Uniform nitrogen and sulphur co-doped hollow carbon nanospheres as efficient metal-free electrocatalysts for oxygen reduction

Abstract

Developing highly efficient and low-cost electrocatalysts for the oxygen reduction reaction (ORR) to substitute precious Pt-based catalysts is highly important for the commercialization of advanced electrochemical energy conversion systems. Doped carbons have attracted wide attention and have become one of the hottest topics in new energy fields due to their high ORR performance and low cost. In this work, uniform nitrogen and sulphur co-doped hollow carbon nanospheres with an ultra-high surface area (1060 m² g⁻¹) were fabricated by using polyacrylonitrile and sulphur as the precursors. The catalyst exhibits outstanding ORR performance, excellent stability, methanol tolerance, as well as high selectivity toward the four-electron catalytic pathway. By analyzing the effects of sulphur addition, we found that the sulphur addition is crucial for the formation of uniform nanospherical morphologies, as well as highly porous structures and high surface areas. Besides, sulphur addition was also found to be able to modify the catalysts' atomic compositions effectively by increasing the total and pyridinic N contents while reducing oxidized N contents. Sulphur addition induced unique features in the catalysts' structures and compositions. We believe that this should be the main origins of our catalyst's outstanding ORR performance.