Evaluation of the Oxygen Reduction Reaction Electrocatalytic Activity of Postsynthetically Modified Covalent Organic Frameworks

Abstract

The pyrolysis of organic precursors to produce heteroatomic-doped carbonaceous materials has emerged as a powerful tool to construct metal-free heterogeneous electrocatalysts due to their low cost and their environmental friendliness. However, the lack of control in the atomic positions or the location of the chemical functionalities makes it difficult to establish structure–property relationships. Herein, we report an easy strategy to compare the electrocatalytic oxygen reduction reaction (ORR) performance of metal-free and nonpyrolyzed materials by postsynthetic modification of covalent organic frameworks (COFs) via click-chemistry. This method facilitates the evaluation of different active centers using materials with the same morphology and prevents active site agglomeration by covalently anchoring these moieties inside of a porous and crystalline framework. In this study we developed a series of diimide-based materials (XDI0.17-COFs) with a loading of 7.65 × 10–4 mol of active site/mg of host COF. The bulk COFs have been delaminated to perform electrode modification by drop-casting. The electrocatalytic response toward the ORR has been studied in alkaline media obtaining the best results for the NDI0.17-COF with an onset potential of 0.77 V (vs reversible hydrogen electrode, RHE) and a limiting current of 4.2 mA/cm2 by a preferred pathway toward water electroreduction. Finally, an adequate combination of density functional theory with the thermochemical Gibbs free energy formalism has been used to theoretically rationalize the ORR mechanism in these metal-free and nonpyrolyzed materials. We have obtained theoretical ORR overpotentials for each COF system agreeing with the experimental observation, which correlate with the ability of the NDI, BzDI, and PDI molecular blocks to accommodate electrons. Our work provides a guideline on how to study the electrocatalytic performance of different organic moieties in metal-free and non-pyrolyzed COFs avoiding their de novo synthesis by using the click postsynthetic methodology.

Experimentally revealed and theoretically certified synergistic electronic interaction of V-doped CoS for facilitating the oxygen evolution reaction

“…The rate-determining step (RDS) is the step with the largest Δ G n value for the four-electron process. 41 The free energy profiles of the OER on VCoS indicated that the RDS was the one-step formation of OOH*, with VCoS having a smaller Δ G n value of 1.57 eV compared to MoCoS (1.79 eV) (Fig. 3(b)), and the free energy value of CoS is 1.66 eV (Fig.…”

Advancements in two-dimensional covalent organic framework nanosheets for electrocatalytic energy conversion: current and future prospects

“…Zhang et al proposed an optimal transition metal for producing single-atom catalysts (SAC) with COFs. DFT calculations were performed in this study [129] . These calculations suggested that the transition metals bind to the N site, Ni, and Co, lowering the Gibbs energy barrier for the OER.…”

Covalent Organic Frameworks Based Electrocatalysts for Two-Electron Oxygen Reduction Reaction: Design Principles, Recent Advances, and Perspective

“…Typically, they possess precisely controllable monomers, large specific surface area, and high stability, which make them an efficient platform for electrocatalysis [ 27 , 28 , 29 ]. Specifically, the remarkable advantages of COFs have received widespread attention in electrocatalytic ORR [ 30 , 31 , 32 , 33 , 34 , 35 , 36 ]. The large specific surface area and porous nature of COFs can provide sufficient active sites to participate in the catalytic reaction [ 37 ].…”