Theoretical aspects of light activated semiconductor microelectrodes: A generalized analysis

Theoretical aspects of light activated semiconductor (SC) microdisk electrodes in redox electrolytes have been examined as a function of the dimensionless photon flux σ and dimensionless bias potential ω_bias. Dimensionless steady-state profiles for solid-state and solution phase species were obtained by solving self-consistently the transport equations and the electrostatic potential within the SC subject to the appropriate boundary conditions using COMSOL. Analyses of the results obtained revealed that for fixed σ and small ω_bias, the local dimensionless flux at the interface normal to the SC surface, J _Z(R,0), where R is the dimensionless radius normal to the axis of symmetry, is dominated by the oxidation process in the illuminated region (R≤1) and by the reduction process in the dark area near the edge of the illuminated region. For large ω_bias, however, the oxidation process dominates JZ (R,0) everywhere along the interface. Agreeing with the phenomenon described in our earlier publication, the holes escape beyond R=1, yielding, for very large values of ω_bias and σ, a total current flowing through the dark area that can exceed that collected within the illuminated disk.