Supramolecularly Built Local Electric Field Microenvironment around Cobalt Phthalocyanine in Covalent Organic Frameworks for Enhanced Photocatalysis

Abstract

The local electric field (LEF) plays an important role in the catalytic process; however, the precise construction and manipulation of the electric field microenvironment around the active site remains a significant challenge. Here, we have developed a supramolecular strategy for the implementation of a LEF by introducing the host macrocycle 18-crown-6 (18C6) into a cobalt phthalocyanine (CoPc)-containing covalent organic framework (COF). Utilizing the supramolecular interaction between 18C6 and potassium ion (K⁺), a locally enhanced K⁺ concentration around CoPc can be built to generate a LEF microenvironment around the catalytically active Co site. The COF with this supramolecularly built LEF realizes an activity of up to 7.79 mmol mmol_Co^–1 h^–1 in the photocatalytic CO₂ reduction reaction (CO₂RR), which is a 180% improvement compared to its counterpart without 18C6 units. The effect of LEF can be subtly controlled by fully harnessing the K⁺@18C6 interaction by changing the potassium salts with different counterions. In situ spectroscopy and density functional theory calculations show that the complexation of K⁺ by 18C6 creates a positive electric field that stabilizes the critical intermediate *COOH involved in CO₂RR, which can be tuned by the halide ion-mediated K⁺@18C6 interaction and hydrogen-bonding interaction, consequently leading to improved catalytic performance to varying degrees.