In Situ Growth of 3D Hierarchical ZnO@Ni x Co1−x(OH) y Core/Shell Nanowire/Nanosheet Arrays on Ni Foam for High-Performance Aqueous Hybrid Supercapacitors

In this study, we designed and synthesized a novel battery-type electrode featuring three-dimensional (3D) hierarchical ZnO@Ni x Co 1− x (OH) y core/shell nanowire/nanosheet arrays arranged on Ni foam substrate via a two-step protocol including a wet chemical process followed by electro-deposition. We then characterized its composition, structure and surface morphology by X-ray diffraction, energy-dispersive X-ray spectrometry (EDS), X-ray photoelectron spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy, EDS elemental mapping. Our electrochemical measurements show that the ZnO@Ni 0.67 Co 0.33 (OH) y electrode material exhibited a noticeably high specific capacity of as much as 255 (mA·h)/g at 1 A/g. Additionally, it demonstrated a superior rate capability, as well as an excellent cycling stability with 81.6% capacity retention over 2000 cycles at 5 A/g. This sample delivered a high energy density of 64 W·h/kg and a power density of 250 W/kg at a current density of 1 A/g. With such remarkable electrochemical properties, we expect the 3D hierarchical hybrid electrode material presented in this work to have promising applications for the next generation of energy storage systems.