Applications of Electrochemically Deposited Sol-Gel Films

The most common sol—gel system that has been electrochemically deposited is based on silane, although electrochemical deposition of non-silicon sol-gel films from metal alkoxides has also been reported [3-6]. Early studies mainly dealt with the electrochemical deposition behavior of different silanes and their mixtures. The silanes include tetramethoxysilane (TMOS), tetraethoxysilane (TEOS), and organofunctional silanes such as 3-aminopropyltriethoxysilane (APTES) and 3-mercaptopropyltrimethoxysilane (MPTMS). The electrochemically deposited silane films find applications in electroanalysis, corrosion... 

The electrochemical deposition approach is versatile and applicable to various sol-gel systems, including silanes and metal alkoxides. Most of the research has focused on the electrodeposition of silane-based sol-gel films. The latter are typically electrodeposited from aqueous solutions of the monomers in the presence of ethanol or methanol as a cosolvent The deposition is usually carried out at cathodic potentials, although a few groups [11,14,15] also reported the anodic electrodeposition process. Electrodeposition of non-silicon sol-gel films from... 

Most film and particle formation techniques can be divided into gas-phase and liquid-phase deposition processes, which are briefly discussed in this section. Deposition of metal and metal oxides from metal enolate sources results from application of CVD, ALD, spin-coating, electrochemical and sol-gel methods, which are discussed in detail... 

The main driving force for the electrochemical deposition of sol—gel films is the electrolysis of H2O, which not only generates OH ions but also induces H2 evolution on the cathode. The latter causes the deposited films to be porous. This structure may deteriorate the corrosion resistance of the films as reported by Hu et al. [18,42], but on the other hand it is beneficial for the application of the films in electroanalysis, as it does not completely block electron transfer on the electrode [20,28]. The pores induced by H2 are large, and the obtained films are macroporous consisting of silica particles with diameter of a few himdred nanometers. In order to better tune the morphology of the films, templates are desired for electrodeposition. 

Sol-gel materials are also known as an excellent matrix for embedding other species due to their tunable physical properties (e.g., flexibility and transparency), high chemical stability, and mild operating conditions. Especially, electrochemical deposition of silane-based sol-gel Aims is usually carried out under mild acidic aqueous solutions at pH 3-6. This allows the co-electrodeposition of silane with nanoparticles [47-50], carbon nanotubes [51-53], metals [54-57], polymers [50,58], enzymes [52,53,59-65], bacteria [66,67], and more. Thus, most of the recent research worlcs also focus on the electrochemical deposition of sol-gel-based composite Aims, with the concern of improving the films performance in corrosion protection, electroanalysis, microextraction, and so on and further broadening the films applications. 

The electrochemical deposition approach was initially used for depositing orga-nofunctional silane sol-gel films for promoting adhesion between aluminum alloy and epoxy resin [Ij. Later, it was used for preparing silane films for corrosion protection of metals, electrochemical stripping analysis of metal ions, and microextraction of organic compounds [18,20,22,42,45]. The recent development of the electrochemical deposition of sol-gel-based composite films opens various applications such as encapsulating proteins, enzymes, and bacteria. In this section, we will show three main applications of eiectrodeposited sol-gel films, that is, corrosion protection and adhesion promotion, electrochemical sensors, and finally biocomposite films. Other applications such as solid-phase microextraction (SPME), nonlinear optics, antireflection, electrocatalysis, and superhydrophobic films are also discussed. 

This chapter is intended to cover major aspects of the deposition of metals and metal oxides and the growth of nanosized materials from metal enolate precursors. Included are most types of materials which have been deposited by gas-phase processes, such as chemical vapor deposition (CVD) and atomic layer deposition(ALD), or liquid-phase processes, such as spin-coating, electrochemical deposition and sol-gel techniques. Mononuclear main group, transition metal and rare earth metal complexes with diverse /3-diketonate or /3-ketoiminate ligands were used mainly as metal enolate precursors. The controlled decomposition of these compounds lead to a high variety of metal and metal oxide materials such as dense or porous thin films and nanoparticles. Based on special properties (reactivity, transparency, conductivity, magnetism etc.) a large number of applications are mentioned and discussed. Where appropriate, similarities and difference in file decomposition mechanism that are common for certain precursors will be pointed out. 

Thin films and coatings can be fabricated by vapor deposition [i.e., chemical vapor deposition (CVD) and electrochemical vapor deposition (EVD)], sputtering, sol-gel processing, and electrophoretic depositionElectrochemical vapor deposition, a thin-film technique, is used to form thin ( 40 pm) layers of dense yttria-stabilized zirconia in the seal-less tubular solid oxide fuel celP ". Thin layers of stabilized zirconia are required in this application to keep the internal resistance and the operating temperature of the electrochemical device as low as possible. 

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