Many important electrochemical processes occur within a few nanometers from the interface in the electrical double layer (EDL). Understanding the interfacial field, molecular orientation as well as their distance from charged surfaces is critical for designing chemical reactions taking place in EDL with applications in the battery sector, chemical sensing, and catalysis. Here we have used a vibrational probe molecule, 4-cyanophenol, in the aqueous solution (10mM) and monitored its nitrile frequency vibration as a function of applied potential near a gold surface. The applied potential range is between +1.0 V to -1.0 V, with a vibrational Stark shift of approximately<br/>5 cm<sup>-1</sup>/V observed. The direction and magnitude of the Stark shift reported in this work for 4-cyanophenol molecules are similar to those reported in the literature for tethered 4-mercaptobenzonitrile to the surface. Two key conclusions can be drawn from the observed data in this study. First, because the nitrile frequency shows a shift upon change in potential, 4-cyanophenol molecules must reside in the EDL in the potential ranges of +1.0 V to -1.0 V. Second, even at open circuit voltage, 4-cyanophenol exhibits a propensity for the metal surface, most likely due to adsorption via the  OH moiety.

Interaction of phenols with an electrified interface tracked with a vibrational probe

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ACS Fall 2022

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