Selenium-doped WS₂ for improved humid-air lubricity via weakened interfacial hydrogen bonding

The degradation of the tribological performance of WS₂ in humid environments represents a persistent scientific and practical challenge, limiting its application scope despite its excellent lubricity in inert atmospheres. While the superior moisture tolerance of WSe₂ has been recognized, the fundamental atomic-scale mechanisms governing this difference remain inadequately understood. This work addresses this critical knowledge gap by revealing that this disparity originates from the distinct hydrogen bond strengths formed at the material–water interface. Through integrated density functional theory (DFT) calculations and experimental validation, we quantitatively demonstrate that water molecules form significantly weaker O–H···Se hydrogen bonds with WSe₂ (bond lengths: 3.02–3.25 Å) compared to O–H···S bonds with WS₂ (2.80–2.98 Å). This fundamental difference manifests functionally as a 35% lower interlayer sliding energy barrier for WSe₂ under humid conditions, providing the first atomistic explanation for its sustained lubricity. Leveraging this mechanistic insight, we propose and validate a novel materials design strategy: selectively doping the WS₂ lattice with selenium to engineer its interfacial chemistry. The developed W–S–Se coating exhibits remarkable performance, achieving an 18% reduction in the coefficient of friction and a 78% decrease in the wear rate at 40% RH compared to pristine WS₂. Extensive characterization confirms the formation of a reoriented, crystalline transfer layer with insignificant oxidation. This study establishes a new paradigm for solid lubricant design, shifting the focus from conventional microstructure optimization toward direct atomic-level engineering of interfacial water interactions, opening avenues for developing advanced lubricants operable across diverse environmental conditions.