The ORR electron transfer kinetics control via Co-N and graphitic N sites in cobalt single atom catalysts in alkaline and acidic media

Cost-effective 3d transition metal (TM) based single atom catalysts (SACs) for oxygen reduction reaction (ORR) are potential alternatives for Pt-based electrocatalysts in fuel cells and metal-air batteries. Understanding the effects of SACs’ properties and active site composition on the catalytic performance is significant to construct highly efficient catalysts. Here, we successfully promote the activity of cobalt single atoms decorated on N-doped carbon nanosheets via tuning the content of different nitrogen components, which outperforms most reported cobalt SACs. The activity and kinetics show positive correlation trends with the content of Co-Nx and graphitic N, serving as the main active sites. Furthermore, ORR kinetics in alkaline media can be positively affected by the conductivity of catalysts while no similar relation is observed in acidic media. The slight loss of Co-Nx sites engenders a mild change of performance in alkaline media, while the decrease of Co-Nx site activity due to chemical oxidation of carbon support and the loss of Co-Nx sites in acidic media exacerbate the degradation of performance. Our work provides an insight into the relation between ORR electron transfer kinetics and active sites in 3d TM based SACs.