Sulfur-doped carbon spheres as efficient metal-free electrocatalysts for oxygen reduction reaction

Sulfur-doped carbon spheres have been synthesized via an in-situ doping approach and solvothermal method using sucrose as carbon source and benzyl disulfide as sulfur source. The as-prepared S-doped carbon spheres have microporous structure with a high specific surface area of > 503.0 m2 g−1. The electrocatalytic activity of S-doped carbon spheres for oxygen reduction reaction (ORR) in alkaline media has been studied through a rotating ring-disk electrode (RRDE) technique. Compared with non-doped carbon spheres, all S-doped carbon spheres show enhanced ORR activity. The effect of S-doping content on the catalytic activity has been studied, the sample containing 4.0 at. % of S exhibits high electrocatalytic activity and superior stability for the ORR. This highlights the critical role of optimized S content on the ORR activity enhancement. The improved electrocatalytic activity and stability of S-doped carbon sphere are primarily ascribed to appropriate S-doping into the carbon lattice in combination with the high specific surface area of carbon spheres.