Influence of Wettability on the Impedance of Ion Transport Through Mesoporous Silica Films

Functionalized nanopores have attracted strong interest in different fields in which nanopore transport is essential. Detailed insights into mass transport through nanopores and its correlation to pore wall properties such as wettability are essential. The potential and challenges using electrochemical impedance spectroscopy (EIS) to analyze mass transport through mesoporous silica thin films with precisely adjusted wettability are discussed. The accessible area of the electrode, the charge transfer or film resistance and the diffusion coefficients of the redox probe [Ru(NH3)6]2+/3+ inside the mesopores are determined. The influence of experimental parameters such as silica film pre‐treatment is evaluated. Hydrophilic mesoporous films display comparable diffusion coefficients around 1*10–8 cm2 s–1 independently of the exact wettability. As expected, hydrophobic films do not exhibit transport due to water exclusion. The sample pre‐treatment strongly influences the transport characteristics. Incubation into aqueous KCl leads to a decrease in the resistance for all tested mesoporous films. This is ascribed to an increase in the silanol group concentration at the pore wall. Besides the insights into mass transport in mesoporous films and on how to measure EIS in such films, this study elucidates the importance of sample pre‐treatment and surface chemistry concerning mesoporous film performance.