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.