Conformal deposition of mesoporous silica thin films on high aspect ratio 3d structured nanomesh electrodes by electrochemically assisted self-assembly

Abstract

This work demonstrates for the first time, a reliable, electrochemically controlled, conformal deposition of high-quality templated mesoporous silica onto large surface area metal nanomesh electrodes. Nanomesh electrodes developed in our group are made up of a rationally designed, multitude of interconnected horizontal and vertical nanowires. The nanowires have a diameter of ∼50 nm with an inter-nanowire spacing of around 50 nm, resulting in billions of nanowires per cm2 footprint area. We show that the extent of silica deposition over these nanomesh electrodes can be electrochemically controlled from conformal coatings (around 8–13 nm thick) uniformly coating the entire nanomesh architecture to complete fill and even overfill of the nanomesh electrodes. Furthermore, quality deposits, free of pinholes and cracks throughout the nanomesh scaffold were obtained, as confirmed by a ruthenium hexamine redox probe and Kr gas adsorption measurement, which is quite surprising especially considering the large internal area of the nanomesh. Finally, we demonstrate that the coated nanomesh electrode effectively trapped the [Ru(NH3)6]3+/2+ species within the silica mesopores, mostly owing to the intricate nano-structuring of the nanomesh electrode. The silica-coated nanomesh electrode showed a 42× enhancement in the trapped redox probe charge compared to planar silica layers, partially reflecting the area enhancement offered by the nanomesh electrode, demonstrating the advantage of the functional coating for electrochemical analysis. We believe that such novel electrode architectures can form the basis for the next generation of functional electrodes applied to sensing and catalysis applications. Graphical abstract We present a reliable electrochemical process for depositing mesoporous silica thin films over high surface area nanomesh electrodes. Excellent control over film thickness is demonstrated along the entire nanomesh structure ranging from conformal thin films, 8–13 nm, to complete fill of the nanomesh. Entrapment of redox probes within the mesopores of the silica film enhances the electrochemical response, an effect crucial for electrochemical sensors.