Deconvoluting the Convoluted: Structural Ramifications of Postsynthetic Linkage Modification in COF-366-Co Catalysts

Postsynthetic modification (PSM) is a powerful strategy for modifying properties such as pore environment, stability and catalytic activity in covalent organic frameworks (COFs). While the chemical outcomes of PSMs are well documented, their impact on the underlying crystal lattice is rarely quantified. Yet, when translating modified COF systems toward catalytic applications, such structural changes can impact performance. In this work we interrogate precisely that blind spot for the benchmark electrocatalyst COF-366-Co. We apply three chemical PSM routes to the imine backbone: (i) quinoline cyclization (q-COF-366-Co), (ii) amine reduction (r-COF-366-Co), and (iii) nitrone oxidation (o-COF-366-Co) and investigate chemical as well as structural modifications induced by the functionalization. The catalysts are further investigated toward the electrochemical carbon dioxide reduction reaction in an attempt to decouple the multitude of convoluted aspects that affect catalytic activity, stability and selectivity such as particle size, disorder, strain, catalytic environment, and framework stability. Among the series, q-COF-366-Co showed a higher stability toward CO selectivity over time compared to the pristine COF-366-Co at -0.88 V vs reversible hydrogen electrode (RHE). Investigating q-COF-366-Co further showed, however, that higher functionalization concentrations led to simultaneous increase in disorder and a lower selectivity toward CO during catalysis. This indicates that a balance must be found between functionalization and preservation of crystalline lattice, offering insights into the design importance of maintaining structural coherence when comparing COF-based materials toward applications.