Unveiling Ionic/Electronic Contributions to the Potential Development of Electrical Double Layer Using XPS.

Area of Science:

• Materials Science
• Electrochemistry
• Surface Science

Background:

• Electrical double-layer (EDL) formation is crucial for electrochemical devices.
• Understanding ion dynamics at electrode-electrolyte interfaces is key for energy storage and sensing.
• Graphene's unique properties make it a promising material for advanced electrochemical applications.

Purpose of the Study:

• To investigate the dynamics of electrical double-layer formation on multilayered graphene electrodes.
• To utilize time-dependent X-ray photoelectron spectroscopy (XPS) as a chemical voltmeter for probing ionic liquid potentials.
• To analyze the influence of electrical biasing and circuit conditions on potential decay and polarity reversal.

Main Methods:

• Time-dependent X-ray photoelectron spectroscopy (XPS) was employed to monitor the O 1s peak of an ionic liquid.
• A coplanar-capacitor device with multilayered graphene electrodes was subjected to 2 V biasing cycles.
• Measurements were conducted under both shorted and open-circuit conditions to observe potential dynamics.

Main Results:

• XPS O 1s peak shifts directly correlated with the local electrical potential of the ionic liquid, validating XPS as a chemical voltmeter.
• Short-circuiting the device induced a sudden potential jump and polarity reversal, attributed to the nulling of the electronic potential component.
• Open-circuit measurements showed potential decays without polarity reversal, indicating distinct mechanisms for charge dissipation.
• Observed potential decays exhibited long and multiple time constants, consistent with ionic motion.

Conclusions:

• Time-dependent XPS is a powerful technique for real-time monitoring of electrical double-layer dynamics and interfacial potentials.
• The interplay between electronic and ionic motion dictates the observed potential behavior, including polarity reversal.
• The findings provide insights into the fundamental processes governing charge accumulation and dissipation at graphene-electrolyte interfaces.