Exploring chemical speciation at electrified interfaces using detailed continuum models.

Abstract

We present a local free-energy functional-based generic continuum model for material interfaces with a specific emphasis on electrified solid/liquid interfaces. The model enables a description of multicomponent phases at interfaces and includes the effects of specific non-electrostatic interactions (specific adsorption), ion size disparity, and the explicit presence of neutral species. In addition to the optimization of electrostatic, non-electrostatic, and steric forces, the model can be easily modified to explore the effects of other channels for equilibration, including local chemical transformations driven by equilibrium constants and electrochemical reactions driven by the electrode potential. In this way, we show that, upon accounting for these effects, local speciation in the vicinity of the interface can be drastically different from what is expected from restricted models and minor species (from the bulk perspective) may become dominant due to the effects of local pH. We evaluate the ionic contribution to the surface tension at the interface and show how this could impact the structure of air/liquid interfaces. On the same footing, an attempt to describe electrochemical metal dissolution is made. The model allows estimates of the mutual population of newly produced ions depending on their charge and size and could be useful for interpretation of electrochemical and spectroscopic measurements if the dissolution involves different metal ions (species). With these advances, the proposed model may be used as an ingredient within a hybrid ab initio-continuum methodology to model biased interfaces.