Bromide electrosorption on the low-index faces of silver
Abstract
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 KPF6 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 σi of the bromide ions, for σi equal and opposite to the charge density σM on the metal, shows a rather abrupt decrease in slope with a decrease in σi. Moreover, the plots of σivs.σM at constant c intersect for σi≈–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 |σi| on Ag(110). The potential difference across the inner layer, once plotted against |σi| at constant σM, attains a maximum value before shifting linearly towards more negative values with a further increase in |σi|; 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.