Computational search for single-layer transition-metal dichalcogenide photocatalysts

Some of the members of the family of single-layer transition-metal dichalcogenides have recently received a lot of attention for their promising electronic properties, with potential applications in electronic devices. In this work, we focus on the stability of the dichalcogenides and determine their potential for photocatalytic water splitting. Using a first-principles design approach, we perform a systematic theoretical study of the dichalcogenides MX₂ (M = Nb, Mo, Ta, W, Ti, V, Zr, Hf, and Pt; X = S, Se, and Te). First, we use a van der Waals functional to accurately calculate their formation energies. The results reveal that most MX₂ have similar formation energies to those of single-layer MoS₂ and WS₂, implying the ease of mechanically exfoliating a single-layer MX₂ from their layered bulk counterparts. Next, we use the many-body G₀W₀ approximation to obtain the band structures, finding that about half of the MX₂ are semiconductors. We then calculate conduction and valence band edge positions by combining the bandgap center energies from the density-functional calculations and the G₀W₀ quasiparticle bandgaps. Comparing these band edge positions to the redox potentials of water, we identify that single-layer MoS₂, WS₂, PtS₂, and PtSe₂ are potential photocatalysts for water splitting. Furthermore, we find that PtSe₂ undergoes a semimetal-to- semiconductor transition when the dimension is reduced from three dimensional to two dimensional. Finally, large solvation enthalpies of these four candidate photocatalysts suggest their stability in aqueous solution.