Janus Zn-IV-VI: Robust Photocatalysts with Enhanced Built-In Electric Fields and Strain-Regulation Capability for Water Splitting.

The use of 2D materials to produce hydrogen (H 2 ) fuel via photocatalytic water splitting has been intensively studied. However, the simultaneous fulfillment of the three essential requirements-high photon utilization, rapid carrier transfer, and low-barrier redox reactions-for wide-pH-range production of H 2 still poses a significant challenge with no additional modulation. By employing the first-principles calculations, it has been observed that the Janus ZnXY 2 structures (X = Si/Ge/Sn, Y = S/Se/Te) exhibit significantly enhanced built-in electric fields (0.20-0.36 eV Å -1 ), which address the limitations intrinsically. Compared to conventional Janus membranes, the ductile ZnSnSe 2 and ZnSnTe 2 monolayers have stronger regulation of electric fields, resulting in improved electron mobility and excitonic nature (E binding = 0.50/0.35 eV). Both monolayers exhibit lower energy barriers of hydrogen evolution reaction (HER, 0.98/0.86 eV, pH = 7) and resistance to photocorrosion across pH 0-7. Furthermore, the 1% tensile strain can further boost visible light utilization and intermediate absorption. The optimal AC-type bilayer stacking configuration is conducive to enhancing electric fields for photocatalysis. Overall, Janus ZnXY 2 membranes overcome the major challenges faced by conventional 2D photocatalysts via intrinsic polarization and external amelioration, enabling efficient and controllable photocatalysis without the need for doping or heterojunctions.