Microscopic Structure of the Metal–Aqueous Electrical Double Layer

Determine the microscopic molecular-scale structure of the electrical double layer at metal–aqueous interfaces, resolving the specific interfacial details that are currently debated across experiments and simulations.

Background

In the discussion of ionic density profiles at Au(111) in aqueous electrolytes, the paper compares predictions from QM/DRISM, Poisson–Boltzmann models, and explicit molecular dynamics. Different studies report conflicting behavior for cation positioning (e.g., Na+ in the inner vs outer Helmholtz plane) and the role of interfacial hydrogen-bond network disruption under bias, while classical theory often expects small cations to remain fully solvated in the outer Helmholtz plane.

The authors show that DRISM results are highly sensitive to Lennard–Jones parameterization and mixing rules, and that pair-specific metal–ion parameters can qualitatively alter interfacial ion profiles and capacitance behavior. Given these discrepant observations and model sensitivities, they explicitly state that the microscopic structure of the electrical double layer at metal–aqueous interfaces is still not fully understood and that several details remain open for debate.

References

Considering the different observations and conclusions of the studies discussed above, the microscopic structure of the electrical double layer at metal-aqueous interfaces seems still not fully understood, and several details remain open for debate.

— Investigating the Electrochemical Double Layer with Quantum-Chemical Simulations and Implicit Solvation Models  (2603.29674 - Mangiameli et al., 31 Mar 2026) in Results and Discussion, Density Profiles → Ionic density profiles (Subsubsection); following discussion around Fig. 4

The chain-like hydrogen-bond topology found at negative electrode charge is potentially relevant to the cathodic regime of hydrogen evolution, but its role in proton-transfer pathways remains a hypothesis for future reactive simulations.

— Disentangling Surface Charge and Electrolyte Effects on Interfacial Water at Electrified Pt(111)  (2609.26685 - Eggert et al., 22 Sep 2026) in Section Conclusions

Combining HD-VSFG with temperature-jump or microcalorimetric measurements on the same electrode would therefore directly test whether the potentials of zero orientation and maximum entropy coincide, and thereby establish whether the PME can serve as a reliable proxy for interfacial water orientation.

— Interfacial Water Responds Linearly to Charge yet Is Charge-Asymmetric  (2610.09705 - Litman et al., 7 Oct 2026) in Discussion