The influence of the structural properties of carbon on the oxygen reduction reaction of nitrogen modified carbon based catalysts

Nitrogen modified carbon based catalysts for the oxygen reduction reaction (ORR) were synthesized using three different types of carbon, carbon black (CB), carbon nanotube (CNT) and platelet carbon nanofiber (P-CNF) with nitrogen containing organic precursors. The relationship between the ORR activity and the carbon nanostructure was explored using various electrochemical and physical characterization methods. It was found that the ORR activity was affected by the type and content of the nitrogen functional group instead of the carbon surface area. The formation of nitrogen functional group, in turn, strongly depends on the carbon nanostructure. Unlike the basal plane, the edge plane exposure provides the appropriate geometry for the nitrogen incorporation into carbon structure, resulting in high nitrogen content and high pyridinic-N and graphitic-N content, providing an active site for ORR. Therefore, the P-CNF based catalyst with the highest edge plane exposure has the highest ORR activity despite having the smallest surface area.