Redox-Active Planar Ge(IV)O₄ Linkers in Covalent Organic Frameworks for Enhanced Anodic Na⁺ Storage

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Covalent organic frameworks (COFs) often use inactive linkers, limiting conductivity (< 10⁻⁶ S cm⁻¹) and causing capacity loss in ion storage applications.
• Enhanced conductivity and redox activity in COFs are crucial for improving ion storage performance.

Purpose of the Study:

• To develop novel 2D phthalocyanine-based COFs (Pc-based COFs) with redox-active linkers for superior ion storage.
• To investigate the relationship between electronic structure, conductivity, and electrochemical performance in these new COFs.

Main Methods:

• Fabrication of 2D GeO₄-MPc-COFs (M = Co, Ni, Zn) using octahydroxylphthalocyaninato metal complexes and GeO₂.
• Characterization of the electronic structure and conductivity of the synthesized COFs.
• Electrochemical testing for sodium-ion (Na⁺) storage performance, including capacity, rate capability, and cycling stability.

Main Results:

• Achieved significantly enhanced conductivity (0.14–0.36 × 10⁻² S cm⁻¹) due to p-π interactions and delocalized π electrons in the GeO₄-MPc-COFs.
• Demonstrated outstanding anodic Na⁺ storage with a high reversible specific capacity of 607 mA h g⁻¹ at 100 mA g⁻¹.
• Exhibited excellent cycling stability with minimal capacity decay (0.00057% per cycle) over 4,000 cycles at 5 A g⁻¹.

Conclusions:

• The developed GeO₄-MPc-COFs, featuring redox-active Ge(IV)O₄ linkers and N-rich Pc units, offer exceptional ion storage capabilities.
• The enhanced conductivity and redox activity are key factors driving the superior electrochemical performance.
• These findings represent a significant advancement in COF design for high-performance energy storage applications.