Ionic liquids (ILs) are salts that are in the liquid state at room temperature and exhibit physical properties, such as high ionic conductivity, high thermal stability and large electrochemical stability windows that are of interest for many electrochemical device applications. The characterization of the electrochemical double-layer at electrode-electrolyte interfaces includes the determination of the potential of zero charge (pzc). The pzc is defined as the electrode potential at which the surface charge of the metal is fully compensated by that of the electrolyte. Typically, in dilute aqueous electrolytes, the pzc ican be obtained from potential-dependent impedance measurements at different electrolyte concentrations, from which a minimum in the differential capacitance indicates the pzc. An alternate approach to determine the pzc at solid electrodes is to measure the accumulated charge during the formation of the double-layer upon contact of the electrode with the electrolyte (potential-controlled immersion measurements). We have employed the latter to determine the pzc at polycrystalline gold electrodes-ionic liquid interfaces. The integrated charge of each transient was taken at different time points, in order to establish the effects of slow interfacial processes on the determination of the pzc. We find that at short timescales (10–100 ms after immersion) the slope of the q vs. E plot is very close to the average differential capacitance obtained from impedance measurements, and suggest that within this timescale the extracted pzc is the potential of zero <i>free </i>charge (PZFC). However, at longer timescales (200 ms - 60 s), a slower process controls the measured charge and induces a shift of the pzc to negative potentials. Complementary impedance spectroscopy measurements suggest that it is a diffusion-limited process and, therefore, the pzc obtained at longer timescales is intepreted as a potential of zero<i> total </i>charge (PZTC).

Electrode-ionic liquids interfaces: Determination of the potential of zero charge and characterization of slower charging processes

255th National Meeting (2018)

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