Comparison between effective electrode/electrolyte interface potential and applied potential for gold electrodes

A nonlinear solution of the Poisson-Boltzmann equation between two interacting surfaces was used to model the interaction force between a gold electrode and a standard silicon-nitride cantilever tip employed in atomic force microscopy (AFM). AFM measurements were used to calculate the effective gold electrode/electrolyte solution interface potential via minimization of the error between predicted interaction force values and those measured via AFM. Analysis of the data reveals that an effective electrode/electrolyte potential, rather than the applied potential to the electrode, is responsible for the interaction forces observed in this work. Further examination of the gold electrode/electrolyte interface via cyclic voltammetry reveals that, despite the fact that the gold electrode is considered inert, some degree of association of ions present in the solution with the gold electrode occurs. Accumulation of different ions in the solution at the electrode/electrolyte interface determines the magnitude of the effective potentials at different conditions of pH and ionic strength. At extreme conditions of pH, electrosorption of ionic species could be detected.