Modulating Inorganic Dimensionality of Ultrastable Lead Halide Coordination Polymers for Photocatalytic CO2 Reduction to Ethanol

Abstract

Lead halide hybrids have shown great potentials in CO₂ photoreduction, but challenging to afford C₂₊ reduced products, especially using H₂O as the reductant. This is largely due to the trade-off problem between instability of the benchmark 3D structures and low carrier mobility of quasi-2D analogues. Herein, the lead halide dimensionality of robust coordination polymers (CP) was modulated by organic ligands differing in a single-atom change (NH vs. CH₂), in which the NH groups coordinate with interlamellar [PbI₂] clusters to achieve the important 2D→3D transition. This first CP based on 3D cationic lead iodide sublattice possesses both high aqueous stability and a low exciton binding energy of 25 meV that is on the level of ambient thermal energy, achieving artificial photosynthesis of C₂H₅OH. Photophysical studies combined with theoretical calculations suggest the bridging [PbI₂] clusters in the 3D structure not only results in enhanced carrier transport, but also promotes the intrinsic charge polarization to facilitate the C-C coupling. With trace loading of Rh cocatalyst, the apparent quantum efficiency of the 3D CP reaches 1.4 % at 400 nm with a high C₂H₅OH selectivity of 89.4 % (product basis), which presents one of the best photocatalysts for C₂ products to date.

Keywords: CO2 conversion; coordination polymers; crystal engineering; metal–organic frameworks; photocatalysis.