Sulfur and nitrogen co-doped carbon nanotubes for enhancing electrochemical oxygen reduction activity in acidic and alkaline media

Carbon materials have received an increasing amount of attention due to their low cost, long-term stability, and high electrocatalytic activity in catalyzing the cathodic oxygen reduction reaction (ORR). However, most of the carbon catalysts have exhibited their excellent activity only in alkaline media, which greatly hinders their practical application in polymer electrolyte membrane fuel cells (PEMFCs). In order to break the restriction of alkaline conditions, sulfur and nitrogen doped carbon nanotubes (SN-CNTs) were designed and successfully prepared via annealing of a mixture composed of nitrogen doped carbon nanotubes (N-CNTs) and sulfur. The result showed the as-prepared SN-CNTs have an enhanced ORR activity in both acidic and alkaline media compared with N doped CNTs (N-CNTs). This report also provides a new approach to explore low-cost electrocatalysts for practical fuel cell applications.