Electrodeposition of cobalt from citrate containing baths

The kinetics of the initial stages of cobalt electrodeposition on glassy carbon from a chloride bath containing citrate was studied using different electrochemical techniques. Cyclic voltammetry was used to characterize the deposition and the stripping processes. Cobalt films were galvanostatically deposited and potentiodynamically stripped. Complex species distribution in solution functional to the bath composition and pH were used to explain the observed deposition and stripping features. Current transients were analyzed using the models by Scharifker and Hills to describe the general behavior of the nucleation in Cobalt/citrate systems. It was concluded that Co electrodeposition in citrate mediums occurs via an instantaneous nucleation followed by a tridimensional growth under mass control mechanism. It is remarkably different from what other authors have found for Co deposition from solutions with no additive or containing ammonia. Thus, the choice of additive can change the reaction mechanism. Deposition parameters such as number of active sites, critical nucleus size and average diffusivity were estimated.