Modulating the Band Gaps, Binding Energetics, and Diffusion Kinetics of Black and Blue Phosphorene via K+ Adsorption: A DFT Study

Abstract

Two-dimensional (2D) phosphorene allotropes, particularly 2D black phosphorene (2D-BlackP) and 2D blue phosphorene (2D-BlueP), are emerging as promising anode materials for next-generation potassium ion batteries (PIBs) due to their high theoretical capacities and favorable electrochemical properties. However, the microscopic interaction mechanisms by which K⁺ ions and phosphorene allotropes alter their electronic structures remain insufficiently understood. In this work, we employ density functional theory (DFT) calculations to systematically investigate the effects of K⁺ adsorption on the valence electronic structures of 2D-BlackP and 2D-BlueP. Molecular orbital analysis reveals that K⁺ adsorption significantly reduces the bandgap of 2D-BlueP, enhancing charge-transfer capability, while exerting only minimal influence on the bandgap of 2D-BlackP. Energetic and charge analyses demonstrate that the extent of ion-induced charge transfer predominantly governs the modulation of the electronic structure, especially under high-pressure conditions where ions approach the basal plane. Furthermore, charge polarization calculations indicate that K+ cations induce a stronger polarization in BlueP than in BlackP, disrupting the intrinsic symmetry of pristine 2D-BlueP and further modulating its electronic characteristics. Diffusion barrier calculations additionally suggest that 2D-BlueP offers favorable ionic transport pathways, underscoring its promise as a high-performance anode material for PIBs. These findings provide molecular-level insights into ion–phosphorene interactions and highlight design principles for exploiting phosphorene allotropes in efficient, fast-charging energy storage systems.