In this work we report on the influence of the catalytic layer architecture on the autocatalytic reaction of CO-bulk oxidation in liquid electrolyte by employing two types of nanomaterials: 2D arrays of Pt particles prepared on the surface of glassy carbon by colloidal lithography and 3D arrays of Pt nanoparticles supported on vertically aligned carbon nanofilaments. Oxidation of dissolved CO is studied experimentally using RDE approach and computationally using finite element method. For the first time, the influence of 3D architecture of the electrode on a complex bistable electrochemical system was investigated. The modelling results are in qualitative agreement with the experiment and explain the influence of nanostructure of the electrodes on such key characteristics of CO electrooxidation as the ignition potential, the width and the shape of the bistability region, and the value of the limiting current. Analysis of the experimental RDE curves suggests spontaneous formation of active and passive reaction zones along the fibre length which is supported by modelling.