Switch effect on controlled water splitting by biaxial strain regulating the promising two-dimensional Janus X 2 PAs (X = Si, Ge and Sn) photocatalyst.

Two-dimensional photocatalytic materials with unique properties have been well-reported in recent decades. However, strategies for controlling the photocatalytic process are still ongoing. Herein, Janus X 2 PAs (X = Si, Ge and Sn) monolayers have been explored by first-principles calculations to meet this challenge. All strain-free X 2 PAs monolayers exhibit excellent photocatalytic properties with high carrier mobility (2.39 × 10 2 -1.34 × 10 4 cm 2 V -1 s -1 ), suitable band edge positions straddling the standard redox potential of water and large visible light absorption coefficients (up to 10 5 cm -1 ). Most importantly, a reaction switch effect is proposed for the first time towards controlling the microscopic photocatalytic process of water splitting on X 2 PAs monolayers through macroscopic mechanical strain. This effect renders the Janus X 2 PAs photocatalytic switches among the states of only oxygen evolution reaction, only hydrogen evolution reaction and the full redox reaction for controlled water splitting. This work not only provides a new avenue for designing highly tunable photocatalysts but also offers new physical insights into controlling the photocatalytic water-splitting reaction.