Recent advances in pseudocapacitive electrode materials for high energy density aqueous supercapacitors: Combining transition metal oxides with carbon nanomaterials

The demand for high-power and energy-dense electrochemical energy storage solutions has led to the utilization of pseudocapacitive materials. These materials store charges by undergoing Faradaic reactions at or near the electrode surfaces. They offer higher energy density than electric double-layer capacitors while maintaining the rapid charging/discharging capabilities characteristic of supercapacitors. This review delves into the synergistic relationship between transition metal oxides (TMOs) and carbon-based materials to create advanced supercapacitors. Combining the pseudocapacitive properties of TMOs with the high conductivity and carbon surface area, hybrid composites offer the potential to bridge the gap between energy and power density. The review comprehensively explores a range of TMOs, including ZnO, NiO, CoO, CuO, MnO₂, and RuO₂, and their integration with various carbon architectures. Key synthesis techniques, characterization methods, and electrochemical performance metrics are discussed to comprehensively understand these materials. Moreover, the review highlights recent advancements and identifies critical challenges to guide future research efforts toward developing high-performance and commercially viable supercapacitors based on TMO/carbon composites.