Mo-Terminated Edge Reconstructions in Nanoporous Molybdenum Disulfide Film

The catalytic and magnetic properties of molybdenum disulfide (MoS₂) are significantly enhanced by the presence of edge sites. One way to obtain a high density of edge sites in a two-dimensional (2D) film is by introducing porosity. However, the large-scale bottom-up synthesis of a porous 2D MoS₂ film remains challenging and the correlation of growth conditions to the atomic structures of the edges is not well understood. Here, using molecular beam epitaxy, we prepare wafer-scale nanoporous MoS₂ films under conditions of high Mo flux and study their catalytic and magnetic properties. Atomic-resolution electron microscopy imaging of the pores reveals two new types of reconstructed Mo-terminated edges, namely, a distorted 1T (DT) edge and the Mo-Klein edge. Nanoporous MoS₂ films are magnetic up to 400 K, which is attributed to the presence of Mo-terminated edges with unpaired electrons, as confirmed by density functional theory calculation. The small hydrogen adsorption free energy at these Mo-terminated edges leads to excellent activity for the hydrogen evolution reaction.