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Off-plane polarization in two dimensional materials is significant during the designation of functional nano-devices. As a prototype, the metal chalcogen-diphosphate CuInP 2 S 6 monolayer is selected, and the structure transition from the initial antiferroelectric (AFE) state to off-plane ferroelectric (FE) state is realized under the combined action of normal strain and electric field. With the introduce of compressed strain, the critical driven field for the transition is remarkably lowered, which is favorable for actual device operation and avoids the possible breakdown of film. As the compressed strain increases, the FE state changes to ground state, and the height of barrier between AFE state and FE state is lowered simultaneously. It is confirmed that the FE state keeps stable at room temperature even if the strain and the electric field are removed. Furthermore, the band gap of the monolayer changes from indirect to direct as the structure transition occurs, which will have potential photovoltaic applications. We hope our theoretical investigation can supply an alternative avenue to modify and improve the functionality of low-dimensional materials.

Developing robust, low-cost, and scalable catalysts for photoelectrochemical (PEC) water splitting devices is crucial for the sustainable hydrogen evolution reaction (HER). MoS 2 has emerged as a potent alternative to Pt-based catalysts for the HER. However, the active sites of 2H-MoS 2 are reported to locate at the edges, leaving a large number of inert basal planes useless. Herein, a facile strategy is reported to activate the MoS 2 basal plane via an in situ PEC protocol. Both experimental studies and theoretical calculations reveal the emergence of O−Mo−S sites on the MoS 2 basal planes, which enable not only enhancing its intrinsic conductivity but also modulating the adsorption behavior of H atoms and consequent HER activity. As a result, the MoS 2 -decorated Si photocathodes exhibit an applied bias photon-to-current efficiency of 4.9% under the simulated AM1.5G illumination. This study offers a potential scalable route for the fabrication of high-performance and precious metal-free solar-to-fuel devices.