Kinetics and Thermodynamics of Metal Cluster Nucleation Over Graphene Oxide

An assessment of nucleation and growth mechanism of tin and cobalt over graphene oxide (GO) substrate is performed using the cyclic voltammetry (CV) and chronoamperometry (CA) techniques. The CV tests revealed that deposition of tin and cobalt on GO is an irreversible and diffusion-controlled process. From the CA tests, it was deduced that the deposition process involved the formation of adatom layer at the substrate-electrolyte interface prior to nucleation and growth. Proton reduction reaction over the deposited metal nuclei also took place simultaneously with three-dimensional diffusion-controlled nucleation and growth. While the deposition mechanism for both metals exhibits similarity, the kinetic parameters like nucleation rate constant (A) and number density of active nucleation sites (N₀) varied tremendously for both metals. Application of classical and atomistic theory of nucleation revealed that the Gibb’s free energy required for the formation of critical nucleus for Sn and Co deposition was comparable to room temperature thermal energy and the size of supercritical nucleus is one atom. This meant that under the experimental conditions of deposition, every Sn and Co atom that deposited over GO is a supercritical nucleus that can grow irreversibly.