Enrichment effects of ionic liquid mixtures at polarized electrode interfaces monitored by potential screening

Shin, Sunghwan; Greco, Francesco; Maier, Florian; Steinrück, Hans‐Peter

doi:10.1039/d0cp04811a

Cited by 7 publications

(4 citation statements)

References 57 publications

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“…That experimental setup enabled the formation of a liquid film thin enough to probe the IL/electrode interface such that the authors were able to follow the EDL processes by tracing the shifts in the core-level binding energies under bias. While the application of direct current (DC) bias during XPS data acquisition provides steady-state information, demonstrated by us and others as well, − our group has previously shown that alternating current (AC) excitation is indispensable for investigation of the dynamics of electrical potential developments. − Use of scanning electron microscopy (SEM) for detecting similar changes due to potential induced intensity modulations was also recently reported by us . Both our XPS and SEM investigations revealed that the effects of time-resolved polarization of the metal electrodes can be followed locally up to extremely long-distance (centimeters) and long-time (hundreds of seconds) ranges, in a chemically specific fashion.…”

Section: Introductionsupporting

confidence: 58%

Assessing Local Electrical Properties of Ionic Liquid/Metal Interfaces with Operando-XPS and by Incorporating Additional Circuit Elements

Karaoglu,

Kutbay,

Ince

et al. 2023

Anal. Chem.

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X-ray photoelectron spectroscopy (XPS) has been utilized to record binding energy changes upon applying direct current (DC) and/or alternating current (AC) (square-wave) bias with different frequencies on a coplanar capacitor, having an ionic liquid (IL) film as the electrolyte. Electrical potential developments in numerous locations on the device are extracted from the variations in binding energy positions of the atomic core levels, which together with electrochemical measurements are used to extract local information before and after insertion of additional resistors in series. The presence of the IL introduces complex charging/discharging processes with a direct influence on the electrical double layer (EDL) formation, some of which can be untangled from each other via AC modulation by choosing appropriate time windows of observation. Accordingly, under 10 kHz modulation, fast processes are sampled, which are associated with electronic currents, and effects of slow migratory currents can be measured using 0.1 Hz. The addition of serial resistors allows us to quantify AC currents passing through, which reveals the magnitude of the system's impedance under different conditions. This process surprisingly reverses differences(s) in the voltage developments between the low and high frequencies over the electrified electrodes compared to those over the porous membrane in between. Our approach turns XPS into a powerful electrical and surface-sensitive tool for extracting localized electrochemical properties in a noninvasive and direct way. We expect that a wider utilization of the technique will lead to better identification of the obstacles for developing the next-generation sensing, energy harvesting, and storage systems as well as devices for iontronic/neuromorphic applications.

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Section: Introductionsupporting

confidence: 58%

Assessing Local Electrical Properties of Ionic Liquid/Metal Interfaces with Operando-XPS and by Incorporating Additional Circuit Elements

Karaoglu,

Kutbay,

Ince

et al. 2023

Anal. Chem.

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“…Ionic liquids are excellent candidates as new non-aqueous electrolytes that can be used in fuel cells, capacitors and batteries. 72 Since typical by-products of ionic liquid synthesis are halides and metal salts that interfere dramatically with the electrochemical properties of the molten salt, 73 the use of the halide-free and metal-free dialkylcarbonate route is particularly suited to the preparation of ionic liquids for these applications.…”

Section: Potential Uses Of the Dialkyl Carbonate Routementioning

confidence: 99%

The dialkylcarbonate route to ionic liquids: purer, safer, greener?

et al. 2023

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“…To investigate the fundamentals of these processes, researchers have used techniques such as electrochemical methods, microscopy, terahertz imaging, and X-ray analysis, − often complemented by modeling and simulations. , Still, every technique has its own shortcomings when it comes to replicating real-world electrochemical devices. Another tool often utilized for deeper insight is X-Ray Photoelectron Spectroscopy (XPS). − Over the course of several years, our research group has harnessed the power of XPS to delve into the intricate details of ionic liquid/metal interfaces. XPS, renowned for its exceptional surface sensitivity, enables us to unravel some of the chemical and electronic properties of the samples and/or devices.…”

Section: Introductionmentioning

confidence: 99%

AC-Modulated XPS Enables to Externally Control the Electrical Field Distributions on Metal Electrode/Ionic Liquid Devices

Kutbay,

Ince,

Suzer

2024

J. Phys. Chem. B

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X-Ray Photoelectron Spectroscopy (XPS) has been utilized to extract local electrical potential profiles by recording core-level binding energy shifts upon application of the AC [square-wave (SQW)] bias with different frequencies. An electrochemical system consisting of a coplanar capacitor with a polyethylene membrane (PEM) coated with the Ionic Liquid (IL) N,N-diethyl-Nmethyl-N-(2-methoxyethyl) ammonium bis(trifluoromethanesulfonyl)imide (DEME-TFSI) as the electrolyte is investigated. Analyses are carried out in operando, such that XPS measurements are recorded simultaneously with current measurements. ILs have complex charging/discharging processes, in addition to the formation of Electrical Double Layers (EDL) at the interfaces, and certain properties of these processes can be captured using AC modulation within appropriate time windows of observation. Herein, we select two frequencies, namely, 10 kHz and 0.1 Hz, to separate effects of the fast polarization and slow migratory motions, respectively. Moreover, the local potential developments after adding two equivalent series resistors at three different physical positions of the device have been carefully evaluated from the binding energy shifts in the F 1s peak representing the anion of the IL. This circuit modification allows us to quantify the AC currents passing through the device, as well as the system's impedance, in addition to revealing the potential variations due the IR drops. The complex AC-modulated local XPS data recorded can also be faithfully reproduced using the unmodulated F 1s spectrum and by convoluting it with electrical circuit output provided by the LT-Spice software. The outcome of these efforts is a more realistic equivalent circuit model, which can be related to chemical/physical makeup of the electrochemical system. An important finding of this methodology emerges as the possibility to induce additional local electrical field developments within the device, the directions of which can be reversed controllably.

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Enrichment effects of ionic liquid mixtures at polarized electrode interfaces monitored by potential screening

Abstract: The interface of electrodes and IL mixtures has been studied by in situ XPS. We found that the concentration of counterions at the interface can strongly deviate from the bulk composition due to interactions between electrode and IL.

Cited by 7 publications

References 57 publications

Assessing Local Electrical Properties of Ionic Liquid/Metal Interfaces with Operando-XPS and by Incorporating Additional Circuit Elements

Assessing Local Electrical Properties of Ionic Liquid/Metal Interfaces with Operando-XPS and by Incorporating Additional Circuit Elements

The dialkylcarbonate route to ionic liquids: purer, safer, greener?

AC-Modulated XPS Enables to Externally Control the Electrical Field Distributions on Metal Electrode/Ionic Liquid Devices

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