Preparation of Chemically Structure-Controlled BN-Doped Carbons for the Molecular Understanding of Their Surface Active Sites for Oxygen Reduction Reaction

BN-doped carbons have been reported to exhibit higher oxygen reduction reaction (ORR) activities than single-atom-doped carbons. However, the structures of these BN-doped carbons as well as the mechanism underlying their catalytically active sites had not been elucidated. In the BN-doped carbons reported so far, B and N exist in a disordered manner within the carbon structure. Therefore, it is extremely difficult to determine the chemical structures of the active sites of these carbons. In this study, we prepared chemically structure-controlled BN-doped carbons by selectively introducing B–N–C moieties using a method based on organic molecular reactions. B and N in the prepared BN-doped carbons were mainly in the form of B–N–C moieties. The ORR catalyzed by these BN-doped carbons showed a higher number of transferred electrons, which was attributable to the electrochemical H2O2 reduction capability of the BN-doped carbon being enhanced by the BN doping. Furthermore, we prepared and evaluated BN-doped carbons with controlled amounts of B–N–C moieties and confirmed that there exists a strong correlation between the amount of B–N–C moieties and the ORR activity. These findings indicate that the B–N–C moieties in BN-doped carbons serve as the active sites for the ORR.