Nitrogen containing carbon spheres as an efficient electrocatalyst for oxygen reduction: microelectrochemical investigation and visualization

Abstract

The oxygen reduction reaction (ORR) in low temperature fuel cells limits the obtainable output triggering the necessity of screening the employable catalysts precisely. A nitrogen-containing carbon sphere (NCS) catalyst was synthesized using a soft template and was studied for the oxygen reduction reaction. The NCS catalyst was shown to have superior activity with an onset potential of 0.985 V (vs. RHE) and a diffusion-limited current density of 6.16 mA cm 2 . The kinetic insight from the rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) revealed an overall 4e reduction by a (2 + 2) electron pathway with a rate constant of 4.6 10 4 cm s 1 at the onset potential. A fast screening of the localized electrochemical activity using sample generation-tip collection (SG-TC) in combination with a chronoamperometric multiple pulse technique was applied in the present study to trace the formation, evolution and conversion of intermediate species using a Pt ultramicroelectrode. The local catalytic activity of the NCS catalyst was successfully visualized by scanning electrochemical microscopy (SECM) in highly alkaline medium.