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.