Janus PtXO (X = S, Se) monolayers: the visible light driven water splitting photocatalysts with high carrier mobilities.

Triggered by the recent experimental synthesis of the Janus PtSSe monolayer, we use the first-principles calculations to predict two new Janus photocatalysts PtXO (X = S, Se), based on the systematic investigations of the structural stabilities, electronic structures, band alignments, catalytic activity and optical absorption. The two Janus structures are found to be mechanically, dynamically and thermodynamically stable, and have suitable band edge positions for the overall water splitting. Owing to the high electron mobility (up to 2164.95 cm2 V−1 s−1) and large disparity between the electron and hole mobilities, together with the indirect band gaps and the intrinsic dipole induced built-in electric fields, the photogenerated electrons/holes can be efficiently separated in PtXO. Moreover, the S/Se vacancy can effectively lower the free energy difference of the HER, making the catalytic reactions occur spontaneously under the potentials of photoexcited electrons and holes. Large optical absorption coefficients (105 cm−1) are also confirmed in the visible light range, and the biaxial tensile strain can further enhance the optical absorption while maintaining the capability of the overall water splitting. Our results not only propose two new Janus materials by demonstrating the possibility of experimental realization, but also indicate that PtXO are peculiar candidates for photocatalytic water splitting.