Ni-Co nanosheets supported on conductive "core" for integrated supercapacitor with high performance

Highlights: • Hierarchical Ni-Co is fabricated by growing nanosheet on dispersive nanorod surface. • Nanosheets are benefit for ion adsorption/de-adsorption and surface redox reactions. • Interlayer Ni serves as current collector and electronic conductor. • Self-support Ni-Co electrode manifests high specific capacitance and good stability. - Abstract: Developing supercapacitors with high energy density, fast charging rates, and superior cycle life is crucial to the ever-increasing electric energy storage. However, how to construct a new type of supercapacitors involving pseudocapacitive performance and electric double-layer capacitive performance and exhibiting enhanced electronic conductivity is still challenging. Here, hierarchical Ni_xCo_2x(OH)_y@Ni@ZnO/ITO architecture is successfully fabricated by growing Ni_xCo_2x(OH)_y nanosheets on surface of well-aligned Ni@ZnO nanorod using co-electrodeposition method. Ni_xCo_2x(OH)_y with layered structure is wrapped like rippled silk and increases the specific surface area, which is crucial and benefit for fast ion adsorption/de-adsorption and fast surface redox reactions. Importantly, interlayer Ni serves as a nanostructured current collector and electronic conductor, playing an important role in rate capability. By virtue of structure features, the self-support Ni_xCo_2x(OH)_y@Ni@ZnO/ITO as binder-free electrode for supercapacitors manifests higher specific capacitance (124 mF cm⁻² at 0.1 mA cm⁻², the mass of active material per square centimeter is typically in 100s micrograms). Furthermore, the Ni_xCo_2x(OH)_y@Ni@ZnO/ITO exhibits remarkable cycling stability with about 95% specific capacitance retention after 5000 cycles. The results show that Ni-Co nanostructure constructed on surface of embedded conductive "core" materials is promising for high-energy supercapacitors.