Sulfur-doped carbon nanotubes as catalysts for the oxygen reduction reaction in alkaline medium

Based on the unique electronic properties and high surface area of carbon nanotubes as well as the similar electronegativity of sulfur and carbon, a novel electrocatalyst for the oxygen reduction reaction (ORR) was fabricated by directly annealing oxidized carbon nanotubes and p-benzenedithiol in nitrogen. The structural and chemical properties of the resulting sulfur-doped carbon nanotubes (pSCNTs) were investigated using transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. The catalytic activity of the pSCNTs towards ORR in alkaline medium was evaluated using rotating ring disk electrode voltammetry. The as-synthesized pSCNT-900 (annealed at 900 °C) exhibits excellent electrochemical performance towards ORR with an onset potential of -0.082 V (vs Ag/AgCl), a high kinetic current density of 34.6 mA cm−2 at -0.35 V), a dominant four-electron transfer mechanism (n = 3.71 at -0.35 V), as well as excellent methanol tolerance and durability. The results obtained are significant for the development of S-doped carbon-based catalysts for alkaline fuel cells.