Sulphur and nitrogen co-doped graphene-based electrocatalysts for oxygen reduction reaction in alkaline medium

It is highly desirable to synthesise heteroatom-doped carbon-based materials in an environmentally friendly and simple way, which possess good electrocatalytic activity towards the oxygen reduction reaction (ORR). Therefore, in this study, we focused on comparing sulphur and nitrogen co-doped graphene-based materials prepared using simple synthesis procedures as ORR electrocatalysts. In particular, we considered two different sulphur and nitrogen precursors (thiosemicarbazide and trithiocyanuric acid) and either dry ball-milling or a wet method based on sonication followed by pyrolysis at 800 degrees C for S,N-co-doping of graphene. Electrochemical investigation of the S,N-co-doped catalysts using the rotating disc electrode (RDE) method showed superior ORR activity compared to the undoped graphene material, which is due to the synergetic effect of sulphur and nitrogen co-doping as well as to the defects present in the catalysts.