Two-Dimensional Lateral Heterostructures of Triphosphides: AlP₃-GaP₃ as a Promising Photocatalyst for Water Splitting

Photocatalytic water splitting to produce hydrogen is a potential means of achieving scalable and economically feasible solar hydrogen production. Two-dimensional (2D) triphosphides are 2D materials with potential applications in photovoltaics and optoelectronics. Here, we theoretically investigated 56 systems in total, including seven monolayer XP₃ (X = Al, Ga, Ge, As, In, Sn, and Sb) and their combined vertical and lateral heterostructures. We found that the lateral heterostructure AlP₃-GaP₃ should be a promising photocatalyst for water splitting, through a quadruple screening process combining free energy calculations. It is fascinating that AlP₃-GaP₃ ingeniously combines all the desired features for photocatalytic water-splitting reactions, including a nearly direct band gap (1.43 eV), perfect band edge position, high STH efficiency (16.89%), broad light absorption region of sunlight, ultrahigh carrier mobility (20,000 cm² V^-1 s^-1), low exciton binding energy (0.33 eV), and excellent stability in a water environment. Moreover, through Gibbs free energy calculations, the active sites and possible reaction pathways of the overall water-splitting reaction by AlP₃-GaP₃ were also confirmed. Our work offers a strategy for the design and fabrication of novel lateral heterostructures for a high-performance photocatalyst in water-splitting reactions.