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Electronic screening using a virtual Thomas–Fermi fluid for predicting wetting and phase transitions of ionic liquids at metal surfaces

Abstract

Of relevance to energy storage, electrochemistry and catalysis, ionic and dipolar liquids display unexpected behaviours—especially in confinement. Beyond adsorption, over-screening and crowding effects, experiments have highlighted novel phenomena, such as unconventional screening and the impact of the electronic nature—metallic versus insulating—of the confining surface. Such behaviours, which challenge existing frameworks, highlight the need for tools to fully embrace the properties of confined liquids. Here we introduce a novel approach that involves electronic screening while capturing molecular aspects of interfacial fluids. Although available strategies consider perfect metal or insulator surfaces, we build on the Thomas–Fermi formalism to develop an effective approach that deals with any imperfect metal between these asymptotes. Our approach describes electrostatic interactions within the metal through a ‘virtual’ Thomas–Fermi fluid of charged particles, whose Debye length sets the screening length λ. We show that this method captures the electrostatic interaction decay and electrochemical behaviour on varying λ. By applying this strategy to an ionic liquid, we unveil a wetting transition on switching from insulating to metallic conditions.

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Fig. 1: Electrostatic interactions in the vicinity of metal surfaces.
Fig. 2: Induced charges and screening at metallic surfaces.
Fig. 3: Screened electrostatic interactions through the use of a virtual TF fluid.
Fig. 4: Capacitive behaviour of virtual TF fluids.
Fig. 5: Capillary freezing at metallic surfaces.
Fig. 6: Wetting transition of ionic liquids at metal surfaces.

Data availability

All the relevant simulation input scripts are available in this repository: Schlaich, Alexander, 2021, ‘Simulation input scripts for “Electronic screening using a virtual Thomas-Fermi fluid for predicting wetting and phase transitions of ionic liquids at metal surfaces”’, https://doi.org/10.18419/darus-2115, DaRUS.

Code availability

Molecular simulations were performed using the open source package LAMMPS, stable release 7 August 2019, available under https://www.lammps.org/. Post-processing was performed in Python using our open source toolbox MAICoS (https://gitlab.com/maicos-devel/maicos/).

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Acknowledgements

We acknowledge V. Kaiser for his help with the TF model and computation time through CIMENT infrastructure (Rhône-Alpes CPER07_13 CIRA) and the Equip@Meso project (ANR-10-EQPX-29-01). We also acknowledge funding from the ANR project TAMTAM (ANR-15-CE08-0008-01). A.S. acknowledges funding from the DFG under Germany’s Excellence Strategy—EXC 2075–390740016 and SFB 1313 (project no. 327154368) and support by the Stuttgart Center for Simulation Science (SimTech).

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B.C., L.B. and A.S. conceived the research. A.S. carried out the molecular simulations with support from D.J. A.S., B.C. and L.B. analysed the data. A.S. and B.C. wrote the paper with input from all authors.

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Correspondence to Benoit Coasne.

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Peer review informationNature Materials thanks the anonymous reviewers for their contribution to the peer review of this work.

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Supplementary Information

Supplementary Figs. 1–13, Table 1, analytical treatment of the TF model and further detail on methods.

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Schlaich, A., Jin, D., Bocquet, L. et al. Electronic screening using a virtual Thomas–Fermi fluid for predicting wetting and phase transitions of ionic liquids at metal surfaces. Nat. Mater. 21, 237–245 (2022). https://doi.org/10.1038/s41563-021-01121-0

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