Modulation of Hydroxy Functionalities in Covalent Organic Frameworks for Efficient Oxygen Reduction Reaction

ABSTRACT

Metal‐free catalysts are gaining increasing interest for the electrochemical oxygen reduction reaction (ORR) due to their lower cost and functionality‐dependent catalytic performance. However, controlled functionalization and establishing a clear functional‐to‐property relationship in Metal‐free heteroatom‐doped carbon‐based electrocatalysts (CMFEs) is a daunting challenge. It's also vague how much functional group (heteroatom) incorporation in CMFEs is required to achieve optimal ORR activity. Here, we utilize a hydroxy‐functionalized covalent organic framework (COF) as a predesignable, highly functionalizable platform for establishing a clear functional‐property correlation for the electrochemical ORR reaction. We observe that the incorporation of hydroxy functionalities into imine COF is highly beneficial in enhancing the ORR activity with an increase in onset potential (E _onset )and half‐wave potential (E _1/2 ). Control over the number of hydroxy (‐OH) functionalities is highly essential for achieving optimal ORR activity. Among the various synthesized COFs, dihydroxy‐functionalized DATB‐COF displays the highest onset potential (0.96 V vs. RHE) and a half‐wave potential (E _1/2 ) value (0.71 V vs. RHE). Hydroxy functional group incorporation generates multiple catalytically active centers (C _O and C _N ) in COFs and makes ORR reaction kinetics more favorable by facilitating the formation of *OOH reaction intermediates.