals, such as Mn [13], Fe [14], Co [15], and Mo [16] were reported. The cell performances of the first three substitutions were also evaluated and summarized as follows: Mn improves the HRD by increasing the reactive surface area [17]; Fe extends the cycle life by reducing the Al-leach from the negative electrode [18]; and Co facilitates the low-temperature discharge reaction [19].…”

“…As only the failure modes of Ni/MH batteries made from AB 5 MH alloys were reviewed [20], a summary of failure modes of misch-metal based Ni/MH batteries with different chemical compositions is also included in this paper. The structural, gaseous phase hydrogen storage, and electrochemical properties of these multi-phase superlattice MH alloys previously reported [16] are summarized in Table 1. As the Mo-content in the alloy increased, both the electrochemical capacity and half-cell HRD decreased, and the surface chargetransfer resistance first decreased and then increased.…”