Processes at metal - solution interfaces: models and simulations.

NOELIA LUQUE; ELIZABETH SANTOS; WOLFGANG SCHMICKLER; PAOLA QUAINO

Molecular Modeling of Corrosion Processes: Scientific Development and Engineering Applications

Wiley

Lugar: Weinheim; Año: 2015; p. 65 - 98

Metal - solution interfaces are of obvious importance to corrosion, but they are particularly difficult to model. By definition, the interface comprises that part of the system in which the intensive variables of the two adjoining phases differ from their respective bulk values, and even in concentrated solutions this implies a thickness of the order of 15 - 20 A. This is too large to be modeled solely by density functionaltheory (DFT), which surface scientists often use as a panacea for the metal - gas interface. In addition, the two adjoining phases are of very different nature: Metals are usually solid at ambient temperatures, and their properties do not differ too much from those at 0 K, so that DFT, or semi-empirical force fields like the embedded atom method, are good methods for their investigation. In contrast, the molecules insolutions are highly mobile, and thermal averaging is indispensable. Therefore, the two parts of the interface usually require different models, and an important part of the art consists in their combination. In spite of these inherent difficulties, much progress has been achieved during the last decade, not least due to the ever increasing powers of computers. In this chapter, we focus on two processes of relevance to corrosion, on which our own group has worked: surface mobility enhanced by an electric field or by co-adsorbed chlorine atoms, and hydrogen evolution on pure metals and nanostructures. Although the methods by which we treat these processes are rather different, they have in common that they consist of a combination of several techniques: DFT, force fields and kinetic Monte Carlo for surface mobility, quantum statistics and DFT for electron transfer and electrocatalysis. We believe that these methods can also be applied to other, as yet little explored areas of corrosion research.