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 th e 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 st udied. Three substrates with different types of surface morphology and surf ace roughness were used: highly oriented pyrolitic graphite (HOPG), mechani cally polished vitreous carbon (MPVC), and fractured vitreous carbon (FVC). Before the silver deposition process, the electrode surface was examined a nd characterized by means of Atomic Force Microscopy (AFM) analysis. Evalua tion of the kinetic parameters of the silver nucleation and the growth beha vior, as well as other characteristics of the silver electrocrystallization process onto carbon substrates, were based on cyclic voltammetry and chron oamperometric measurements. Cyclic voltammetry data also show that silver d eposition efficiency is proportional to the increase of electrode surface r oughness (from HOPG, via MPVC to FVC). The silver bulk deposition process o n all three carbon substrates was characterized as 3D nucleation and diffus ion-controlled growth. However, this process proceeds with different overpo tentials on different substrates: the lowest for HOPG and the highest for M PVC electrode surface. The major electrocrystallization parameters, such as nucleation rate, number of active sites, and number of fanned silver nucle i, 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 o pens new questions regarding the nature of the active sites for deposition on the electrode surface and their identification by microscopic techniques .