Increase of structural defects by N doping in MoS2 cross-linked with N-doped CNTs/carbon for enhancing charge transfer in oxygen reduction

Abstract

To improve the sluggish kinetics of oxygen reduction reaction (ORR) is critically important for the development of fuel cells. It is generally recognized that catalysts with multi-transfer channels and varied active sites can energetically facilitate the ORR-relevant species transfer to improve the oxygen reduction rate. In this study, N-doped carbon nanotubes-crossed MoS2/carbon (N-MoS2/CNTs/C) catalysts are synthesized at temperatures of 600–900 °C using an in-situ reduction self-assembly method. In both acid (0.5 M H2SO4) and alkaline (0.1 M KOH) media, N-MoS2/CNTs/C (800 °C) catalyst exhibits a promising ORR activity and favors a four-electron reduction pathway. The highly-maintained tubular CNTs in N-MoS2/CNTs/C (800 °C) can supply the multidimensional pathways for transferring the ORR-relevant species. N atoms doping can not only increase the structural defects of MoS2 lattice (Mo–Nx) to expose more Mo–Sx sites, but also induce various N functional groups into the carbon matrix (CNTs and porous carbon), which are favorable to improve the activation, adsorption and reduction of oxygen. Therefore, the distinct structures endow the N-MoS2/CNTs/C catalysts with high activity towards ORR. Furthermore, the N-MoS2/CNTs/C (800 °C) also exhibits a promising ORR activity in neutral medium (microbial fuel cells (MFCs)). MFCs with the N-MoS2/CNTs/C (800 °C) cathode exhibits the maximum power density of 987.4 mW m−2, which is much higher than that of commercial Pt/C (601.96 mW m−2). These results indicate that N-MoS2/CNTs/C catalysts can be considered as a promising alternative to Pt/C for ORR.