(178c) Ion Adsorption and Electrode-Electrolyte Interfacial Structure Effects On Oxygen Adsorption

The accurate representation of electrode potential variation, interfacial electric fields, and interfacial solvation is challenging within density functional theory (DFT) models. Accurate evaluation of elementary electrocatalytic reaction step energetics requires models to evaluate electrode and electrolyte effects and the dependence of kinetics on electrode potential. Several approaches have been developed to model the electrical double layer using first-principles methods. The first model is a typical vacuum slab calculation with the linear dependence of electron energy on potential. An external, homogeneous electric field model provides a computationally inexpensive model of an electrified interface, but correlation to a specific electrode potential is unclear. A third model directly controls the electrode potential by charging the aqueous electrochemical system. These models will be compared in their evaluation of the impact of electrode potential variation on molecular oxygen adsorption to the solvated Pt(111) surface, of relevance to the oxygen reduction reaction within a proton exchange membrane fuel cell (PEMFC).

The interfacial water structure affects the binding strength and extent of charge transfer for molecular oxygen adsorbed on the Pt(111) surfaces. In a PEMFC, the electrolyte consists of hydrated Nafion ionomers. The presence of other adsorbing species may alter electronic interactions and affect the adsorbed oxygen state. We use solvated sulfate groups as our electrolyte, and investigate the influence of ion adsorption on oxygen adsorption. Three electrochemical models will be use to differentiate the importance of local electric field, through surface and through space interactions, coadsorption, and solvent effects, especially ion adsorption.