Ionically conducting 1-3 nm thick porous films of overoxidized polypyrrole (OPPY) were electrodeposited on nanostructured 7 mu m diameter carbon fiber microdisk electrodes. The microdisk electrodes were fabricated from two types of polyacrylonitrile (PAN) carbon fibers, PAN T650 and PAN HCB. The electrodes were nanostructured by electrochemical etching of the microdisk electrode surface. Ultrathin porous polypyrrole (PPY) films were electrodeposited by the electropolymerization of pyrrole (PY) to PPY by a short (10 ms) single potential pulse. During the electropolymerization, the polymer "precipitated" on the nanostructured surface producing ultrathin porous film. OPPY films were fabricated by constant potential overoxidation of PPY. In steady-state voltammetry of ferricyanide, the nanostructured electrodes behave as a random array of microscopic nodules and pores. At potential scan rates of 0.050 V s(-1) diffusion fields at the 300-600 nm nodules on the 7 mu m diameter microdisk electrode overlap. The surface area of the electroactive nanofeatures decreases after deposition of insulating OPPY. Kinetics of ferricyanide at bare and OPPY-coated nanostructured electrodes reflect the electrode surface area, as predicted by the model for charge transfer at a partially blocked surface. A model reflecting the 58-94% coverage of the nanostructured electrodes by OPPY was developed to address the high permeability of the porous OPPY-coated microdisk electrodes. (C) 2011 Elsevier Ltd. All rights reserved.