Janus effect of O₂ plasma modification on the electrocatalytic hydrogen evolution reaction of MoS₂

Oxygen incorporation is a promising and effective way for simultaneously engineering the edge and planar sites of MoS₂ to fabricate high-performance HER electrocatalysts. However, the insulating MoO₃ species are inevitably generated during the oxygen incorporation process. Here, controlled plasma exposure time has been designed to explore the influence of MoO₃ species on the HER performance for the O₂ plasma modified MoS₂ catalysts. We find that the MoO₃ species in MoS₂ are not conductive to the HER electrocatalysis. More importantly, the Raman spectrum, X-ray photoelectron spectroscopy, energy-disperse X-ray spectrum and transmission electron microscope analyses demonstrate that these co-generated MoO₃ species are reduced and resolved from the MoS₂ lattice during the electrocatalytic hydrogen evolution, leading to a holey structure in the MoS₂ nanosheets and thus a significant improvement of its hydrogen evolution stability. This work not only helps to understand the electrocatalytic influence of the co-generated MoO₃ species in MoS₂, but also presents a methodological improvement in designing defect-rich, oxygen incorporated and holey MoS₂ nanosheets for highly efficient hydrogen evolution.