Sol-Gel Coatings by Electrochemical Deposition

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 Sol-Gel Handbo Syndesis, Characterization, and Applications, First Edition. 

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 

The sol-gel system is dynamic where the sol undergoes hydrolysis and condensation to form a gel. Therefore, the sol-gel process is determined by the kinetics of the hydrolysis and condensation reactions. A clear stable sol solution consists of hydrolyzed monomers with low condensation rate, while the gelifica-tion process requires condensation of monomers. The hydrolysis and condensation reactions for alkoxysilanes are depicted as follows [7,16]  

The electrochemical deposition of sol-gel films provides an alternative for shifting the pH on the substrate. In aerated aqueous media, it is well known that by applying cathodic potential, the following reactions occur at the electrode surfece [16,18]  

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Dense electrolytes with a thickness of 3 pm have been deposited on warm-pressed anode substrates by a graded multi-layer sol-gel coating method. By applying a LSCF cathode, current density of about 840 mA/cm and power density of 588 mW/cm has been realized. It could be demonstrated that it is possible to produce highly dense YSZ electrolyte for SOFC application via sol-gel route. Enhanced electrochemical performances of single cells are expected in the future work through optimizations of fabrication procedures. 

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. 

Several methods for the incorporation of catalysts into microreactors exist, which differ in the phase-contacting principle. The easiest way is to fill in the catalyst and create a packed-bed microreactor. If catalytic bed or catalytic wall microreactors are used, several techniques for catalyst deposition are possible. These techniques are divided into the following parts. For catalysts based on oxide supports, pretreatment of the substrate by anodic or thermal oxidation [93, 94] and chemical treatment is necessary. Subsequently, coating methods based on a Uquid phase such as a suspension, sol-gel [95], hybrid techniques between suspension and sol-gel [96], impregnation and electrochemical deposition methods can be used for catalyst deposition [97], in addition to chemical or physical vapor deposition [98] and flame spray deposition techniques [99]. A further method is the synthesis of zeoUtes on microstructures [100, 101]. Catalysts based on a carbon support can be deposited either on ceramic or on metallic surfaces, whereas carbon supports on metals have been little investigated so far [102]. 

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