Delocalization-Driven Activation of Inert Imine Linkages in Covalent Organic Frameworks for Reversible Magnesium...

Area of Science:

• Materials Science
• Electrochemistry
• Organic Chemistry

Background:

• Imine-linked covalent organic frameworks (COFs) are explored as cathodes for rechargeable magnesium batteries (RMBs).
• The imine linkages (C═N) in COFs are typically electrochemically inert, limiting their application in energy storage.
• Redox inactivity is attributed to insufficient π-electron delocalization within the imine bonds.

Purpose of the Study:

• To investigate the electrochemical activity of imine linkages in COFs for RMBs.
• To demonstrate that enhancing local π-electron delocalization can transform inert imine bonds into active redox centers.
• To establish π-delocalization engineering as a strategy for activating inert bonds in energy storage materials.

Main Methods:

• Synthesized a triazine-based COF with precise fluorine substitution to engineer localized π-delocalization.
• Investigated the electrochemical behavior of the modified COF using electrochemical techniques.
• Performed theoretical calculations to understand the electronic structure and Mg2+ diffusion pathways.

Main Results:

• Fluorine substitution induced localized π-delocalization, activating the imine linkages.
• Activated imine sites facilitated reversible C═N ⇄ C-N⁻ conversion, a novel redox function in RMBs.
• Mg2+ diffusion barrier was halved, and the transport pathway shifted to the imine sites.
• The optimized COF cathode achieved a high specific capacity (203.6 mAh g⁻¹), excellent rate capability, and long-term cycling stability (72.9% retention after 9000 cycles).

Conclusions:

• π-delocalization engineering is an effective strategy to unlock latent redox functions in imine-based COFs.
• Activated imine linkages serve as efficient Mg2+ migration channels, significantly improving battery performance.
• This approach provides a mechanistic blueprint for activating inert bonds in organic frameworks for multivalent energy storage systems.