Activating the Basal Plane of 2D Transition Metal Dichalcogenides via High-Entropy Alloying

Two-dimensional materials, such as transition metal dichalcogenides (TMDCs) in the 2H or 1T crystal phases, are promising (electro)catalyst candidates due to their high surface-to-volume ratio and composition of low-cost, abundant elements. While the edges of elemental TMDC nanoparticles, such as MoS₂, can show significant catalytic activity, the basal plane of the pristine materials is notoriously inert, which limits their normalized activity. Here, we show that high densities of catalytically active sites can be formed on the TMDC basal plane by alloying elements that prefer the 2H (1T) phase into a 1T (2H) structure. The global stability of the alloy, in particular, whether it crystallizes in the 2H or 1T phase, can be controlled by ensuring a majority of elements prefer the target phase. We further show that the mixing entropy plays a decisive role in stabilizing the alloy, implying that high-entropy alloying becomes essential. Our calculations point to a number of interesting nonprecious hydrogen evolution catalysts, including (CrTaVHfZr)S₂ and (CrNbVTiZr)S₂ in the 1T-phase and (MoNbTaVTi)S₂ in the 2H-phase. Our work opens new directions for designing catalytic sites via high-entropy alloy stabilization of locally unstable structures.