Core-shell S-doped g-C3N4@P123 derived N and S co-doped carbon as metal-free electrocatalysts highly efficient for oxygen reduction reaction

The advantage of g-C3N4 as nitrogen-rich precursor for synthesizing nitrogen-doped carbon-based oxygen reduction reaction (ORR) catalyst has not been brought into full play. Herein, a simple approach with S-doped g-C3N4 (S-g-C3N4) and P123 as precursor for synthesizing nitrogen and sulfur co-doped carbon (N-S-C) catalysts highly efficient for ORR was developed. S-g-C3N4 synthesized via pyrolysis of a mixture of urea and thiourea was used as nitrogen and sulfur source, and P123 serving as carbon source was used to envelop S-g-C3N4 to form core–shell S-g-C3N4@P123 sample, whose pyrolysis yielded N-S-C catalyst. Characterization shows that the N-S-C catalyst synthesized at 900 °C with a S-g-C3N4/P123 mass ratio of 2:1 (N-S-C-2) exhibits the largest nitrogen and sulfur content and the highest half-wave potential of 0.863 V vs. RHE in alkaline media, which can be ascribed to the selection of the mixture of urea and thiourea for S-g-C3N4 synthesis, and the suitable S-g-C3N4/P123 mass ratio and pyrolysis temperature. N-S-C-2 also shows good ORR catalytic stability, excellent methanol tolerance, and high performance as the cathodic catalyst of Zn-air battery. This study gives full play to the advantage of g-C3N4 and provides a novel route for synthesizing N-S-C catalysts highly efficient for ORR.