Admittance studies of the EQCM on rough surfaces. The double layer region

The admittance of the electrochemical quartz crystal microbalance (EQCM) was studied for gold surfaces of different morphologies, produced by electrodeposition of gold at current densities near the limiting current density. It was observed that at surfaces of certain morphology, the real and the imaginary parts of the EQCM response become very sensitive to changes of potential in the double-layer region, even when Faradaic reactions and specific adsorption do not take place. This effect masks smaller effects of mass and viscosity changes in the diffuse double layer, described in our previous publication. It was suggested that this rather large effect is a result of surface hydration, depending on electrode potential. Orientation of water molecules in the first layer attached to the surface results in a shift of the equilibrium between clusters of water of different sizes in the “transition” layer. The latter determines the viscosity of this layer.