Boron/Nitrogen Co-Doped Helically Unzipped Multiwalled Carbon Nanotubes as Efficient Electrocatalyst for Oxygen Reduction

Bamboo structured nitrogen doped multiwalled carbon nanotubes have been helically unzipped, and nitrogen doped graphene oxide nanoribbons (CN_x-GONRs) with a multifaceted microstructure have been obtained. CN_x-GONRs have then been codoped with nitrogen and boron by simultaneous thermal annealing in ammonia and boron oxide atmospheres, respectively. The effects of the codoping time and temperature on the concentration of the dopants and their functional groups have been extensively investigated. X-ray photoelectron spectroscopy results indicate that pyridinic and BC₃ are the main nitrogen and boron functional groups, respectively, in the codoped samples. The oxygen reduction reaction (ORR) properties of the samples have been measured in an alkaline electrolyte and compared with the state-of-the-art Pt/C (20%) electrocatalyst. The results show that the nitrogen/boron codoped graphene nanoribbons with helically unzipped structures (CN_x/CB_x-GNRs) can compete with the Pt/C (20%) electrocatalyst in all of the key ORR properties: onset potential, exchange current density, four electron pathway selectivity, kinetic current density, and stability. The development of such graphene nanoribbon-based electrocatalyst could be a harbinger of precious metal-free carbon-based nanomaterials for ORR applications.