Weighing ions in solution with the quartz crystal microbalance

The response of the electrochemical quartz crystal microbalance was studied on gold electrodes, in the double-layer region, in 0.1 M KOH and CsOH. A shift of frequency of 5-6 Hz is observed, which is equivalent to about two layers of oxide. The change of frequency is attributed to the weight of ions in the diffuse-double layer and to an increase of viscosity in the same region. It is shown that data obtained by this technique cannot be analyzed properly in the submonolayer region, unless the effect of the ions and the high field in the diifuse-double layer are taken into account.