Microstructural design of hybrid CoO@NiO and graphene nano-architectures for flexible high performance supercapacitors

We demonstrate the rational design and fabrication of CoO nano-architectures with different morphologies (sheet-like, petal-like and urchin-like) on flexible activated carbon textiles (ACTs) by simply changing the reactant concentration. We further unveiled that the electrochemical properties of CoO nanostructures are morphology-dependent. The specific capacitance increased exponentially with the surface/volume ratio of nanostructures. The architecture with a higher surface area exhibits better electrochemical performance. Due to its higher surface/volume ratio and better electrochemical performance, the urchin-like CoO nanostructure was further chosen as a backbone to deposit NiO nanoflakes to construct a hierarchical core/shell CoO@NiO hybrid nanostructure. Flexible ACTs wrapped with conductive graphene were used as a negative material. After coating with a PVA-KOH polymer gel which served as both the solid state electrolyte and separator, the flexible core/shell CoO@NiO/ACT//ACT/graphene asymmetric cell exhibited an exceptional combination of electrochemical properties in terms of working potential (1.6 V), energy density (52.26 W h kg^-1), maximum power density (9.53 kW kg^-1), and cycling stability (97.53% capacitance retention after 2000 cycles even under harsh working conditions). Such a hierarchical nanostructure on a cotton-enabled flexible textile substrate should find more applications in next-generation flexible solid-state power sources for future wearable electronic devices.