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  • Open Access

Classical Theory of Electron-Ion Correlations at Electrochemical Interfaces: Closing the Circuit from Double-Layer Charging to Ion Adsorption

Nils Bruch1,2, Michael Eikerling1,2, and Tobias Binninger1,*

  • 1Theory and Computation of Energy Materials (IET-3), Institute of Energy Technologies, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
  • 2Chair of Theory and Computation of Energy Materials, Faculty of Georesources and Materials Engineering, RWTH Aachen University, 52062 Aachen, Germany

  • *Contact author: t.binninger@fz-juelich.de
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PRX Energy 5, 013009 – Published 3 March, 2026

DOI: https://doi.org/10.1103/65xq-svmf

Abstract

The electric double layer (EDL) that forms at the interface between metals and ionic solutions is at the heart of various energy technologies. Recent experimental data have challenged our traditional understanding of the EDL charging behavior, which is based on mean-field Gouy-Chapman-Stern-type (GCS) models. In this article, we present a classical theory for the EDL, derived from first-principles statistical mechanics, that accounts for electron-ion correlation effects using the method of image charges and systematically extends beyond the mean-field level. Such electron-ion correlations introduce an additional interaction between the metal surface and electrolyte ions, significantly altering the EDL structure. Our theory, valid in the limit of dilute electrolyte solutions and weakly charged metal surfaces, achieves quantitative agreement with experimental capacitance data across a wide range of electrode materials and electrolyte solvents, and thus resolves long-standing questions on the origin of discrepancies to GCS predictions. Thereby, the framework conceptually unifies the processes of double-layer charging and ion adsorption, which are typically considered as distinct phenomena, but are shown to be manifestations of the same fundamental electrostatic principles.

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Popular Summary

Charged interfaces between metal electrodes and electrolyte solutions are a hot topic in the electrochemical discourse, due to their ubiquitous importance for electrochemical energy technologies. The modern understanding of electrochemical charging phenomena is challenged by persistent discrepancies between experimental measurements and theoretical predictions of the interfacial capacitance. Standard theoretical models neglect an important class of phenomena, correlations between electronic and ionic charges, that are notoriously challenging to capture with theoretical descriptions. Building upon recent advances in field-theoretic approaches, this work presents a comprehensive framework that coherently incorporates electron-ion correlations into electrochemical interface models. The theory achieves quantitative agreement with experimental data on the interfacial charging characteristics for a variety of electrode-electrolyte systems, resolving long-standing puzzles in this field. The theory and the results obtained put a strong emphasis on the crucial role of interfacial correlations, representing a significant step towards a modern understanding of electrochemical charge storage and transfer processes.

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PRX Energy 5, 013009– Published 3 March, 2026
  • Received 25 July 2025
  • Revised 14 December 2025
  • Accepted 5 February 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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