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[4KT-Tp COF] Skeleton Engineering of Isostructural 2D Covalent Organic Frameworks for Energy Storage
Summary:
The authors from Tianjin University developed a series of isostructural 2D covalent organic frameworks (COFs) with orthoquinone redox-active sites, achieving high capacitances and excellent rate capabilities in the application of energy storage.
Background:
1. To address the problem of low capacitance and poor rate ability in COF-based electrodes, previous researchers have incorporated various redox-active groups into COFs, achieving some success. However, challenges remain in fully utilizing the redox-active sites and optimizing the material structure for better performance.
2. The authors in this work proposed an innovative skeleton engineering strategy by stepwise introduction of ketone groups to the skeletons of isostructural 2D COFs, obtaining enhanced capacitances and rate capabilities.
Research Content:
1. Synthesis:
The authors synthesized the KT-Tp COFs using the solvothermal Schiff-base condensation method.
2. Characterizations:
1) BET surface areas were 996 m² g⁻¹ for 1KT-Tp COF, 1402 m² g⁻¹ for 2KT-Tp COF, and 672 m² g⁻¹ for 4KT-Tp COF. Pore size distributions were centered on 2.49 nm for 1KT-Tp COF, 2.24 nm for 2KT-Tp COF, and 2.17 nm for 4KT-Tp COF.
2) SEM/TEM tests show the particle size of the material and reveal that 1KT-Tp COF and 2KT-Tp COF adopted fibrillar morphology with large aspect ratio, while 4KT-Tp COF exhibited short rod-like structure.
3) Electrochemical tests showed that 2KT-Tp COF and 4KT-Tp COF exhibited high capacitances of 256 and 583 F g⁻¹, respectively, at a discharge rate of 0.2 A g⁻¹.
3. Application:
The material was tested in asymmetric supercapacitor devices, and the 4KT-Tp COF//AC device achieved a maximum energy density of 12.5 W h kg⁻¹ with the power density of 240 W kg⁻¹ under the current density of 0.8 A g⁻¹.
4. Mechanism:
The analysis of the experimental results indicated that the orthoquinone moieties rendered enhanced performance than the redox COFs with isolated carbonyl groups. The pseudocapacitance percentages for 4KT-Tp COF and 2KT-Tp COF were extraordinary, achieving as high as 82% and 63%, respectively, at the scan rate of 10 mV s⁻¹.
Outlook:
This research demonstrates an effective skeleton engineering strategy for designing high-performance organic electrode materials by incorporating highly reversible redox-active orthoquinone sites, which greatly enhances the capacitive performance and opens a new avenue for the development of advanced COF-based energy storage materials.
Skeleton Engineering of Isostructural 2D Covalent Organic Frameworks: Orthoquinone Redox-Active Sites Enhanced Energy Storage
Authors: Miao Li, Jingjuan Liu, Yusen Li, Guolong Xing, Xiang Yu, Chengxin Peng, Long Chen
DOI：10.31635/ccschem.020.202000257
Link：https://www.ccschemistry.org/article/doi/10.31635/ccschem.020.202000257
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