Tailoring Layer Number of 2D Porphyrin-Based MOF Towards Photo-Coupled Electroreduction of CO 2

Inspired by the success of graphene, a series of single- or few-layer two-dimensional (2D) materials have been developed and applied in the past decade. Here, we report the successful preparation of monolayer and bilayer (two dimensional) 2D porphyrin-based metal organic frameworks (MOFs) by a facile solvothermal method. The structure transition from monolayer to bilayer drives distinct electronic properties and restructuring behaviors, which finally results in distinct catalytic pathways towards CO2 electrocatalysis. The monolayer favors CO2-to-C2 pathway due to the restructuring of Cu-O4 sites while CO and HCOO- are the major products over the bilayer. In photo-coupled electrocatalysis, Faradaic efficiency (FE) of C2 compounds shows a nearly 4-fold increase on the monolayer than that under dark condition (FEC2 increases from 11.9% to 41.1% at -1.4 V). For comparison, the light field plays a negligible effect on the bilayer. The light-induced selectivity optimization is investigated by experimental characterization and density functional theory (DFT) calculations. This work opens up a novel possibility to tune the selectivity of carbon products just by tailoring the layer number of 2D material.