Passivation at a spherical cap microelectrode and comparison to a microdisk: Numerical simulation and experiment

As a model of passivation at a micro or nanoparticle, we have modelled a passivating reaction at a microelectrode of hemispherical geometry. The reaction is considered to lead to either the formation of a surface-bound species or diffusion of product into bulk solution. A dimensionless parameter, p, of value 0 to 1.0 can be used to describe the balance between the two processes. We have simulated the first two linear sweep voltammograms (LSV) under different values of p and have simulated the peak width of the first LSV under different values of scan rate and p. These simulations were used to relate the peak width to the value of p. The results were compared to the characteristics of passivation at a microdisk electrode. The equation was used to analyse the oxidation of dopamine at hemispherical Ga electrodes, fabricated by the deposition of liquid phase Ga onto Pt microdisks.