We recently introduced new methodology for detecting charged reactive intermediates of heterogeneous processes and used it to investigate the oxygen reduction reaction at polycrystalline Pt.  A nanometer-sized pipette filled with organic solvent immiscible with the external aqueous solution was used as a tip in the scanning electrochemical microscope (SECM) to detect and identify a short-lived superoxide intermediate and determine the rate of its generation at the catalytic Pt substrate.  The interpretation of that experimental data was based on a simplified model that left a number of open questions about superoxide desorption and its lifetime in neutral aqueous solution.  Here we report the results of finite element simulations based on a more exact model and aimed at the detailed mechanistic analysis of this system.