The chemical inertness of the defect-free basal plane confers environmental stability to MoS₂ single layers, but it also limits their chemical versatility and catalytic activity. The stability of pristine MoS₂ basal plane against oxidation under ambient conditions is a widely accepted assumption however, here we report single-atom-level structural investigations that reveal that oxygen atoms spontaneously incorporate into the basal plane of MoS₂ single layers during ambient exposure. The use of scanning tunnelling microscopy reveals a slow oxygen-substitution reaction, during which individual sulfur atoms are replaced one by one by oxygen, giving rise to solid-solution-type 2D MoS_2−xO_x crystals. Oxygen substitution sites present all over the basal plane act as single-atom reaction centres, substantially increasing the catalytic activity of the entire MoS₂ basal plane for the electrochemical H₂ evolution reaction.

无缺陷基面的化学惰性赋予MoS ₂单层环境稳定性，但也限制了它们的化学多功能性和催化活性。原始MoS ₂基面在环境条件下抗氧化的稳定性是一个广为接受的假设，但是，在此我们报道了单原子级的结构研究，该研究表明氧原子在环境暴露过程中自发地结合到MoS ₂单层基面中。扫描隧道显微镜的使用显示了缓慢的氧取代反应，在此期间，单个硫原子被氧一个一个地取代，从而产生了固溶体型2D MoS ₂ - _x O _x晶体。存在于整个基面上的氧取代位点充当单原子反应中心，从而大大提高了整个MoS ₂基面对电化学H ₂析出反应的催化活性。