Redox‐Active Planar Ge(IV)O ₄ Linkers in Covalent Organic Frameworks for Enhanced Anodic Na ⁺ Storage

Abstract

Abstract Covalent organic frameworks (COFs) for ion storage usually suffer from the employment of inactive linking units and intrinsically lower conductivity than 10 −6  S cm −1 , resulting in significant specific capacity loss. Developing COFs with redox‐active linkers in addition to the functional building blocks and highly intra‐layer conjugated electronic structure for enhanced conductivity is therefore crucial toward enhancing ion storage capacity. Herein, two dimensional (2D) phthalocyanine‐based (Pc‐based) COFs, GeO 4 ‐MPc‐COFs (M = Co, Ni, and Zn), with redox‐active Ge(IV)O 4 linkers and multiple active sites in the functional Pc building blocks were fabricated from octahydroxylphthalocyaninato metal complexes MPc(OH) 8 and GeO 2 . The planar arrangement of Ge(IV)O 4 moieties induces significantly p–π interaction between Ge(IV)O 4 moieties and Pc macrocycles, facilitating the delocalization of π electrons throughout the 2D networks of GeO 4 ‐MPc‐COFs and resulting in an impressive conductivity of 0.14–0.36 × 10 −2  S cm −1 . This, in combination with the reversible redox activity of Ge(IV)O 4 linkers and N‐rich Pc building blocks in the GeO 4 ‐MPc‐COFs, leads to outstanding anodic Na + storage performance with a high reversible specific capacity (607 mA h g −1 at 100 mA g −1 ) and excellent cycling stability (only 0.00057% capacity decay per cycle during 4,000 charge–discharge cycles at 5 A g −1 ), representing the thus far reported best performance.