Sulfur-doping achieves efficient oxygen reduction in pyrolyzed zeolitic imidazolate frameworks
We report the first synthesis of sulfurated porous carbon materials with well-defined morphologies and uniform N/S distributions via pyrolysis of zeolitic imidazolate frameworks loaded with sulfur-containing molecules. The optimized sulfurated catalyst demonstrates excellent electrocatalytic activity for the oxygen reduction reaction (ORR) in both acid and alkaline media. The sulfurization process under optimized conditions can lower the ORR over-potential by ca. 170 mV at 3 mA cm−2, giving a non-precious metal catalyst with an onset ORR potential of 0.90 V (vs. RHE, similarly hereinafter)/half-wave potential of 0.78 V in 0.1 M HClO4 and an onset ORR potential of 0.98 V/half-wave potential of 0.88 V in 0.1 M KOH. Furthermore, the S-doped porous carbon materials perform better in the long-term durability test than the non-S-doped samples and standard commercially available Pt/C. We also discuss different sulfuration methods for the ZIF system, morphologies of pyrolyzed samples, and catalytically active sites.