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

It is generally assumed that the more metal atoms in covalent organic frameworks (COFs) contribute to higher activity toward electrocatalytic carbon dioxide reduction (CO₂RR) 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 CO₂RR, in which the contents of phthalocyanine (H₂Pc) and nickel phthalocyanine (NiPc) units were preciously controlled. With a molar ratio of 1/1 for the H₂Pc 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 H₂Pc/NiPc-COFs, the electron-donating features of the H₂Pc units provide electron transport to the NiPc centers and thus improved the binding ability of CO₂ and intermediates on the NiPc units. The theoretical calculation further confirmed that the H₂Pc 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 CO₂ molecules, thereby boosting the CO₂RR performance. This study provides us with new insight into the design of highly active catalysts in electrocatalytic systems.