Controllable etching of MoS2 basal planes for enhanced hydrogen evolution through the formation of active edge sites

The catalytic activity of molybdenum disulfide (MoS2) is associated with active sites located along the edges, whereas the MoS2 basal plane is regarded to be inert. However, it is a great challenge to develop a rational way for producing active edges efficiently. Herein, we report a novel, cost-effective top-down process in which we can create a high density of active edge sites on MoS2 basal plane by selective steam etching. The results show that the etched structure is strongly sensitive to the temperature, which creates 1D nano-channels, 2D in-plane triangular pits and 3D vertical hexagonal cavities on the MoS2 basal planes by elevating the temperature. The edge configuration is revealed to exhibit a distinct crystallographic orientation. Furthermore, we evaluate the corresponding enhanced electrocatalytic activity for the hydrogen evolution reaction (HER) by measurements of the single etched MoS2 samples in an electrochemical microcell, where the Tafel slope decrease by 49%, confirming the increased the density of active sites. In addition, the method is not limited to 2D materials in a flat geometry alone, but is also demonstrated on OD MoS2 particles by in-situ transmission electron microscopy. The steam etching reported here offers an alternative avenue to engineer the surface structures of MoS2 facilitating the electrocatalytic applications of MoS2 for hydrogen production.