Flexible asymmetric supercapacitors made of 3D porous hierarchical CuCo2O4@CQDs and Fe2O3@CQDs with enhanced performance

Highlights: • Both 3D porous CuCo₂O₄@CQDs and Fe₂O₃@CQDs ave been synthesized through CQDs-induced self-assembly technique. • CQDs could tune the morphology of products, and improve the performances. • Both CuCo₂O₄@CQDs and Fe₂O₃@CQDs electrodes display high capacitance and excellent rate capability. • The flexible device delivers high energy density and power density, good flexibility, and long cycling lifespan. Flexible asymmetric supercapacitors (FASCs) have attracted increasing interest in portable and wearable electronics. The practical application of FASCs in high energy density devices is limited by their low specific capacity, which can be effectively addressed by designing electrode materials hierarchically on the micro-nanoscale. Herein, well-defined 3D porous hierarchical CuCo₂O₄@carbon quantum dots (CQDs) and Fe₂O₃@CQDs architectures are rationally synthesized through a simple CQDs-induced hydrothermal self-assembly technique. Both of the as-prepared CuCo₂O₄@CQDs and Fe₂O₃@CQDs electrodes exhibit improved specific capacity, desirable rate capability and complementary potential range. A FASC (CuCo₂O₄@CQDs//Fe₂O₃@CQDs) on graphite paper delivers a high operation voltage of 1.55 V, an energy density of 39.5 Wh kg⁻¹ at 1203.7 W kg⁻¹, and long cycling lifespan. The excellent performance is ascribed to the good electronic conductivity with the assistance of CQDs and their unique 3D mesoporous structures with extraordinary specific surface area, which could provide fruitful active sites for electrochemical reactions. The newly developed FASC based on the Faradaic-type electrodes is inspiring, and would be promising for the applications in wearable electronic devices.