Rational design of hierarchically porous NiCo2O4 and Bi2O3 nanostructure: Anchored on 3D nitrogen doped carbonized melamine foam for flexible asymmetric supercapacitor

Recent advances in high-performance flexible energy storage devices require the development of electrode materials with optimized structure and composition. In this paper, we report the design and facile synthesis of 1D NiCo2O4 nanoneedle arrays (NiCo2O4-NNAs) and 2D Bi2O3 nanosheets arrays (Bi2O3-NSAs) on highly conductive 3D carbonized melamine foam (cMF), and explore their practical application as freestanding electrode materials for flexible asymmetrical supercapacitor. The resultant NiCo2O4-NNAs wrapped cMF ([email protected]2O4-NNAs) and Bi2O3-NSAs wrapped cMF ([email protected]2O3-NSAs) electrodes, which in unique pine branch-like and tremella-like structure, integrate the advantages of hierarchically porous structure as well as Faraday capacitance of metal oxide species and the double layer capacitance of cMF, and therefore exhibit high structural stability, large surface area, fast electron transport and ion diffusion characteristics, which give rise to a significant improvement of the supercapacitive performance. Consequently, the flexible asymmetric all-solid-state supercapacitor assembled with [email protected]2O4-NNAs as positive electrode, [email protected]2O3-NSAs as negative electrode and PVA/KOH as gel electrolyte demonstrates wide working voltage up to 1.5 V, a high energy density of 0.49 mWh/cm3 at the power density of 3.77 mW/cm3. In addition, the specific capacitance retention remains about 83.2% after 6000 cycles. Hence, we envision that the proposed asymmetric supercapacitor holds great promise for fulfilling the demanding applications in energy storage device.