Anodic Polarisation Characterisation of Absorbed Hydrogen in Modified Mm(B5)x Alloys

Abstract

Anodic polarisation curves of Mm(Ni3.6Co0.7Mn0.4Al0.3)x (Mm = mischmetal, 0.85  x  1.15) electrodes were measured under the conditions of various initial concentrations of absorbed hydrogen (H/M), potential sweeping rates (v), temperatures (T), and amounts of reducing agent (y = [NaBH4]) in alkaline solution. Anodic peak current (Ip) at the Mm(B5)x electrodes increased with an increase in T, x and y values. In addition, the Ip value depended linearly on initial hydrogen concentration and square root of potential sweeping rate, irrespective of T, x and y values. Furthermore, the activation energy for hydrogen diffusion decreased with an increase in x and y values. From these results, it is considered that the surface reduction treatment of the Mm(B5)x alloys, performed in alkaline solution with sodium borohydride, the nonstoichiometry and the initial concentration of absorbed hydrogen, are important factors for improving the charge-discharge performance of negative electrodes for metal-hydrogen energy systems.