Oxygen Reduction on Graphene–Carbon Nanotube\nComposites Doped Sequentially with Nitrogen and Sulfur

Abstract

The development of unique, reliable,\nand scalable synthesis strategies\nfor producing heteroatom-doped nanostructured carbon materials with\nimproved activity toward the electrochemical oxygen reduction reaction\n(ORR) occurring in metal–air batteries and fuel cells presents\nan intriguing technological challenge in the field of catalysis. Herein,\nwe prepare unique graphene–carbon nanotube composites (GC)\ndoped sequentially with both nitrogen and sulfur (GC-NLS) and subject\nthem to extensive physicochemical characterization and electrochemical\nevaluation toward the ORR in an alkaline electrolyte. GC-NLS provides\nORR onset potential increases of 50 and 70 mV in comparison to those\nof dual-doped individual graphene and carbon nanotubes, respectively.\nThis highlights the significant synergistic effects that arise because\nof the nanocomposite arrangement, consisting of highly graphitized\ncarbon nanotubes assembled on the surface of graphene sheets. The\naddition of sulfur as a co-dopant is also highly beneficial, providing\nan 80 mV increase in the ORR onset potential in comparison to that\nof GC nanocomposites doped with only nitrogen. Excellent electrochemical\nstability of GC-NLS is also observed through 5000 electrode potential\ncycles, indicating the promising potential of this new class of dual-doped\nGC nanocomposites as ORR catalysts.