Subtle Tuning of Catalytic Well Effect in Phthalocyanine Covalent Organic Frameworks for Selective CO₂ Electroreduction into C₂H₄

Abstract In the electrocatalytic CO₂ reduction reaction (CO₂RR), the strategic design of a catalytic well capable of regulating the overall confinement effects of catalytic sites holds significant promise for enhancing multiple‐electron transfer and C─C coupling efficiency, particularly for the generation of C₂₊ products. Here, a series of Cu‐salphen‐based covalent organic frameworks (COFs) featuring hydroxyl‐induced catalytic well are synthesized, which demonstrate successful application in electrocatalytic CO₂RR to yield multiple‐electron transferred products. The meticulously engineered catalytic well, facilitated by multi‐hydroxyl groups, manifests robust confinement effects, facilitating selective adsorption, enrichment, and activation of CO₂, intermediate stabilization, and reduction of energy barriers for electrocatalytic CO₂RR. Specifically, product selectivity can be finely tuned from CH₄ to C₂H₄ by modulating the levels of catalytic well, with CuPc‐DFP‐4OH‐Cu exhibiting the most pronounced catalytic well effect, yielding a high 56.86% faradaic efficiency (FE) for C₂H₄ at −0.7 V, while CuPc‐DFP‐Cu, with the weakest catalytic well effect, achieves a 75.24% FE for CH₄ at −1.0 V. Notably, the attained FE for C₂H₄ (56.86%) surpasses that of all reported COFs to date. Complemented by theoretical calculations and in situ tests, this study delves deeply into the pivotal roles of hydroxyl‐induced catalytic well with confinement effects.