Recent advances and future perspectives in supercapacitor materials design and charge storage mechanisms

Electrochemical supercapacitors are important energy-storage devices for applications requiring rapid charge-discharge, high power delivery, and long cycle life. However, their relatively low energy density compared with batteries, together with limitations in material stability, electrolyte performance, and manufacturing scalability, continues to restrict their broader application. This review critically examines recent advances in supercapacitor materials design and charge-storage mechanisms, emphasizing the relationships among material structure, interfacial chemistry, electrochemical kinetics, and practical device performance. The fundamental mechanisms, including electric double-layer capacitance, pseudocapacitance, battery-type Faradaic storage, and mixed charge-storage behavior, are discussed to clarify their distinctions and implications for electrode classification. The review evaluates advances in carbon-based nanostructures, transition-metal compounds, conducting polymers, 2D materials, and metal-organic framework-derived architectures by active-site accessibility, electronic conductivity, ion transport, structural stability, and energy-power trade-offs. The review focuses on heteroatom doping, defect engineering, heterostructure formation, and interface optimization as strategies to improve electrochemical performance. The review further considers electrolyte chemistry, electrode matching, device architecture, and flexible and miniaturized configurations. We critically assess electrochemical measurements alongside ex situ, in situ, and operando characterization techniques, highlighting the need to distinguish electrochemical signatures from definitive mechanistic evidence. We examine density functional theory, molecular dynamics, and machine-learning approaches for their potential to accelerate materials discovery and establish structure-property relationships. Finally, we evaluate commercial applications, safety, cost, sustainability, and scale-up challenges. Progress toward practical supercapacitors will require integrated materials and device engineering, standardized full-cell testing, mechanistic validation under operating conditions, and scalable, environmentally responsible manufacturing.