Bromide electrosorption on the low-index faces of silver

Bromide adsorption on the three low-index faces of silver was investigated from mixed c mol dm -3 KBr + (0.02 - c) mol dm -3 KPF 6 solutions over a range of c from 1 × 10 -6 to 5 × 10 -3 mol dm -3 using the potential-step chronocoulometric technique. The adsorption behaviour on the Ag(110) face shows significant differences with respect to that on the Ag(111) and Ag(100) faces. Thus, the plot of the applied potential E vs. the specifically adsorbed charge density σ i of the bromide ions, for σ i equal and opposite to the charge density σ M on the metal, shows a rather abrupt decrease in slope with a decrease in σ i. Moreover, the plots of σ i vs. σ M at constant c intersect for σ i ≈ -35 μC cm -2. This behaviour is explained by a decrease in the negative value of the surface potential due to electron smoothing with an increase in |σ i| on Ag(110). The potential difference across the inner layer, once plotted against |σ i| at constant σ M, attains a maximum value before shifting linearly towards more negative values with a further increase in |σ i|; this behaviour, observed on all three low-index faces, is interpreted on the basis of a molecular model of the inner layer which accounts for the reorientation of the water dipoles and for the screening by the inhomogeneous electron gas.