Bromide adsorption on silver in alkaline solution: A surface analytical study

The electrochemical double layer on Ag in alkaline NaBr solutions was investigated ex situ with x‐ray photo‐electron spectroscopy (XPS). The specimen were removed from the electrolyte with hydrophobic surfaces and under potential control. Potential dependent surface concentrations of the adsorbed anions, cations and the surface excess charge, as well as the amount of adsorbed water were determined. The results obtained for the double layer on Ag in 1 M NaOH+0.1 M NaBr and 1 M NaOH+10−3 M NaBr were compared with alkaline chloride solutions and pure 1 M NaOH. We found evidence for a specific adsorption of hydroxide ions in the basic electrolyte; i.e. the OH−‐surface concentration has to be considered for a proper determination of the cat‐ionic excess charge and the potential of zero charge. Compared to the alkaline chloride solution and pure NaOH, however, an underpotential Ag‐oxide formation below the Nernst‐potential of oxide formation was not observed for the alkaline NaBr solutions, i.e. adsorbed Br− ions inhibit the electrochemical Ag(I) oxide formation.