Influence of co-milling with palladium black on hydrogen sorption performance and poisoning tolerance of surface modified AB5-type hydrogen storage alloy

Abstract

This work is focused on the effect of Pd introduction into AB5-type hydrogen storage alloy through ball milling, in combination with conventional electroless plating technique, on hydrogen sorption performance and poisoning tolerance of the material. The AB5 substrate alloy was milled with small (0–5 wt%) amounts of Pd black. The effect of co-milling of the AB5 substrate with Pd on structure/phase composition, morphology, and hydrogen storage performance of the material was investigated.It was shown that co-milling of the AB5-type alloy powder with ≤1 wt% of Pd black does not result in the improvement of the material activation performance and poisoning tolerance while increasing Pd additive content produced insignificant improvements. At the same time, ball milled samples, further subjected to a standard procedure of electroless autocatalytic deposition of Pd, exhibited similar (co-milling with <1 wt% Pd) or better (co-milling with ≥1 wt% Pd) hydrogen uptake kinetic performances at lower Pd surface loading as compared to the non-milled AB5 alloy powder plated with Pd at similar conditions. The observed features were credited to the higher specific surface area of the ball milled material where Pd species introduced in the course of the ball milling played a role as nucleation centres during subsequent deposition of Pd. Conversely, the Pd-plated material obtained by co-milling of AB5 with >2 wt% of Pd black exhibited lower maximum hydrogen sorption capacities, as compared to the non-milled surface modified reference material. The most probable reason for that is in the distortion and disproportionation of the parent structure of the AB5 substrate during its co-milling with Pd black.