Fabrication of Azacrown Ether-Embedded Covalent Organic Frameworks for Enhanced Cathode Performance in Aqueous Ni-Zn...

Crown ethers (CEs), known for their exceptional host-guest complexation, offer potential as linkers in covalent organic frameworks (COFs) for enhanced performance in catalysis and host-guest binding. However, their highly flexible conformation and low symmetry limit the diversity of CE-derived COFs. Here, we introduce a novel C₃-symmetrical azacrown ether (ACE) building block, tris(pyrido)[18]crown-6 (TPy18C6), for COF fabrication (ACE-COF-1 and ACE-COF-2) via reticular synthesis. This approach enables precise integration of CEs into COFs, enhancing Ni²⁺ ion immobilization while maintaining crystallinity. The resulting Ni²⁺-doped COFs (Ni@ACE-COF-1 and Ni@ACE-COF-2) exhibit high discharge capacity (up to 1.27 mAh ⋅ cm^-2 at 8 mA ⋅ cm^-2) and exceptional cycling stability (>1000 cycles) as cathode materials in aqueous alkaline nickel-zinc batteries. This study serves as an exemplar of the seamless integration of macrocyclic chemistry and reticular chemistry, laying the groundwork for extending the macrocyclic-synthon driven strategy to a diverse array of COF building blocks, ultimately yielding advanced materials tailored for specific applications.