Understanding the potential dependent behavior of adducts on the surface has possible applications in battery industry, chemical sensing, and catalysis. We investigated the potential dependent formation/dissociation of 4-mercaptopyridine (4-mcpy) and boron trifluoride (BF3) Lewis adduct on roughened gold surface using surface enhanced Raman scattering (SERS) under practical electrochemical conditions (+0.5 to -0.7 V). The C=C/C=N Raman band of 4-mcpy molecules adsorbed on the gold surface appears at around 1585 cm<sup>-1</sup>. This Raman band undergoes a blue shift (1650 cm<sup>-1</sup>) when 4-mcpy is coordinately bonded to BF3. We used this distinct frequency shift as a probe to differentiate between the 4-mcpy-BF3 adduct and 4-mcpy monolayer. We report evidence that the formation of adduct is spontaneous at open circuit potential, and demonstrates a great stability at positive potentials up to +0.5 V. However, at negative potentials starting from -0.2 V the dissociation of the Lewis adduct was observed, causing a red shift to the frequency of C=C/C=N Raman band. Our work seeks to clarify the physical processes underlying this observed behavior.

Potential dependent formation/dissociation of interfacial Lewis acid-base adducts on the gold surface probed by vibrational spectroscopy

ACS Spring 2022

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