Interfacial electronic tuning and polarization effects enhance Na⁺ ion storage performance of covalent organic frameworks with maximized active site loading on graphene

Covalent organic frameworks (COFs) with tunable redox sites are promising negative electrodes for supercapacitors (SCs) and capacitive deionization (CDI), but their application is limited by low capacity, slow kinetics, and unclear ion storage mechanisms. Here, we present a dual interface regulation strategy combining interfacial electronic structure tuning and polarization effects to boost Na⁺ storage in a 2D conjugated COF (TBHC-COF)/graphene composite (TBHCrGO). Dense active sites on the conjugated COF framework provide high pseudocapacitive Na⁺ storage, while interfacial π-π coupling with graphene increases electron density and accelerates charge transfer. Meanwhile, the interfacial polarization effect from strong electronic coupling improves Na⁺ storage stability and relieves structural stress during cycling. As a Na⁺ ion asymmetric SC negative electrode, TBHCrGO delivers an energy output of 56.4 Wh kg⁻¹ at 950 W kg⁻¹ with 95.0 % capacity retention over 50,000 cycles. In a hybrid CDI system, TBHCrGO achieves a high specific adsorption capacity of 87.5 mg g⁻¹ and excellent cycling stability over 100 desalination cycles without capacity loss. This work provides an effective interface engineering approach for designing high-performance COF-based electrodes for advanced energy storage and water treatment.