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) KPF6 solutions over a range of c from 1x10(-6) to 5x10(-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 sigma(i) of the bromide ions, for sigma(i) equal and opposite to the charge density sigma(M) on the metal, shows a rather abrupt decrease in slope with a decrease in sigma(i). Moreover, the plots of sigma(i) vs. sigma(M) at constant c intersect for sigma(i)-35 mu C 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 /sigma(i)/ on Ag(110). The potential difference across the inner layer, once plotted against /sigma(i)/ at constant sigma(M), attains a maximum value before shifting linearly towards more negative values with a further increase in /sigma(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.