Figure 3. Extrapolation of the potential drop functional dependency from the spectral broadening of pyrazine and water core levels.

Comparison between the experimental and simulated FWHM trends using the liquid phase pyrazine (LPPy) N 1s (a) and the liquid phase water (LPW) O 1s (b) peaks, as function of the applied potentials and for a KOH concentration of 0.4 mM (d_EDL=15.2 nm) (OCP, open circuit potential and FWHM, full-width at half-maximum); an evaluation of the statistical goodness of the fit through a chi-square analysis (χ²) is provided for the different electrochemical double layer (EDL) models and core levels used for the EDL probing (LPPy N 1s and LPW O 1s, respectively). The error bars were determined via repeated measurements of the FWHM of a given core level, propagated with the experimental spectral resolution (see Methods section).