Tuning the phase stability and surface HER activity of 1T′-MoS2 by covalent chemical functionalization

Abstract

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.