Polarization-Driven Control of Dynamically Tunable Solar-to-Hydrogen Conversion and On-Demand Water Splitting in 2D Janus-Ferroelectric Heterojunctions

van der Waals heterostructures improve carrier efficiency via band engineering and interfacial design, surpassing traditional photocatalytic material limitations. However, their intrinsic electric fields are limited by work function differences, and carrier accumulation weakens field effects. Two-dimensional ferroelectric heterostructures leverage spontaneous polarization and dynamic tunability to optimize carrier transport and photocatalytic water-splitting kinetics. This study combines Janus MSSe (M = W, Mo) with α-In₂Se₃ monolayers to create a spontaneously polarized heterojunction. Through polarization switching (P↑ or P↓) and the synergistic effects of interlayer polarization and built-in electric fields, band alignment and carrier transport are regulated. In α-In₂Se₃/MSSe (M = W, Mo), P↓ suppresses photogenerated carrier migration, reducing the solar-to-hydrogen (STH) efficiency, while P↑ accelerates it, boosting the STH efficiency. Furthermore, introducing vacancies and adjusting polarization enable flexible regulation of reaction efficiency and controllable initiation and termination of water-splitting reaction. Our work introduces a novel methodology for controlling the dynamics of photogenerated carriers through the application of polarization-induced electric fields, thereby advancing the practical implementation of polarized photocatalysts in sustainable energy production and environmental remediation technologies.