Electrochemically Assisted Deposition of Nanoporous Silica Membranes on Gold Electrodes: Effect of 3‐Mercaptopropyl(trimethoxysilane) “Molecular Glue” on Film Formation, Permeability and Metal Underpotential Deposition

Abstract

AbstractGold electrodes have been covered with vertically aligned mesoporous silica thin films by electro‐assisted self‐assembly. To ensure uniform surface coverage and good adhesion of the membrane to the gold surface, it was necessary to use a (3‐mercaptopropyl)trimethoxysilane (MPTMS) reagent to act as a “molecular glue” thanks to its thiol functionality, which is able to bind to the gold substrate and to its alkoxysilane moieties enabling condensation with the silica material. The MPTMS layer had, however, a significant effect on film permeability to redox species [Ru(NH3)63+ and ferrocenedimethanol (Fc(MeOH)2)]. MPTMS adsorption should be long enough to ensure proper adhesion of the film but not too long so as to avoid surface blocking or film defects; an optimal time window of 60–600 s soaking in 0.1 mM MPTMS in ethanol was evidenced. In addition, Cu underpotential deposition (UPD) experiments revealed that the silica membrane significantly affected the UPD process, suggesting some barrier effect of the porous membrane, but the interface Au/MPTMS/silica is not sharp and allowed metal UPD between the gold substrate and the silica thin film.