Stable Na<sup>+</sup> Ion Storage via Dual Active Sites Utilization in Covalent Organic Framework‐Carbon Nanotube Composite
Anupam Dey, Atin Pramanik, S. P. Purohit, Sandip Biswas, Shreyasi Chattopadhyay, Tymofii S. Pieshkov, Gopalakrishnan Sai Gautam, Pulickel M. Ajayan, Tapas Kumar Maji
Abstract
Abstract Redox‐active covalent organic frameworks (COFs) with metal binding sites are increasingly recognized for developing cost‐effective, eco‐friendly organic electrodes in rechargeable energy storage devices. Here, we report a microwave‐assisted synthesis and characterization of a triazine‐based polyimide COF that features dual redox‐active sites (−C=O from pyromellitic and −C=N− from triazine) and COF@CNT nanocomposites ( COF@CNT‐X , where X=10, 30, and 50 wt % of NH 2 ‐MWCNT) formed through covalent linking with amino‐functionalized multiwalled carbon nanotubes. These composites are evaluated as cathode materials for the sodium‐ion batteries (SIBs). The amine functionalization renders the covalent bond between COF and CNT, improving electronic conductivity, structural rigidity, and long‐term stability. The interfacial growth of COF layers on CNTs increases accessible redox‐active sites, enhancing sodium diffusion kinetics during sodiation/desodiation. The COF@CNT‐50 composite exhibits outstanding Na + ion storage performance (reversible capacity of 164.3 mAh g −1 at 25 mA g −1 ) and excellent stability over 1000 cycles at ambient temperature. At elevated temperature (65 °C), it also maintains good capacity and cycle stability. Ex situ XPS analysis confirms the importance of dual active sites in the Na + diffusion mechanism. Density functional theory (DFT) calculations reveal insights into Na + binding sites and corresponding binding energies into COF structure, elucidating the experimental storage capacity and voltage profile.