M-N4 clusters embedded in graphene

The ORR on the M-N4 clusters embedded in graphene layer has also been studied to provide insight on the catalytic activity of heat-treated M-N4 macrocycles [179-183]. Limited by the local structure of extended graphene layer, only two configurations (Fig. 15) of the M-N4 clusters embedded in a graphene layer are quite possible. Active site A (Fig. 15a) is the most used model in literatures [179-183] while active site B (Fig. 15b) is also studied in Ref. [180]. 

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