π-Sticked Metal-Organic Monolayers for Single-Metal-Site Dependent CO 2 Photoreduction and Hydrogen Evolution Reaction.

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 CO 2 reduction reaction (CO 2 RR) and hydrogen evolution reaction (HER) over a single metal site. In saturated CO 2 aqueous acetonitrile, Fe-πMOL achieves a highly effective CO 2 RR 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 CO 2 adsorption energy and activation barrier, which triggers highly selective CO 2 RR 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.