Nanoconfined Space: Revisiting the Charge Storage Mechanism of Electric Double Layer Capacitors

The electric double layer capacitor (EDLC) has been recognized as one of the most appealing electrochemical energy storage devices. Nanoporous materials with relatively high specific surface areas are generally used as the electrode materials for electric double layer capacitors (EDLCs). The past decades have witnessed anomalous phenomena of EDLCs under nanoconfined space, which to a large degree doubt the conventional recognition. However, there are currently still no deep insights and consensus on the mechanism of these striking discoveries. In this Perspective, we start with a brief introduction to contextualize the significance of EDLCs, especially with electrode materials of nanoconfined space. Next, we briefly review the landmark studies in light of the charge storage mechanism of EDLCs, mainly focusing on the study of nanoporous materials for EDLCs. Subsequently, we reexamine the basic concepts under nanoconfined space and some representative in situ characterization techniques applied to understand the charge storage mechanism of EDLCs. Finally, we provide general conclusions and insights into the future research directions in the field of EDLCs.