The Influence of Water Vapor on the Electrochemical Shift of an Ionic Liquid Measured by Ambient Pressure X‐ray Photoelectron Spectroscopy

Abstract

Ionic liquids (ILs) are considered to be one of the steppingstones to fabricate next generation electrochemical devices given their unique physical and chemical properties. The addition of water to ILs significantly impact electrochemical related properties including viscosity, density, conductivity, and electrochemical window. Herein we utilize ambient pressure X‐ray photoelectron spectroscopy (APXPS) to examine the impact of water on values of the electrochemical shift (S), which is determined by measuring changes in binding energy shifts as a function of an external bias. APXPS spectra of C 1s, O 1s and N 1s regions are examined for the IL 1‐butyl‐3‐methylimidazolium acetate, [C4mim][OAc], at the IL/gas interface as a function of both water vapor pressure and external bias. Results reveal that in the absence of water vapor there is an IL ohmic drop between the working electrode and quasi reference electrode, giving rise to chemical specific S values of less than one. Upon introducing water vapor, S values approach one as a function of increasing water vapor pressure, indicating a decrease in the IL ohmic drop as the IL/water mixture becomes more conductive and the potential drop is driven by the electric double layer at the electrode/IL interface.

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

“…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.…”

In Situ Electrochemical XPS Monitoring of the Formation of Anionic Gold Species by Cathodic Corrosion of a Gold Electrode in an Ionic Liquid

“…The species in the bulk of the electrolyte ideally experience the full potential drop resulting in a −1.0 eV/V shift of the BE as for the species present. 36 In our case, the IL components reveal a ∼−0.9 eV/V slope.…”

Fe Powder Catalytically Synthesized C3N3 toward High-Performance Anode Materials of Lithium-Ion Batteries

“…Correspondingly, the high-resolution C 1s spectra of the three samples (Figures S6b, S7b, and S8b) also showed an extra C–N peak. In the meantime, the high-resolution O 1s spectra of the three samples (Figures S6d, S7d, and Figure S8d) also showed a second peak with a higher binding energy, which can be attributed to the adsorbed water. − The higher the reaction temperature of the sample, the stronger the intensity of this peak. It is because the increase of the specific surface areas and pores allows more water molecules to enter the sample.…”