Modulating the D-π-A Interactions in Metal-Covalent Organic Frameworks for Efficient Electroreduction of CO into Formate.

Crystalline porous framework materials have attracted tremendous interest in electrocatalytic CO reduction owing to their ordered structures and high specific surface areas as well as rich designability, however, still suffer from a lack of accuracy in regulating the binding strength between the catalytic sites and intermediates, which is crucial for optimizing the electrocatalytic activity and expanding the product types. Herein, we report three new kinds of vinylene-linked metal-covalent organic frameworks (TMT-CH-MCOF, TMP-CH-MCOF and TMP-MCOF) with continuously tunable D-π-A interactions by adjusting the structure of the monomers at the molecular level for realizing efficient electroreduction of CO to formate for the first time. Interestingly, compared with TMT-CH-MCOF and TMP-MCOF, the TMP-CH-MCOF exhibited the highest HCOO Faradaic efficiency (FE) of 95.6 % at -1.0 V vs RHE and displayed the FE above 90 % at the voltage range of -1.0 to -1.2 V vs. RHE, which is one of the highest among various kinds of reported electrocatalysts. Theoretical calculations further reveal that the catalytic sites in TMP-CH-MCOF with unique moderate D-π-A interactions have suitable binding ability towards the reaction intermediate, which is beneficial for the formation of *HCOO and desorption of *HCOOH, thus effectively promoting the electroreduction of CO to formate.