Exploration of the catalytically active site structures of animal biomass-modified on cheap carbon nanospheres for oxygen reduction reaction with high activity, stability and methanol-tolerant performance in alkaline medium

Nitrogen-doped carbon materials are known to exhibit good electrocatalytic activity for the oxygen reduction reaction (ORR). However, the structure of the active site for the ORR remains unknown. In this work, a series of nitrogen-doped carbon nanospheres (N-CNSs) were successfully prepared by using porcine blood protein as specific nitrogen source at different pyrolysis temperatures. The results show that the catalyst with a higher percentage of the planar N species (83.5% in total nitrogen content), possesses outstanding ORR electrocatalytic activity close to the commercial 40% Pt/C catalyst in alkaline media, and significantly superior stability and immunity for methanol crossover than that of 40% Pt/C. Metal Fe particles in the precursor can facilitate the partial transformation of oxidized N to planar N and the joint incorporation of planar pyridinic and pyrrolic N groups into the carbon matrix during high-temperature pyrolysis, which further produces more defective and exposed edges in the carbon structure. It is here proposed that both planar pyridinic and pyrrolic nitrogen atoms may be the N functionalities that are most responsible for the ORR electrocatalytic activity and can function as ORR active sites for as-prepared catalysts.