Oxygen electroreduction reaction (ORR) on pristine porous carbide derived carbons (CDCs) and on CDC supports modified with Pt-nanodusters has been studied in 0.5 M H2SO4 solution using cyclic voltammetry, rotating disk electrode and electrochemical impedance spectroscopy methods. The CDCs were prepared from Mo2C (noted as C(Mo2C)) at different fixed chlorination temperatures from 600 degrees C to 1000 degrees C. The CDCs have tuneable specific surface area, micro- and mesoporosity, good electrical conductivity and corrosion stability at positive electrode potentials. Pt-nanoclusters were deposited onto/into C(Mo2C) powders using sodium borohydride reduction method. The X-ray diffraction and high-resolution transmission electron microscopy were applied for the structural and chemical characterization, and the nitrogen sorption method was used for the porosity analysis of the electrode materials studied. The cathodic current densities depend strongly on the synthesis temperature of C(Mo2C), indicating that, in addition to the specific surface area and porosity, the crystallinity (density of defects in amorphous areas) has noticeable influence on the ORR rate. Impedance data demonstrated nearly capacitive behaviour in the low AC frequency region, explained by quick cathodic ORR followed by slow adsorption step of the intermediates and reaction products at/inside microporous-mesoporous C(Mo2C) and Pt-C(Mo2C) electrodes. (C) 2014 Elsevier Ltd. All rights reserved.