Discharging characteristics of CoB nano powders

CoB nano powders, which are considered as prospective anode material for the secondary nickel batteries, were synthesized by the chemical reduction method and their charge/discharge cyclic characteristics were investigated. The effect of heat-treatment on the structure and the discharging behavior of CoB alloy was also investigated. It was observed that the amorphous/nano-crystalline CoB had very limited hydrogen storage capacity and the crystallized CoB had no hydrogen adsorption ability at all. The big portion of boron present in CoB alloy dissolved selectively into 6 M KOH solution in the first discharge process. After selective dissolution of boron even the amorphous/nano-crystalline CoB alloy lost its hydrogen adsorption ability. The initial discharge capacity of CoB alloy increased as the boron content of CoB alloy increased since the oxidation of boron contributed to (created complication in) the initial discharge process of CoB alloy. After initial charge/discharge process all the subsequent charge/discharge processes were controlled totally by the perfectly reversible Co oxidation/reduction reactions which took place more efficiently in the crystallized structures. So this study makes important contribution to the resolution of the disagreement in the literature that CoB cannot be considered as the hydrogen storage alloy.

► Crystallized CoB structure had no hydrogen adsorption ability at all.
► Boron present in CoB alloy dissolved selectively during the first discharge.
► The initial discharge capacity of CoB increased as the B content of CoB increased.
► Oxidation/reduction reactions took place more efficiently in the crystallized CoB.