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Continuous transition from double-layer to Faradaic charge storage in confined electrolytes

Abstract

The capacitance of the electrochemical interface has traditionally been separated into two distinct types: non-Faradaic electric double-layer capacitance, which involves charge induction, and Faradaic pseudocapacitance, which involves charge transfer. However, the electrochemical interface in most energy technologies is not planar but involves porous and layered materials that offer varying degrees of electrolyte confinement. We suggest that understanding electrosorption under confinement in porous and layered materials requires a more nuanced view of the capacitive mechanism than that at a planar interface. In particular, we consider the crucial role of the electrolyte confinement in these systems to reconcile different viewpoints on electrochemical capacitance. We propose that there is a continuum between double-layer capacitance and Faradaic intercalation that is dependent on the specific confinement microenvironment. We also discuss open questions regarding electrochemical capacitance in porous and layered materials and how these lead to opportunities for future energy technologies.

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Fig. 1: Overview of electrochemical interfaces with varying degrees of electrolyte confinement.
Fig. 2: Examples of potential-dependent effects in carbon EDLCs.
Fig. 3: Cation intercalation into the hydrated interlayer of birnessite.
Fig. 4: Influence of the number of graphene layers on Li+ charge storage.
Fig. 5: Unified approach to charge storage in nanoconfined environments.

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Acknowledgements

P.T.C., J.W., Y.G. and V.A. acknowledge support from the Fluid Interface Reactions, Structures and Transport (FIRST) Center, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences at Oak Ridge National Laboratory under contract no. DE-AC0500OR22725 with UT Battelle, LLC. S.F. acknowledges funding from the German Federal Ministry of Education and Research (BMBF) in the ‘NanoMatFutur’ program (grant no. 03XP0423). S.F. and P.S. acknowledge support from the Agence Nationale de la Recherche (Labex STORE-EX) and P.S. from the ERC Synergy Grant MoMa-Stor no. 951513.

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Correspondence to Simon Fleischmann, Patrice Simon, Yury Gogotsi, Volker Presser or Veronica Augustyn.

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Fleischmann, S., Zhang, Y., Wang, X. et al. Continuous transition from double-layer to Faradaic charge storage in confined electrolytes. Nat Energy 7, 222–228 (2022). https://doi.org/10.1038/s41560-022-00993-z

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