As a simultaneous electrochemical measurement of oxygen reduction reaction (ORR) and surface oxidation/reduction on Pt/C, a shielding measurement using rotating ring disk electrode (RRDE) has been investigated. The ORR current was determined by the decrease of the ring current which was the diffusion limiting current of oxygen with collection efficiency of the RRDE. The difference between the disk current and the oxygen reduction reaction current was corresponded to cyclic voltammogram (CV) in inert atmosphere with correction of transient delay for the response of the ring electrode from the disk electrode. The delay of the ring electrode was 0.31 s for 6 mm in diameter of the disk electrode and 7 mm in the inner diameter of the ring at 900 rpm. To separate ORR current and CV clearly, significant level of the CV component in the disk current was needed. More than 40 µg cm−2 of Pt loading allowed the clear separation. At that time, apparent activity of Pt/C was less than one third of 10 µg cm−2 in Pt loading because of too thick the catalyst layer for the activity measurements. The mentioned above, the shielding measurement using RRDE could be applied for simultaneous separation of ORR and surface oxidation/reduction on Pt/C, and will be a strong tool to measure the relationship between the catalytic activity and the degree of the surface oxidation.
