Interfacial electric field competition in strain-modulated MoSTe/Hf2CO2: Inducing a direct-Z scheme charge transfer pathway for overall water splitting

Abstract

The key to high-performance photocatalysts is efficient charge separation and easy regulation. A two-dimensional (2D) MoSTe/Hf2CO2 heterojunction has been proposed using density-functional theory (DFT), and the charge transfer path of the direct-Z scheme has been realized in the presence of strain. Importantly, the MoSTe/Hf2CO2, with its abundant tunability, is able to effectuate the transition from Type–II–A → Type-I → Type–II–B → direct Z-scheme → Type-III. In particular, under +2% and +3% biaxial strains, the band gaps of MoSTe/Hf2CO2 heterojunction are 0.335 and 0.024 eV, respectively, smaller than those of conduction band offset (CBO) and valence band offset (VBO), which favors the recombination of interlayer carriers and thus the formation of direct Z-scheme heterojunctions. While the charge transfer at the interface is subjected to two interfacial electric fields (IEF), IEFMoSTe and IEFInterface, which have obvious competition, the tensile strain leads to the enhancement of the interlayer coupling, which in turn strengthens the competitive advantage of the IEFInterface of the heterojunction. Moreover, the Gibbs free energy in hydrogen evolution reaction (HER) of the MoSTe/Hf2CO2 at a strain of +3% is very near to 0, meeting the requirements for an ideal photocatalyst. In this study, not only is a high-performance direct-Z scheme photocatalyst that can undergo overall water splitting proposed but also the abundant tunability of this heterojunction will have great application prospects in optoelectronic devices.