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Chapitre D'ouvrage Année : 2006

Modified titanium electrodes

Résumé

Titanium is a valve metal that is reported to be corrosion-resistant in acid media ; that property is attributed to the formation of a passive TiO2 film at the surface of the metal. The chemical stability and the electrochemical properties of TiO2 layers are strongly dependent on their preparation process. A careful study of those properties is a necessary step to propose titanium as a substrate for anodes in industrial electrolytic cells. Deposition of an electronic conductor coating on Ti/TiO2 substrates leads to « modified titanium electrodes ». These deposits may be: a noble metal (platinum) or a metallic oxide (RuO2, IrO2, PbO2...), i.e. conducting compounds which exhibit an electrocatalytic behaviour vs specific electrochemical reactions. In the present chapter, a particular attention is given to the electrochemical behaviour of modified titanium electrodes in aqueous solutions. First, the properties of the substrate are recalled. The passive layer is composed of TiO2, a n-type semiconductor that may be formed by thermal oxidation, chemical oxidation, or anodisation. The composition, thickness and electrochemical properties of those films are reviewed. Their conductivity may be enhanced considerably by doping. Second, the modification of the substrates by cathodic electrodeposition of a metal is described. That procedure is useful for preparing anodes coated with a noble metal. For example, Ti/TiO2/Pt structures exhibit a very interesting reactivity that will be illustrated by cyclic voltammetry or impedance spectroscopy experiments. Third, the modification of titanium electrodes by a metallic oxide is reviewed. It leads to the preparation of the well-known Dimensionally Stable Anodes (DSA). Their chemical mode of preparation is given, as well as the mechanisms involved in the use of these anodes and their deactivation process. It is also possible to deposit metallic oxides by an anodic process. The present paper is focussed on PbO2 electrodeposition, leading to « low-cost DSA » that may be used for the oxidation of Cr(III) to Cr(VI) in sulphuric acid. The anodic electrodeposition of PbO2 on oxidised polycrystalline Ti electrodes has been observed locally in particular circumstances; it occurs selectively on the (0001) grains. The topics reviewed in this paper are described using a large amount of data that were obtained in our laboratory.
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Dates et versions

hal-00076834 , version 1 (28-05-2006)

Identifiants

  • HAL Id : hal-00076834 , version 1

Citer

Didier Devilliers, Eric Mahé. Modified titanium electrodes. Magdalena Nunez. Trends in Electrochemistry Research, Nova Science Publishers Inc., New York, USA, pp.1, 2006, ISBN: 1-59454-457-3. ⟨hal-00076834⟩
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