Carbon Nanotubes/Heteroatom-Doped Carbon Core-Sheath Nanostructures As Highly Active Bifunctional Oxygen Reduction and Oxygen Evolution Electrocatalysts

Abstract

An ionic liquid (IL)-driven, facile, scalable route to new carbon nanostructures comprising pure carbon nanotube cores and heteroatom-doped carbon sheath layers (CNT/HDC) has been developed. The design of the CNT/HDC nanocomposites allows for combining electrical conductivity derived from the CNTs with the catalytic activity of the heteroatom-containing HDC sheath layers. The CNT/HDC nanostructures showed excellent electrocatalytic activity for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in an alkaline medium. The ORR activity of CNT/HDC nanostructures is one of the best performances among the heteroatom-doped nanocarbon catalysts in terms of half-wave potential and kinetic current density. The kinetic parameters of the CNT/HDC nanostructures, including 4-electron transfer selectivity and exchange current density, compared favorably with those of a Pt/C catalyst. The CNT/HDC nanostructures also exhibited superior long-term durability and poison-tolerance relative to Pt/C. Bifunctional oxygen electrocatalytic activity of CNT/HDC was comparable to that of Ir/C and better than that of Pt/C. In addition, the CNT/HDC nanostructures showed high current and power densities when employed as a cathode catalyst in alkaline fuel cell, which sheds light on their practical applicability.