A First-Principles Study of the Reactivity and Layer-Dependent Properties of Phosphorene

Phosphorene exhibits promising tribological application due to its layered structure that imparts intrinsic lubricating properties. Understanding the mechanisms by which oxygen and other ambient species modify phosphorene remain a key challenge, with the impact of the layer thickness and point defects still unknown. Despite its potential as a solid-state lubricant, nanoscale insights into layer-dependent defect formation, surface reactivity and potential degradation remain limited. In particular, the multilayer-dependent degradation behaviour of phosphorene in the presence of common environmental species such as hydrogen (H), oxygen (O), and hydroxyl (OH) has received little attention. In this work, we perform a systematic density functional theory (DFT) investigation to explore how these chemical species interact with monolayer to 4-layer phosphorene, including systems with and without phosphorus vacancies. Our findings show that H adsorption is energetically favourable only in bilayer configurations, while O and OH show strong exothermic interactions across all thicknesses, regardless of the presence of defects, with the bilayer showing the most favourable interaction with these species. Structural responses, including changes in bond lengths and interlayer spacing, were quantified and found to depend on both the type of adsorbate and the number of layers. The presence of vacancies induces localized distortions but does not compromise the overall structural integrity. Overall, our results provide a detailed, layer-by-layer understanding of phosphorene's chemical reactivity in ambient environments and highlight the need to consider both layer number and intrinsic defects