Carbon nanotube supported zinc, cobalt, nitrogen, sulfur-doped porous carbon as electrocatalyst for enhanced oxygen reduction reaction

Abstract

Carbon nanotube (CNT) supported zinc, cobalt, nitrogen, sulfur-doped porous carbon (CNT@ZnCo/NSC) catalysts are prepared by in situ growth of sulfur-containing bimetal zeolitic imidazolate framework (S–ZnCo-ZIF) polyhedrons on CNT with subsequent heat treatment. The microstructure, morphology, particle size distribution, specific surface area, and pore-size distribution of the catalysts are characterized by multiple techniques. CNT@ZnCo/NSC exhibits excellent catalytic activity for oxygen reduction reaction (ORR) with onset potential of 0.98 V and half-wave potential of 0.83 V, respectively, which are close to those of Pt/C. The addition of CNT inhibits the agglomeration and improves the conductivity of the catalysts, while S doping enhances the electrochemical surface area and introduces active sites. The special structure makes CNT@ZnCo/NSC possess proper specific surface area (390.8 m2 g−1) and large average pore size (5.26 nm). CNT@ZnCo/NSC contains more graphite-N (21%) and pyridine-N (55.9%) than CNT@ZnCo/NC (20%, 46.5%) and ZnCo/NC (8.2%, 45.8%). CNT@ZnCo/NSC catalyst has better methanol tolerance and long-term stability than commercial Pt/C.