Tuning the phase stability and surface HER activity of 1T′-MoSby covalent chemical functionalization

The metallic phase of 1T′-MoShas triggered versatile investigations owing to its high activity towards the hydrogen evolution reaction (HER) both on the edges and basal plane. However, the structural instability of the metastable 1T′-MoSrestricts its practical applications. Covalent functionalization has been widely used to modify the intrinsic properties of low-dimensional nanomaterials. Here, we explore the potential of covalent chemical functionalization in modulating the stability and catalytic activity of the 1T′-MoSmonolayer by first-principles calculations. We probed the benchmark H and a series of carbon-terminated functional groups, and found that surface functionalization via formation of covalent S-H or S-C bonds can effectively stabilize 1T′-MoSagainst its conversion back to the 2H phase. The critical coverage needed for 1T′ stabilization is 33.3% for H and 25.0% for the C-terminated groups. Different from the semi-metallic character of pristine 1T′-MoS, the electronic structure of chemically functionalized 1T′-MoSis adsorbate-dependent, which can be a semiconductor or a metal. Moreover, compared to the pristine 1T′-MoS, we identified that the-CHCHOH and-CHCOOH functionalized 1T′-MoScan well balance the electrocatalytic HER activity and stability, and the activity at some of the surface S sites even outperforms that of the pristine 1T′-MoS. This study provides a useful chemical route to control the phase stability, electronic properties and electrocatalytic performances of thermodynamically unstable 1T′-MoSand other transition metal dichalcogenides.