Understanding the Oxygen Reduction Reaction Activity of Quasi-1D and 2D N-Doped Heat-Treated Graphene Oxide Catalysts with Inherent Metal Impurities

Carbon-based nanomaterials (fullerenes, carbon nanotubes, graphene derivatives, etc.) are promising cost-effective catalyst alternatives to noble metal catalysts for the oxygen reduction reaction (ORR). Herein, we report on the synthesis and characterization of graphene-based derivatives with various aspect ratios. All the synthesized materials were critically probed for activity and stability for ORR in acidic and alkaline electrolytes. Namely, a comparison study on the influence of aspect ratio and N-doping on ORR electroactivity in acidic and alkaline electrolytes of quasi-1D N-doped heat-treated graphene oxide nanoribbons (N-htGONr) with 2D N-doped heat-treated graphene oxides (N-htGO) was done. Moreover, we also investigated the influence of metallic impurities on the ORR activity in acidic and alkaline media. We have shown that a higher aspect ratio plays an important role in improving ORR activity. Furthermore, when comparing N-doped derivatives with non-doped derivatives, the ORR activity in 0.1 M HClO4 is increased by N-doping; however, in 0.1 M KOH, the N-doping effect is overshadowed by inherent transition metal impurities, i.e., iron. In this respect, we have established a linear correlation between onset potential for ORR, iron concentration, and BET specific surface area of graphene-based derivatives. The present study will aid in the critical assessment and development of non-metallic catalysts for the electrochemical energy conversion devices.