The mechanism of the oxygen reduction reaction (ORR) in a naturally aerated stagnant 0.5 M H2SO4 Was studied using electrochemical methods. The cathodic polarization curve showed three different regions; electrochernical impedance spectroscopy (EIS) measurement was used accordingly. The EIS data were analyzed, and the mechanism for the ORR was proposed consequently. The three regions include a limiting current density region with the main transfer of 4e(-) controlled by diffusion (-0.50V < E < -0.40V), a combined kinetic-diffusion region (-0.40V

Keywords:Oxygen reduction;Hump phenomenon;Chemical redox;Copper;Electrochemical impedance spectroscopy