Highly Efficient Photocatalytic CO₂ Reduction in Two-Dimensional Ferroelectric CuInP₂S₆ Bilayers

Photocatalytic CO₂ conversion into reproducible chemical fuels (e.g., CO, CH₃OH, or CH₄) provides a promising scheme to solve the increasing environmental problems and energy demands simultaneously. However, the efficiency is severely restricted by the high overpotential of the CO₂ reduction reaction (CO₂RR) and rapid recombination of photoexcited carriers. Here, we propose that a novel type-II photocatalytic mechanism based on two-dimensional (2D) ferroelectric multilayers would be ideal for addressing these issues. Using density-functional theory and nonadiabatic molecular dynamics calculations, we find that the ferroelectric CuInP₂S₆ bilayers exhibit a staggered band structure induced by the vertical intrinsic electric fields. Different from the traditional type-II band alignment, the unique structure of the CuInP₂S₆ bilayer not only effectively suppresses the recombination of photogenerated electron-hole (e-h) pairs but also produces a sufficient photovoltage to drive the CO₂RR. The predicted recombination time of photogenerated e-h pairs, 1.03 ns, is much longer than the transferring times of photoinduced electrons and holes, 5.45 and 0.27 ps, respectively. Moreover, the overpotential of the CO₂RR will decrease by substituting an S atom with a Cu atom, making the redox reaction proceed spontaneously under solar radiation. The solar-to-fuel efficiency with an upper limit of 8.40% is achieved in the CuInP₂S₆ bilayer and can be further improved to 32.57% for the CuInP₂S₆ five-layer. Our results indicate that this novel type-II photocatalytic mechanism would be a promising way to achieve highly efficient photocatalytic CO₂ conversion based on the 2D ferroelectric multilayers.