Morphology-controlled synthesis of cobalt nanostructures by facile electrodeposition: transition from hexagonal nanoplatelets to nanoflakes

- Cobalt nanoplatelets, nanoparticles and nanoflakes are formed by electrodeposition; the influence of concentration, potential and transferred charge on morphology is analyzed;
- Three-dimensional diffusion control cannot justify potentiostatic current transients;
- Aggregative growth can explain the deviation from three-dimensional diffusion control;
- Transition from nanoplatelets to nanoflakes is controlled by pulsed electrodeposition;

Cobalt hexagonal nanoplatelets and cobalt nanoflakes were produced by electrodeposition onto aluminium from cobalt sulphate solutions. The dependence of the nanostructure morphology on cobalt ion concentration and potential was investigated under potentiostatic and pulsed-electrodeposition. Under potentiostatic electrodeposition, cobalt hexagonal nanoplatelets were obtained with cobalt ion concentration equal to 0.01 and 0.1 M, while cobalt hydroxide nanoflakes were formed as the cobalt ion concentration was increased to 0.2 M. Under pulsed electrodeposition, both hexagonal nanoplatelets and hydroxide nanoflakes could be obtained with cobalt ion concentration equal to 0.1 M by modulation of the imposed current/potential wave. The analysis of the current transients recorded under potentiostatic electrodeposition and the microscopic analysis of the deposits indicate that three-dimensional diffusion control cannot adequately describe the growth of the cobalt nanostructures. We propose that an aggregative growth mechanism involving the formation and the surface diffusion of cobalt nanoclusters can explain the influence of electrodeposition parameters on the morphology of the cobalt nanostructures.