Monitoring surface ion mobility on aluminum oxide: Effect of chemical pretreatments

Despite of its crucial role in many electrochemical processes, a clear surface chemistry-correlated understanding of interfacial ion mobility is missing. This study presents an improved application of a previously introduced method making use of the scanning Kelvin probe (SKP) technique on aluminum oxide surfaces. The local work function changes, induced by the displacement of the mobile surface ions in an electric field applied across the surface, are monitored as a function of surface chemistry modified by different surface pretreatments and ambient atmosphere. Complementary quartz crystal microbalance (QCM) and surface current measurements reveal how the modified surface chemistry affects the thickness of the adsorbed water layer and the surface conductivity, respectively. Besides the usefulness of the SKP technique for mobility studies, we demonstrate a selective control of the superficial ion mobility by engineering the surface fixed charges.