Nitrogen and sulfur co-doped porous carbon sheets for energy storage and pH-universal oxygen reduction reaction

Developing efficient electrocatalysts for energy storage and oxygen reduction reaction (ORR) is of great significance for the utilization of renewable energy. In particular, designing catalysts with both promising activity and long stability for ORR in pH-universal electrolytes still remain as a tremendous challenge. To tackle such a problem, metal-free nitrogen and sulfur co-doped porous carbon sheet (NSPCS) was rationally designed in this work in order to integrate the two reported routes of enhancing the electrocatalytic activity of graphene. The as-prepared NSPCS has an onset potential of 0.89 V vs. RHE, and half-wave potential E-1/2 approximate to 0.75 V during ORR in acidic solution, making it as the most active ORR catalyst. Moreover, the resulting NSPCS also shows a 0.03 V positive shift of half-wave potential than commercial Pt/C for ORR and excellent charge capacitive performance in alkaline media. Electron microscopy revealed high degree of defects on NSPCS surface. This, coupled with synergistic doping effects of nitrogen and sulfur, optimized the active sites and charge transfer, rationalized the outstanding performance in both oxygen reduction reactions and supercapacitors.