Effects of substitution with foreign metals on the crystallographic, thermodynamic and electrochemical properties of AB 5-type hydrogen storage alloys

Abstract

Effects of substitution with foreign metals on the crystallographic, thermodynamic and electrochemical properties of AB 5-type hydrogen storage alloys were investigated. The unit cell volume of MmNi 5 − x Al x ( Mm = mischmetal, 0.2 ⩽ x ⩽ 1.0) alloys and the values of enthalpy change (−ΔH) in hydride formation increased monotonously with an increase in x-value, but the discharge capacity and high-rate dischargeability had a limiting value. For the MmNi 4.2Al 0.4M 0.4 ( M = Cr, Mn, Fe, Co) alloys, both the unit cell volume and the −ΔH value increased with increasing metallic bond radius of the foreign metal. Especially, manganese improved the discharge capacity and the high-rate dischargeability.