Work Function Signatures of Oxide and Sulfide Formation on Cu–Ni Alloy Surfaces

Kohn–Sham density functional theory (DFT) modeling was employed to interpret atomistic mechanisms that govern work function evolution in binary copper–nickel alloys that are aged under typical marine environmental exposure conditions. Simulations revealed that initial Cu2O formation and Ni enrichment from selective Cu dissolution increased the work function, but subsequent copper and oxygen vacancy generation within the oxide and hydroxylation at the outer surface drove its decrease at longer times. These predictions were confirmed experimentally using ex situ scanning Kelvin probe measurements of samples aged in quiescent and agitated artificial seawater (ASW) for up to 504 h, and these samples exhibited the same rise–fall trend in work function. DFT models further indicated that sulfide contamination leading to the formation of Cu2S increased the work function. Coupled with enhanced Cu oxidation, Cu2S formation suggested spatial heterogeneity in the work function following sulfide exposure. Consistent with these predictions, Kelvin probe mapping showed nonuniform distributions in the work function when Na2S was introduced prior to aging. By integrating predictive DFT modeling with experimental validation, this work establishes a mechanistic framework for interpreting alloy surface evolution in marine environments and highlights the critical role of defects and contaminant interactions in governing electronic properties.