Highly Localized Charges of Confined Electrical Double‐Layers Inside 0.7‐nm Layered Channels

Abstract A confined electrical double‐layer (EDL) inside nanoporous electrodes has a large capacitance and deviates from traditional ones. Unfortunately, its capacitive mechanism is still unclear. Herein, expanded vertical graphene/diamond (EVG/D) films with regular and ordered 0.7‐nm layered channels are designed and synthesized to serve as an ideal model for understanding confined EDL. A clear overall picture of confined EDL is provided at an atomic resolution with the aid of in situ electrochemical Raman spectroscopy, electrochemical quartz crystal microbalance (EQCM), and density functional theory (DFT) calculations combined with three‐dimension reference interaction site method (3D‐RISM). It is especially interesting that the induced charges in electrode hosts are highly localized with a density far higher than that on a traditional EDL and even close to those of ion batteries. It is proposed that such a high localization of induced charges plays an essential role in the high energy storage efficiency of confined EDL capacitance. This work not only provides a previously unexplored way to refine the mechanism of confined EDL, but also further lays the foundation for understanding the functions of nanoporous or layered materials in electrochemical energy storage.