A promising photocatalyst for water-splitting reactions with a stable sandwiched P₄O₂/black phosphorus heterostructure and high solar-to-hydrogen efficiency

Black phosphorus (BP) is a promising two-dimensional (2D) semiconductor, because of its tunable band gap and high hole mobility; however, its easy degradation under atmospheric conditions largely limits its application in photocatalytic water-splitting reactions. To overcome this disadvantage, we proposed a strategy for designing sandwiched P₄O₂-encapsulated BP (P₄O₂/BP) 2D materials, considering the automatic formation and high stability of P₄O₂ in air. We systematically considered five different packing models involving twenty sandwiched P₄O₂/BP systems using first-principles calculations. Through the triple screening process of 20 sandwiched P₄O₂/BP systems, we found that the O-1-P system with intrinsic electric field ingeniously combines all the desired features for photocatalytic water-splitting reactions, including small direct band gap (1.34 eV), low exciton binding energy, high hole mobility and ultrahigh solar-to-hydrogen efficiency as high as 22.77%. Through Gibbs free energy calculations, the active sites and possible reaction pathways of full water-splitting reactions were also confirmed. Our work offers useful guidance for designing and fabricating stable 2D materials with high performance for application in photocatalytic water-splitting reactions.