Silver electrocrystallization onto carbon electrodes with different surface morphology:: Active sites vs surface features

The influence of the electrode surface quality and surface morphology on the silver electrocrystallization process onto a carbon substrate from 10(-2) M Ag(NH3)(2)(+)/1.6 M NH3-, 1 M KNO3 (pH = 11) electrolyte solution was studied. Three substrates with different types of surface morphology and surface roughness were used: highly oriented pyrolitic graphite (HOPG), mechanically polished vitreous carbon (MPVC), and fractured vitreous carbon (FVC). Before the silver deposition process, the electrode surface was examined and characterized by means of Atomic Force Microscopy (AFM) analysis. Evaluation of the kinetic parameters of the silver nucleation and the growth behavior, as well as other characteristics of the silver electrocrystallization process onto carbon substrates, were based on cyclic voltammetry and chronoamperometric measurements. Cyclic voltammetry data also show that silver deposition efficiency is proportional to the increase of electrode surface roughness (from HOPG, via MPVC to FVC). The silver bulk deposition process on all three carbon substrates was characterized as 3D nucleation and diffusion-controlled growth. However, this process proceeds with different overpotentials on different substrates: the lowest for HOPG and the highest for MPVC electrode surface. The major electrocrystallization parameters, such as nucleation rate, number of active sites, and number of fanned silver nuclei, strictly related to the electrode surface conditions, seem to not follow the same trends as the cyclic voltammetry data. It is clearly indicated in the nonlinear relationship between number of active sites and the surface features (recognized in AFM images). As pointed out in the discussion, it opens new questions regarding the nature of the active sites for deposition on the electrode surface and their identification by microscopic techniques.