Contrasting Oxygen Reduction Reactions on Zero- and One-Dimensional Defects of MoS2 for Versatile Applications.

Oxygen reduction reaction (ORR) is a key microscopic process in many electrochemical applications of materials, where the requirements of their ORR performances may vary strikingly, for example, during the uses of MoS2 as an electrocatalyst and anticorrosion/lubricating coating in aqueous/humid environments, ORR should be activated and inhibited, respectively. To reveal a complete ORR profile of MoS2, using first-principles calculations, we examine the stabilities of various possible zero-dimensional point defects on the surface and one-dimensional edge defects and comprehensively explore the ORR activities on pristine MoS2 surface and those defects in acid/alkaline solutions. It is found that the ORRs on the pristine surface and surfaces with point defects always require large overpotentials (>1.0 V), indicating a defect-immune resistance of the planar MoS2 surface against the ORR. However, the ORR overpotentials on edge defects can reach as low as 0.66 V, corresponding to a relatively high activity close to that of the prototypical catalyst Pt (overpotential ∼0.45 V). Such contrasting ORR behaviors of point and edge defects are also understood in depth by analyzing the underlying thermodynamic and electronic-structure mechanisms. This work not only quantitatively explains the performances of MoS2 in both galvanic corrosion and electrochemical catalysis but also provides a useful structure-ORR map that can facilitate adapting the realistic MoS2 to versatile electrochemical applications.