Chemically stabilized DT-MoS₂ alloys for enhanced hydrogen-evolution-reaction

The hydrogen evolution reaction (HER) refers to the splitting of H₂ molecules. Pt works best, but high cost limits its utility in large-scale applications. MoS₂, owing to the low cost of its components and good stability has emerged as an alternative to Pt. However, the basal plane of the 2H phase of MoS₂ is catalytically inert as only edges and voids catalyze the H production process. In this work, we use density functional theory calculations and electron microscopy to demonstrate that DT-phase MoS₂ can be stabilized by alloying with 50% Re, which leads to significant improvement in HER performance. We find that DT-phase Re_0.55Mo_0.45S₂ shows low overpotential and, therefore, exhibits enhanced catalytic activity. For DT-phase alloys with x>0.75, a high overpotential and low HER activity is observed. In order to evaluate HER activity and the mechanism responsible for low overpotential in Re-doped MoS₂ monolayers, we calculated the Gibbs free energy (ΔG_H) for hydrogen adsorption. We find that ΔG_H for Re_0.55Mo_0.45S₂ strongly depends on the local environment and the most active sites are S atoms surrounded by three Mo atoms with ΔGH being close to zero. Thus, the presence of Re impurities only serve to stabilize the DT phase, but are not directly involved with the catalysis process.