Electrochemical behaviour of sandwich-type composite electrodes of polypyrrole (PPy) and CoFe2O4 nanoparticles (Ox) were investigated in an aqueous solution of 0.5 M K2SO4 and 5mM KOH at 25 degreesC using electrochemical impedance (EI), cyclic voltammetry (CV) and Tafel polarization techniques. EI and CV studies indicated that the incorporation of oxide nanoparticles influenced the charge transfer and transport behaviours of the polymer matrix greatly. The bulk electrical resistances of pure polymer (4.5 +/- 1.7 Omega) as well as composite (2.7 +/- 0.8 Omega) electrodes were practically constant in the potential region, +0.1 to -0.7 V. The latter electrode showed a good electrocatalytic activity towards the oxygen reduction reaction (ORR). (C) 2004 Published by Elsevier Ltd.