Direct Spectroscopic Measurement of Interfacial Electric Fields near an Electrode under Polarizing or Current-Carrying Conditions

Abstract

Interfacial electric fields and the related molecular polarization are the central quantities that govern charge transfer between an electrode and a molecule. The presence of the interfacial field is often inferred indirectly through transport and capacitance measurements. It is desirable to measure such fields directly via the Stark shift that they induce on molecular vibrations. We report the Stark shift of a well-known vibrational chromophore tethered near an electrochemical interface measured using vibrational sum frequency generation spectroscopy. We have two important findings. First, we observe that the measured local field scales with respect to the ionic concentration in the electrolyte according to a model that combines the Gouy–Chapman theory with the capacitive response of a molecular layer. This behavior holds over 3 orders of magnitude in ionic concentration, therefore lending support to the validity of the model. Our results along with this model allow for estimation of the electric field n...