High-performance hybrid supercapacitors based on self-supported 3D ultrathin porous quaternary Zn-Ni-Al-Co oxide nanosheets

Mixed transition metal oxides with hierarchical, porous structures, constructed from interconnected nano-building blocks, are considered promising positive electrodes for high-performance hybrid supercapacitors. Here we report our findings in design, fabrication, and characterization of 3D hierarchical, porous quaternary zinc-nickel-aluminum-cobalt oxide (ZNACO) architectures assembled from well-aligned nanosheets grown directly on nickel foam using a facile and scalable chemical bath deposition process followed by calcination. When tested as a binder-free electrode in a 3-electrode configuration, the ZNACO display high specific capacity (839.2 C g⁻¹ at 1 A g⁻¹) and outstanding rate capability (~82% capacity retention from 1 A g⁻¹ to 20 A g⁻¹), superior to those of binary-component NiCo₂O₄ and ZnCo₂O₄ as well as single-component Co₃O₄ electrode. More remarkably, a hybrid supercapacitor consisting of an as-fabricated ZNACO positive electrode and an activated carbon negative electrode exhibits a high energy density of 72.4 Wh kg⁻¹ at a power density of 533 W kg⁻¹ while maintaining excellent cycling stability (~90% capacitance retention after 10,000 cycles at 10 A g⁻¹), demonstrating a promising potential for development of high-performance hybrid supercapacitors. Further, the unique electrode architecture is also applicable to other electrochemical systems such as batteries, fuel cells, and membrane reactors.