Efficient Synthesis of Nitrogen- and Sulfur-co-Doped Ketjenblack with a Single-Source Precursor for Enhancing Oxygen Reduction Reaction Activity.

Promoting the oxygen reduction reaction (ORR) catalytic activities of cost-effective catalysts is of great significance for the development of various energy conversion and storage systems. Herein, we describe the preparation of a highly active N- and S-co-doped ketjenblack (Kb) by facile pyrolysis of a mixture of thiourea and Kb in the presence of FeCl3 ⋅6 H2 O followed by an acid-leaching process. This novel synthetic approach was rationally designed with the consideration that thiourea could easily introduce both N and S heteroatoms into the carbon matrix by a heat-treatment method by releasing plentiful reactive N- and S-containing gases, which could simultaneously optimize the porous structure of the resultant catalyst. Physical characterization revealed that N and S were homogeneously incorporated into the nanostructure of Kb and formed a hierarchical porous structure with a high specific surface area. The N/S-Kb catalyst showed impressive ORR activity, with an onset potential of 0.08 V at 0.1 mA cm-2 , which is 20 mV more positive than that of commercial 20 wt. % Pt/C catalyst. This was coupled with long-term durability and superior methanol tolerance in alkaline media. The improved ORR performance can be mainly ascribed to synergistic contributions of highly efficient active sites arising from high contents of thiophene S and pyridinic N along with the high specific surface area and the favorable mass-transport properties arising from the hierarchical porous structure. The remarkable ORR performance and facile preparation method make the N/S-Kb catalyst a promising substitute for Pt in electrochemical energy devices.