Adsorption and electrostatic potentials at the electrochemical interface

Abstract

This paper explores adsorption in electrochemical systems. Part I reviews ways to quantify adsorption, the energetic considerations that make adsorption favorable or unfavorable, how to measure adsorption experimentally, and how it has previously been modeled using extensions of the Langmuir isotherm. At the end of Part I, a simple Monte Carlo model (MC) is applied to a very complex carbon dioxide reduction system to study competitive adsorption. This application of Monte Carlo simulations demonstrates the challenges of extracting meaningful parameters from empirically fitting MC simulations to isotherms derived from nanoparticle-enhanced Raman spectra.

Part II examines how adsorption influences the electrostatic potential in the electrochemical double layer using molecular dynamics simulations. Adding on to previous work from the Willard group, this chapter calculates how adsorbate polarity and coverage influences two characterizations of Coulombic interactions: the Poisson potential and the Madelung potential. Both potentials, while having different shapes as a function of distance from the electrode surface, exhibit strong sensitivity to water structure. At high coverage, adsorbates decrease the number of interfacial waters, shifts the position of the molecular layers of waters at the interface, and disrupts the water's orientational order. Lastly, cross-sections of the 3D Poisson potential parallel to the electrode surface reveal large heterogeneity in Poisson potential values as a result of adsorbates. This suggests that 1D electrostatic potential profiles are not enough to understand forces in the electrochemical double layer.