Graphene and MoS2 interacting with water: a comparison by ab initio calculations

TL;DR

This study compares how graphene and MoS2 interact with water using ab initio calculations, revealing similar basal plane adsorption but significant differences at edges affecting their environmental stability and reactivity.

Contribution

The paper provides a detailed ab initio comparison of water interactions with graphene and MoS2, highlighting edge reactivity differences and their implications for material stability.

Findings

Similar water adsorption energies on basal planes of both materials

Graphene edges promote water splitting, unlike MoS2 edges

Water-driven oxidation of MoS2 is less favorable than adsorption

Abstract

Although very similar in many technological applications, graphene and MoS2 bear significant differences if exposed to humid environments. As an example, lubrication properties of graphene are reported to improve while those of MoS2 to deteriorate: it is unclear whether this is due to oxidation from disulfide to oxide or to water adsorption on the sliding surface. By means of ab initio calculations we show here that these two layered materials have similar adsorption energies for water on the basal planes. They both tend to avoid water intercalation between their layers and to display only mild reactivity of defects located on the basal plane. It is along the edges where marked differences arise: graphene edges are more reactive at the point that they immediately prompt water splitting. MoS2 edges are more stable and consequently water adsorption is much less favoured than in graphene. We also show that water-driven oxidation of MoS2 layers is unfavoured with respect to adsorption.