Oxygen Reduction Reaction Promoted by the Strong Coupling of MoS2 and SnS

Graphene-like molybdenum disulfide (MoS2) with unique catalytic features and chemical/electrochemical stability holds great potential as an oxygen reduction reaction (ORR) catalyst, but the overall weak oxygen adsorption and low electron conductivity limit its catalytic activity. Herein, MoS2 strongly coupled with an oxophilic SnS heterostructure embedded in nitrogen-doped porous carbon sheets (MoS2-SnS/NPC) was developed. The coupled SnS can not only tune the electronic structure but also promote the oxygen molecule adsorption and activation. Moreover, NPC can enhance the electron transfer as well as the structural stability of the MoS2-SnS heterostructure without agglomeration. As expected, MoS2-SnS/NPC exhibited enhanced catalytic activity that is superior to those of MoS2/NPC and SnS/NPC along with good catalytic stability for ORR. As a cathode catalyst, a homemade zinc–air battery driven by MoS2-SnS/NPC showed considerable discharging performance superior to the one driven by a commercial Pt/C catalyst in terms of open-circuit voltage, peak power density, and specific capacity. Furthermore, a MoS2-SnS/NPC-based zinc–air battery displayed a stable charging and discharging voltage gap for 48 h without an expanding trend, suggesting a robust cycling performance and heralding promising application prospects. The rotating ring-disk electrode and in situ electrochemical Raman tests revealed that the ORR underwent a combined 2-electron and 4-electron associative mechanism on MoS2-SnS/NPC, and the improved catalytic activity came from the synergistic effect of MoS2, SnS, S vacancy, and porous carbon sheets. This study provided a heterojunction strategy by coupling oxophilic SnS for boosting ORR electrocatalysis, which can be extended to other cheap transition-metal catalysts for efficient energy conversion.