Engineering Rich-Cation Vacancies in CuCo2O4 Hollow Spheres with a Large Surface Area Derived from a Template-Free Approach for Ultrahigh Capacity and High-Energy Density Supercapacitors

Intriguing cationic defects with hollow nano-/microstructures are a critical challenge but a potential strategy to discover electrochemical energy conversion and storage devices with improved electrochemical performances. Herein, we successfully produced a highly porous, and large surface area of self-templated CuCo₂O₄ hollow spheres (CCOHSs) with cationic defects via a solvothermal route. We hypothesized that the inside-out Ostwald ripening mechanism of the template-free strategy was the framework for forming the CCOHSs. Cationic defects (Cu) within the CCOHSs were identified by employing various analytical techniques, including energy-dispersive X-ray spectroscopy analysis of both scanning and transmission electron microscopy, X-ray photon spectroscopy, and inductively coupled plasma-atomic emission spectroscopy. The resulting CCOHSs had significant properties, such as a high specific surface area of 98.32 m² g^-1, rich porosity, and battery-type electrode behavior in supercapacitor applications. Notably, the CCOHSs demonstrated an outstanding specific capacity of 1003.7 C g^-1 at 1 A g^-1, with excellent structural integrity and cycle stability. Moreover, the fabricated asymmetric CCOHS//activated carbon device exhibited a high energy density of 65.2 Wh kg^-1 at a power density of 777.8 W kg^-1.