The adsorption and electro-oxidation of ethylene in acid electrolyte were studied on differently prepared platinum electrodes. A clear dependence of the apparent specific catalytic activity for ethylene electro-oxidation on platinum electrode structure was observed. Platinized platinum electrodes exhibit a low apparent specific catalytic activity which decreases on increasing the roughness factor due to additional overpotential contributions within the pores. The specific adsorptive characteristics and catalytic activity of non-porous platinum electrodes prepared by electroreduction of thick platinum oxide layers are independent of roughness factor and similar to those of smooth platinum electrodes.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas