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An Unsaturated Bond Strategy to Regulate Active Centers of Metal-Free Covalent Organic Frameworks for Efficient Oxygen Reduction
Summary:
The authors from Qingdao University and North University of China developed metal-free covalent organic frameworks (COFs) with unsaturated bonds for efficient oxygen reduction reaction (ORR), achieving high catalytic activity and stability in alkaline electrolyte.
Background:
1. To address the challenge of improving the performance of metal-free ORR catalysts, previous researchers have explored various strategies, including heteroatom doping and molecular structure optimization, achieving certain success. However, there are still issues such as relatively low activity and insufficient understanding of the role of unsaturated states.
2. The authors in this study proposed an innovative method by introducing unsaturated bonds (UBs) into COFs to regulate the electronic structure and enhance ORR performance, obtaining significant results.
Research Content:
1. Synthesis:
The authors synthesized Py-COF, Vinyl-COF, and Azo-COF using a condensation method with specific monomers and solvents.
2. Characterizations:
1) BET surface areas of the COFs are 535 m²g⁻¹ for Py-COF, 620 m²g⁻¹ for Vinyl-COF, and 800 m²g⁻¹ for Azo-COF, with pore sizes of 1.61 nm, 1.83 nm, and 1.89 nm, respectively.
2) SEM/TEM tests show the rod-like morphology of the COFs with a diameter of 200 nm.
3) UV/Vis DRS, PL emission spectra, and XPS were used to analyze the electronic structure and charge transfer properties.
3. Application:
The COFs were tested as ORR catalysts in 0.1 M KOH solution. Azo-COF exhibited the highest half-wave potential of 0.68 V vs. RHE and the smallest Tafel slope of 89 mVdec⁻¹.
4. Mechanism:
DFT calculations and in situ Raman spectra revealed that the unsaturated bonds induce local charge redistribution and enhance the affinity for oxygen intermediates, with the para C=N groups identified as active centers.
Outlook:
This research provides a novel strategy for designing metal-free COF catalysts by introducing unsaturated bonds, which significantly enhances ORR performance and offers insights for further development of efficient electrocatalysts.
An Unsaturated Bond Strategy to Regulate Active Centers of Metal-Free Covalent Organic Frameworks for Efficient Oxygen Reduction
Authors: Xiangyu Yan, Bingbing Wang, Jun Ren, Xiaojing Long, Dongjiang Yang
DOI: 10.1002/anie.202209583
Link: https://onlinelibrary.wiley.com/doi/10.1002/anie.202209583
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