Downsizing Covalent Organic Framework Catalysts for Electrochemical CO2 Reduction via Trityl-Protected Precursors

Kenichi Endo^a, Asif Raza^a^,^b, Liang Yao^a, Samuel Van Gele^a^,^c, Andrés Rodríguez-Camargo^a^,^d, Hugo Vigniolo-González^a^,^c^,^e, Lars Grunenberg^a^,^c, Bettina Lotsch^a^,^c^,^e

^aNanochemistry Department, Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany

^bPresent address: Bernal Institute, University of Limerick, V94 T9PX Limerick, Ireland

^cDepartment of Chemistry, Ludwig-Maximilians-Universität München, 81377 Munich, Germany

^dDepartment of Chemistry, University of Stuttgart, 70569 Stuttgart, Germany

^eCluster of excellence e-conversion, Lichtenbergstr. 4a, 85748 Garching, Germany

Materials for Sustainable Development Conference (MATSUS)
Proceedings of MATSUS23 & Sustainable Technology Forum València (STECH23) (MATSUS23)

#e-FuelSyn - Electrocatalysis for the Production of Fuels and Chemicals

VALÈNCIA, Spain, 2023 March 6th - 10th

Organizers: Carla Casadevall Serrano and Julio Lloret Fillol

Poster, Kenichi Endo, 333
Publication date: 22nd December 2022

Covalent organic frameworks (COFs), organic crystalline 2D or 3D polymers formed by reversible linkages, are promising electrocatalyst platforms owing to their high porosity, designability, and stability.[1] For example, cobalt-porphyrin-based COFs show high catalytic performance in the electrochemical CO2 reduction reaction (eCO2RR).[2] Recently, porphyrinoid-based COFs with various chemical structures have been developed as efficient CO2RR catalysts.[3] However, controlling the morphology of COF catalysts is a challenge, which can limit their electrocatalytic performance even if the chemical structure is optimally designed. Especially, the porphyrinoid COF precursors have low solubility, making it hard to synthesize COF CO2RR catalysts with controlled particle sizes.
In this work, we report a new synthetic methodology for downsized COF nanoparticle catalysts, which utilizes the trityl protection of amino groups. The method is inspired by the use of protecting groups in other COFs.[4,5] Trityl protection provides high solubility to a common cobalt porphyrin precursor, while its deprotection proceeds in situ under solvothermal COF synthesis conditions. This colloidal deprotection–polymerization process yields smaller COF nanoparticles than a conventional synthesis without compromising crystallinity and porosity. The resulting COF nanoparticles exhibit superior performance in eCO2RR, with a 10-fold increase in CO production rate, higher faradaic efficiency, and higher stability compared to conventional COF particles with the same chemical structure. The improved performance can be attributed to better mass transport as well as electron transport from electrodes to COF active sites. This study provides new insights and a strategy for the preparation of COF electrocatalysts with controlled morphology and enhanced performance.

References:

[1] Zhao, X.; Pachfule, P.; Thomas, A., Covalent organic frameworks (COFs) for electrochemical applications. Chem. Soc. Rev. 2021, 50, 6871-6913.

[2] Lin, S.; Diercks, C. S.; Zhang, Y. B.; Kornienko, N.; Nichols, E. M.; Zhao, Y.; Paris, A. R.; Kim, D.; Yang, P.; Yaghi, O. M.; Chang, C. J., Covalent organic frameworks comprising cobalt porphyrins for catalytic CO2 reduction in water. Science 2015, 349, 1208-13.

[3] Huang, S.; Chen, K.; Li, T.-T., Porphyrin and phthalocyanine based covalent organic frameworks for electrocatalysis. Coord. Chem. Rev. 2022, 464.

[4] Vitaku, E.; Dichtel, W. R., Synthesis of 2D Imine-Linked Covalent Organic Frameworks through Formal Transimination Reactions. J. Am. Chem. Soc. 2017, 139 (37), 12911-12914.

[5] Zhao, Y.; Guo, L.; Gandara, F.; Ma, Y.; Liu, Z.; Zhu, C.; Lyu, H.; Trickett, C. A.; Kapustin, E. A.; Terasaki, O.; Yaghi, O. M., A Synthetic Route for Crystals of Woven Structures, Uniform Nanocrystals, and Thin Films of Imine Covalent Organic Frameworks. J. Am. Chem. Soc. 2017, 139 (37), 13166-13172.

Acknowledgements:

K.E. acknowledges postdoctoral scholarships from the Max Planck Society and the Alexander von Humboldt Foundation. The authors acknowledge financial support from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation, Project-ID 358283783, SFB 1333), the Max Planck Society, the Center for NanoScience, the DFG cluster of excellence “e-conversion” (EXC 2089/1–390776260), and the Bavarian Research Network SolTech.

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