Tuning Asymmetric Isomers in One-Dimensional Covalent Organic Frameworks to Enhance Oxygen Reduction Activity

Area of Science:

• Materials Science
• Catalysis
• Organic Chemistry

Background:

• Crystalline skeletons with embedded isomers can improve catalytic activity for oxygen reduction reaction (ORR).
• Research has primarily focused on symmetric molecules, leaving the study of asymmetric effects in isomeric systems challenging.
• Developing novel electrocatalysts requires understanding how molecular geometry influences reaction pathways.

Purpose of the Study:

• To investigate the impact of isomeric thiophene units on the ORR activity of one-dimensional covalent organic frameworks (COFs).
• To explore asymmetric design strategies for tuning molecular geometry and catalytic performance.
• To identify potential active sites and reaction mechanisms in these engineered COFs.

Main Methods:

• Synthesis of one-dimensional covalent organic frameworks (COFs) incorporating isomeric thiophene units (COF-α and COF-β).
• Electrochemical characterization to evaluate catalytic activity for oxygen reduction reaction (ORR).
• Theoretical calculations and in situ Attenuated Total Reflection Fourier-Transform Infrared Spectroscopy (ATR-FTIR) for mechanistic studies.

Main Results:

• Asymmetric thiophene isomers precisely adjusted intermediate adsorption and electronic states, leading to controllable chemical activity.
• The introduction of 2-substituted asymmetric thiophene units facilitated a hydrogen peroxide production pathway with high productivity (11.20 mol g_cat^-1 h^-1) and Faradaic efficiency (90.16%).
• Theoretical and experimental data identified the benzene ring carbon atom (site-8) adjacent to the thiophene unit as a potential active site, activated by the asymmetric skeleton.

Conclusions:

• Asymmetric geometric isomerism in COFs is an effective strategy for designing high-performance electrocatalysts.
• The study provides a novel approach for regulating catalytic activity through precise control of molecular geometry and electronic structure.
• This work advances the understanding of structure-activity relationships in COFs for ORR and related catalytic processes.