Solution phase synthesis of halogenated graphene and the electrocatalytic activity for oxygen reduction reaction

Metal-free carbon electrocatalyts for the oxygen reduction reaction （ORR） are attractive for their high activity and economic advantages. However, the origin of the activity has never been clearly elucidated in a systematic manner. Halogen group elements are good candidates for elucidating the effect, although it has been a difficult task due to safety issues. In this report, we demonstrate the synthesis of CI-, Br- and I-doped reduced graphene oxide through two solution phase syntheses. We have evaluated the effectiveness of doping and performed electrochemical measurements of the ORR activity on these halogenated graphene materials. Our results suggest that the high electroneg- ativity of the dopant is not the key factor for high ORR activity; both Br- and I-doped graphene pro- moted ORR more efficiently than Cl-doped graphene. Furthermore, an unexpected sulfur-doping in acidic conditions suggests that a high level of sulfide can degrade the ORR activity of the graphene material.