Tuning the phase stability and surface HER activity of 1T′-MoS2 by covalent chemical functionalization†
The metallic phase of 1T′-MoS2 has 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′-MoS2 restricts 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′-MoS2 monolayer 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′-MoS2 against 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′-MoS2, the electronic structure of chemically functionalized 1T′-MoS2 is adsorbate-dependent, which can be a semiconductor or a metal. Moreover, compared to the pristine 1T′-MoS2, we identified that the –CH2CH2OH and –CH2COOH functionalized 1T′-MoS2 can 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′-MoS2. This study provides a useful chemical route to control the phase stability, electronic properties and electrocatalytic performances of thermodynamically unstable 1T′-MoS2 and other transition metal dichalcogenides.