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Tapping into Charge Storage with Operando-XPS Using a Multi-Layer Graphene Coplanar Capacitor and an Ionic Liquid
Ezgi Kutbay1, Merve Taner Camci2, Burak Ulgut1
1Department of Chemistry, Bilkent Univeristy, Ankara 06800, Turkey.
Langmuir : the ACS Journal of Surfaces and Colloids
|May 26, 2026
Summary
Bias-induced electrosorption of ions on graphene electrodes alters surface potential. Increased Rubidium cation (Rb+) concentration enhances conductivity and creates bias asymmetry in ionic liquid electrolytes.
Area of Science:
- Surface Science
- Electrochemistry
- Materials Science
Background:
- Electrified interfaces are crucial in electrochemical devices.
- Understanding ion behavior at electrode surfaces is key to optimizing performance.
- Graphene electrodes offer unique properties for interfacial studies.
Purpose of the Study:
- To investigate surface population and electrical potentials on graphene electrodes under bias using X-ray Photoelectron Spectroscopy.
- To analyze the electrosorption dynamics of ions from an ionic liquid solution.
- To correlate ion dynamics with changes in conductivity and interfacial properties.
Main Methods:
- X-ray Photoelectron Spectroscopy (XPS) was employed to analyze surface composition.
- Graphene electrodes were studied in contact with an ionic liquid (TFSI-, DEME+, Rb+).
- Electrical bias was applied to induce and monitor ion electrosorption and its effects.
Main Results:
- Ion enrichment (electrosorption) at the graphene/vacuum interface was observed with increasing bias.
- Binding energies shifted due to bias and ion screening effects.
- Rubidium cation (Rb+) population increased, while DEME+ decreased, maintaining electroneutrality.
- Induced currents increased significantly, driven by mobile Rb+ cations, leading to bias-dependent asymmetry.
Conclusions:
- Electrosorption dynamics significantly influence surface composition and electrical properties of graphene electrodes.
- The balance of anions and cations at electrified interfaces is critical for understanding their behavior.
- These findings provide insights into the structure and dynamics of ionic liquids at electrode surfaces.
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