DFT Modeling of Stark-Tuning Effect: CO on Polarized Pd(100) as a Probe for Double-Layer Electrostatic Effects in Electrochemistry

Abstract

The lifetime of chemisorbed radical anions produced in the electroreduction of vinylic molecules is thought to play a decisive part in the mechanism accounting for the production of grafted films in electropolymerization reactions. With the ultimate purpose of evaluating these lifetimes, we propose a one-dimensional model taking into account the interface bond, the anion/metallic surface image charge potential, and the anion/polarized-surface electrostatic repulsion. Orders of magnitude are known for the parameters entering in these terms, except for the latter. In the present work, this term is described using the Gouy-Chapmann model for the electrochemical double layer. Comparing our theoretical DFT predictions on Stark-Tuning effect of CO on Pd(l00) with experiment, we can discuss on the legitimacy of a phenomenological linear relationship between the (microscopic) surface electric field and the (macroscopic) electrode potential. The slope of this relationship, termed the electric field rate, in (V.cm⁻¹),V⁻¹, turns out to be numerically equivalent to the characteristic length of the double layer, whatever the underlying model. Our calculated rates, carried out within the Gouy-Chapmann approximation, are in acceptable agreement with previous experimental estimates. First insights into our electropolymerization reactions suggest that the presumed intermediate chemisorbed radical-anions may have a borderline stability, i.e. a largely non negligible lifetime on the surface.