Modulating the Density of Catalytic Sites in Multiple-Component Covalent Organic Frameworks for Electrocatalytic Carbon Dioxide Reduction.

It is generally assumed that the more metal atoms in covalent organic frameworks (COFs) contribute to higher activity toward electrocatalytic carbon dioxide reduction (CO 2 RR) and hindered us in exploring the correlation between the density of catalytic sites and catalytic performances. Herein, we have constructed quantitative density of catalytic sites in multiple COFs for CO 2 RR, in which the contents of phthalocyanine (H 2 Pc) and nickel phthalocyanine (NiPc) units were preciously controlled. With a molar ratio of 1/1 for the H 2 Pc and NiPc units in COFs, the catalyst achieved the highest selectivity with a carbon monoxide Faradaic efficiency (FE CO ) of 95.37% and activity with a turnover frequency (TOF) of 4713.53 h -1 . In the multiple H 2 Pc/NiPc-COFs, the electron-donating features of the H 2 Pc units provide electron transport to the NiPc centers and thus improved the binding ability of CO 2 and intermediates on the NiPc units. The theoretical calculation further confirmed that the H 2 Pc units donated their electrons to the NiPc units in the frameworks, enhanced the electron density of the Ni sites, and improved the binding ability with Lewis acidic CO 2 molecules, thereby boosting the CO 2 RR performance. This study provides us with new insight into the design of highly active catalysts in electrocatalytic systems.