The underpotential deposition that should not be: Cu(1 × 1) on Au(111)

Underpotential deposition of copper on Au(111) is analyzed in the light of first-principles calculations. The existence of a 1 × 1 Cu monolayer on Au(111) at underpotentials can be only understood taking into account the free energy excess delivered by the adsorption of sulfate anions. While a naked copper pseudomorphic monolayer results thermodynamically less stable than bulk copper, accounting for the interaction with sulfate ions delivers an underpotential shift which is comparable with the experimental value.

► Underpotential deposition of copper on Au(111) is analyzed in the light of first-principles calculations. ► The effect of adsorbed sulfate anions on this phenomenon is studied. ► It is concluded that coadsorption of SO4= anions may explain by itself the stability of the Cu 1 × 1 monolayer on Au(111).