Multifunctional Carbon Dots for Electrochemical Capacitors Reviewed: Their Opportunities and Challenges

Electrochemical capacitors (ECs) are promising energy storage devices due to their rapid charge/discharge capability. However, they face limitations in energy density, and certain capacitor materials may exhibit poor conductivity and structural instability. Carbon dots (CDs), characterized by their small size, abundant surface functional groups, and controllable properties, show great potential in enhancing the performance of ECs. This review presents the challenges and opportunities associated with multifunctional CDs in ECs. It begins by summarizing the classification and basic working principles of ECs. Next, it discusses in detail the synthesis methods, fundamental physical and chemical properties, and the electrochemical and photoelectrochemical properties of CDs. Subsequently, it explores the application of CDs as electrode additives and electrolyte additives in ECs, highlighting their unique benefits in improving capacitor performance. Additionally, it examines the innovative use of CDs in photo-assisted capacitors, revealing insights into capacitor technology derived from the synergistic effects of light and electrochemical energy storage processes. Finally, the current challenges facing the applications for CD-based ECs are discussed, followed by proposing future research opportunities. This review emphasizes the significant role of multifunctional CDs and their promising potential in advancing EC technology.