Nonequilibrium fluctuation theory in electrochemical nucleation. II. Experimental determination of critical fluctuation in silver nucleation onto platinum electrode

Abstract

Following part I, in this paper, the experiments for silver nucleation onto platinum electrode in AgNO3+NaNO3 solution were carried out to compare the theoretical equations with experimental data. The theoretical examination predicted that after double layer charging current a minimum current emerges, accompanied with rapid monolayer nucleus formation. Since the monolayer nuclei prepare the substrates for the following extensive nucleation, the stage when the nuclei are formed is of much importance. From the experiments for double layer charging current, it was decided that the nucleus formation is activated at the final stage of the charging. This result reinforces the theoretical prediction that the monolayer nuclei are formed by the minimum current. Extrapolation of the minimum current to the critical state gave the critical autocorrelation distance and the average critical concentration fluctuation on the completely active surface. The autocorrelation distance was determined as ãcr=7.82×10−4 m at 300 K, which is quite large in comparison with the scale of the fluctuation and in good agreement with the value obtained in nickel pitting dissolution. On the other hand, as discussed in the previous paper, since there is no intense specific adsorption of ions onto the electrode surface, the electrostatic interaction between the ions accelerates the simultaneous adsorption of Ag+ ion and NO3− ion. Therefore, it was concluded that the concentration of the supporting electrolyte NaNO3 also fluctuates with the Ag+ ionic concentration.