With the rapid improvement of the global economy, the role of energy has become even more vital in the 21st century. In this regard, energy storage/conversion devices have become a major, worldwide research focus. In response to this, we have prepared two-dimensional (2D)-hierarchical sheet-like ZnCo₂O₄ microstructures for supercapacitor applications using a simple hydrothermal method. The 2D-hierarchical sheet-like morphologies with large surface area and smaller thickness enhanced the contact area of active material with the electrolyte, which increased the utilization rate. We investigated the electrochemical performance of sheet-like ZnCo₂O₄ microstructures while using Cyclic voltammetry (CV), Galvanostatic charge-discharge (GCD), and Electrochemical impedance spectroscopy (EIS) analysis. The electrochemical results demonstrated that the ZnCo₂O₄ electrode possesses 16.13 mF cm⁻² of areal capacitance at 10 µA cm⁻² of current density and outstanding cycling performance (170% of capacitance is retained after 1000 cycles at 500 µA cm⁻²). The high areal capacitance and outstanding cycling performance due to the unique sheet-like morphology of the ZnCo₂O₄ electrode makes it an excellent candidate for supercapacitor applications.

The demand for eco-friendly renewable energy resources as energy storage and management devices is increased due to their high-power density and fast charge/discharge capacity. Recently, supercapacitors have fascinated due to their fast charge–discharge capability and high-power density along with safety. Herein, the authors present the synthesis of 3D-hierarchical peony-like ZnCo₂O₄ structures with 2D-nanoflakes by a hydrothermal method using polyvinylpyrrolidone. The reaction time was modified to obtain two samples (ZCO-6h and ZCO-12h) and the rest of the synthesis conditions were the same. The synthesized structures were systematically studied through various techniques: their crystalline characteristics were studied through XRD analysis, their morphologies were inspected through SEM and TEM, and the elemental distribution and oxidation states were studied by X-ray photoelectron spectroscopy (XPS). ZCO-12h sample has a larger surface area (55.40 m²·g⁻¹) and pore size (24.69 nm) than ZCO-6h, enabling high-speed transport of ions and electrons. The ZCO-12h electrode showed a high-specific capacitance of 421.05 F·g⁻¹ (31.52 C·g⁻¹) at 1 A·g⁻¹ and excellent cycle performance as measured by electrochemical analysis. Moreover, the morphologic characteristics of the prepared hierarchical materials contributed significantly to the improvement of specific capacitance. The excellent capacitive outcomes recommend the 3D-ZnCo₂O₄ hierarchical peony-like structures composed of 2D-nanoflakes as promising materials for supercapacitors with high-performance.

The need for efficient and sustainable energy storage has driven the development of hybrid supercapacitors (HSCs). These devices combine capacitive and battery-type electrodes to deliver high energy and power densities. Designing advanced battery-type electrode materials is crucial for meeting industrial requirements for next-generation devices. Bimetallic spinel cobaltites (MCo ₂ O ₄ ; M = Mn, Fe, Ni, Cu, Zn, and Mg) are promising options. They provide high theoretical capacity, multiple redox-active sites, and robust structural stability. Recent studies have focused on various strategies to enhance performance. These include elemental doping, controlling morphology, direct growth on conductive substrates, and forming binary or ternary composites with carbon materials, metal oxides or sulfides, layered double hydroxides, conducting polymers, and emerging two-dimensional (2D) or framework materials. Understanding how structure influences performance is key to optimizing charge storage and electron transport. This review highlights progress in designing spinel cobaltite-based battery-type materials for HSCs, with an emphasis on strategies that boost electrochemical performance. It specifically highlights studies reporting on the specific capacity (C g⁻ ¹ or mAh g⁻ ¹ ), as this metric directly reflects the practical application of these materials in energy storage devices. The review also discusses the main challenges and future research directions for industrial translation and scalable development of advanced battery-type electrodes for high-performance HSCs. Graphical abstract Advances in performance-enhancement strategies for bimetallic spinel cobaltites (MCo ₂ O ₄ , M = Mn, Fe, Ni, Cu, Zn, Mg) as battery-type electrodes in hybrid supercapacitors. The diagram highlights key approaches, including morphology engineering, elemental doping, conductive substrate integration, carbon-based composites, metal oxide/sulfide and ternary composites, conducting polymer composites, and advanced 2D/framework materials, emphasizing the structure–property–performance relationship for optimized electrochemical behavior.