Janus MoSSe/WSSe Heterobilayers as Selective Photocatalysts for Water Splitting

Identifying materials that simultaneously straddle the water redox potentials and possess an intrinsic electric field is crucial for achieving high solar-to-hydrogen (STH) efficiency. Using state-of-the-art first-principles calculations, including a range-separated hybrid functional and spin-orbit coupling, we investigate MoXY/WXY (X, Y = S, Se) Janus bilayers for overall water splitting. We find that the Se–Se interfaced heterobilayer is intrinsically capable of driving water splitting, while its S–S counterpart can be tuned to meet the redox requirements through pH modulation. Both configurations show a high STH efficiency of 17.1%. Compared with homo-metal bilayers, hetero-metal bilayers benefit from the chemical potential difference between Mo and W, which generates a built-in electric field, which promotes spatial separation of photogenerated carriers, suppress recombination, and overall enhances hydrogen production. These results demonstrate the promise of Janus hetero-metal bilayers for efficient solar-driven water splitting.