Clarifying the Origin of Oxygen Reduction Activity in Heteroatom-Modified Defective Carbon

Metal-free oxygen reduction reaction (ORR) catalysts have been intensively studied during the past decade. For heteroatom-modified carbon materials, the influence of heteroatoms on the ORR remains unclear. Here, we use computational simulations to probe the role of heteroatoms in catalyzing the ORR; graphene with the pentagonal carbon (C5) defect is selected as a model catalyst in this study. Both theoretical and experimental results demonstrate that N and S co-doped graphenes without pentagons shows very poor ORR performance; however, in the presence of certain types of defects such as C5, the substitution of carbon atoms with N and S enhances the acidic ORR activity of the sample, implying the essential role of defects for the ORR. This work clarifies that heteroatoms themselves show limited contributions to the ORR, but they are powerful in tuning the electronic structures of defects for high ORR activity.