π‐Sticked Metal‒Organic Monolayers for Single‐Metal‐Site Dependent CO₂ Photoreduction and Hydrogen Evolution Reaction

Abstract Hierarchical self‐assembly of 2D metal‒organic layers (MOLs) for the construction of advanced functional materials have witnessed considerable interest, due to the increasing atomic utilizations and well‐defined atom‒property relationship. However, the construction of atomically precise MOLs with mono‐/few‐layered thickness through hierarchical self‐assembly process remains a challenge, mostly because the elaborate long‐range order is difficult to control via conventional noncovalent interaction. Herein, a quadruple π‐sticked metal‒organic layer (πMOL) is reported with checkerboard‐like lattice in ≈1.0 nanometre thickness, on which the catalytic selectivity can be manipulated for highly efficient CO₂ reduction reaction (CO₂RR) and hydrogen evolution reaction (HER) over a single metal site. In saturated CO₂ aqueous acetonitrile, Fe‐πMOL achieves a highly effective CO₂RR with the yield of ≈3.98 mmol g^‒1 h^‒1 and 91.7% selectivity. In contrast, the isostructural Co‐πMOL as well as mixed metallic FeCo‐πMOL exhibits a high activity toward HER under similar conditions. DFT calculations reveal that single metal site exhibits the significant difference in CO₂ adsorption energy and activation barrier, which triggers highly selective CO₂RR for Fe site and HER for Co site, respectively. This work highlights the potential of supramolecular π^…π interaction for constructing monolayer MOL materials to uniformly distribute the single metal sites for artificial photosynthesis.