Improvement in the electrochemical properties of ZrMn2 hydrides by substitution of elements

Abstract

The hydrogen-storage properties and the electrochemical properties are investigated for the alloys ZrMn 2 Ni x , ZrMnNi 1+x , Zr 0.5 Ti 0.5 Mn 0.4 V 0.6 Ni 1-x Fe x and Zr 0.5 Ti 0.5 Mn 0.4 V 0.6 Ni 0.85 M 0.15 . The C14 Laves phase forms in all the alloys ZrMn 2 Ni x (x=0.0, 0.3, 0.6, 0.9 and 1.2). Among the alloys ZrMn 2 Ni x , ZrMn 2 Ni 0.6 has the largest discharge capacity (29 mAh/g) and a relatively good cycling performance, and shows a relatively easy activation. The C14 Laves phase also forms in all the alloys ZrMnNi 1+x (x=0.0, 0.1, 0.2, 0.3 and 0.4). Among the alloys ZrMnNi 1+x , ZrMnNi 1.0 has the largest discharge capacity (42 mAh/g) and a relatively good cycling performance, and shows the easiest activation. Zr 0.5 Ti 0.5 Mn 0.4 V 0.6 Ni 1-x Fe x (x=0.00, 0.15, 0.30, 0.45 and 0.60) has the C14 Laves phase hexagonal structure. Their hydrogen storage capacities do not show significant differences. The discharge capacity just after activation decreases with an increase in the amount of the substituted Fe but the cycling performance is improved. The discharge capacity after activation of the alloy with x=0.00 is about 240 mAh/g at the current density 60 mA/g.

C14 Laves Phase Metal Hydride Alloys for Ni/MH Batteries Applications

“…The cycle stability improvement of C14 MH alloy using Mo was also reported [42]. However, reports on the negative impact of Mo on the capacity, cycle life, and activation of C14 MH alloy are also available, presumably due to lack of Cr or Co in the composition [197,199]. Partially replacing Cr with Mo increases the gaseous phase H-storage capacity [210,211], ease of activation, and HRD [212].…”

“…However, reports also suggest that Fe contributes to a low capacity [42] and higher cycle life [196,197]. In a V-free C14 alloy, the addition of Fe improves low-temperature performance, but hinders cycle life and charge retention [144].…”

Improvement in the low-temperature performance of AB5 metal hydride alloys by Fe-addition

“…Charge retention of the Fe-containing alloys is slightly worse than the Fefree base alloy, as the Fe dissolves into the electrolyte during cycling [66,68]. The multi-valence property of the Fe-ion may contribute to the oxidation-reduction shuttling effect between the positive and negative electrodes thus lowering charge retention.…”

“…Therefore, the increase in the half-cell HRD is mainly due to the improvement of the surface reaction and is not related to the bulk diffusion of hydrogen. In a Fe-containing AB 2 MH alloy, an Ferich surface is formed after activation and is believed to contribute positively to the surface reaction [66].…”

Fe-Substitution for Ni in Misch Metal-Based Superlattice Hydrogen Absorbing Alloys—Part 1. Structural, Hydrogen Storage, and Electrochemical Properties

“…Fe has been used as a low-cost supplement in AB 2 [15][16][17][18][19][20][21][22], AB 5 [23][24][25][26][27][28][29][30][31][32][33][34], and body-centered-cubic (bcc) [35][36][37][38][39][40] HAAs. However, the results of Fe incorporation in these HAAs have so far been inconsistent.…”