Multi-channel ion transport in COF/CRO sandwich films for flexible micro-supercapacitors

Abstract Covalent organic framework (COF) heterostructure films integrate diverse components with complementary merits, exhibiting remarkable synergistic effects for advanced flexible micro-supercapacitors (MSCs). However, ion transport and accessibility, especially at the alternately stacked 2D interface are compromised by the restacking of layers, which degrades electrochemical performances. Herein, we propose a stable sandwich-type heterostructure by intercalating a homogeneous and loosely packed 0D conjugated reticular oligomer (CRO) layer between 2D COF nanofilms. Size-controllable CRO layer effectively suppress COF layers restacking and regulate the interlayer spacing. The heterostructure significantly improves active site accessibility and creates multiple ion transport pathways, thereby facilitating ion transport while maintaining excellent mechanical flexibility. The optimized COF HP -CRO TT -COF HP electrode delivers a high H + diffusion coefficient ( D’ H + ) of 6.94 × 10 − 13 cm 2 /s at 0.1 V, showing a specific capacitance of 652.5 µF/cm 2 (10 mV/s) that is 1.4 times that of the CRO HP -COF TT -CRO HP counterpart. Finite element simulation and density functional theory (DFT) calculations further confirm that the CRO layers serve as a multifunctional module, providing abundant active sites, shortening ion diffusion pathways, and establishing efficient mult-channel ion transport networks. The MSC-COF HP -CRO TT -COF HP demonstrates outstanding mechanical durability, retaining over 95.01% of its performance after 10,000 bending cycles, and shows scalability for production in both series and parallel configurations.