Abstract
Anodic oxidation of metals leads to the formation of ordered nanoporous or nanotubular oxide layers that contribute to numerous existing and emerging applications. However, there are still numerous fundamental aspects of anodizing that have to be well understood and require deeper understanding. Anodization of metals is accompanied by the inevitable phenomenon of anion incorporation, which is discussed in detail in this review. Additionally, the influence of anion incorporation into anodic alumina and its impact on various properties is elaborated. The literature reports on the impact of the incorporated electrolyte anions on photoluminescence, galvanoluminescence and refractive index of anodic alumina are analyzed. Additionally, the influence of the type and amount of the incorporated anions on the chemical properties of anodic alumina, based on the literature data, was also shown to be important. The role of fluoride anions in d-electronic metal anodizing is shown to be important in the formation of nanostructured morphology. Additionally, the impact of incorporated anionic species, such as ruthenites, and their influence on anodic oxides formation, such as titania, reveals how the phenomenon of anion incorporation can be beneficial.
Highlights
Anodization is a commonly used name for electrochemical oxidation of metals [1,2,3], their alloys [4,5] and semiconductors [6,7,8] under either galvanostatic or potentiostatic conditions in a two-electrode setup since the oxidized material plays a role of an anode
Anion incorporation during anodizing of metals plays an important role in the formation of anodic oxides, influencing the resulting morphology
The models of anion incorporation in anodic alumina and titania were discussed in detail
Summary
Anodization is a commonly used name for electrochemical oxidation of metals [1,2,3], their alloys [4,5] and semiconductors [6,7,8] under either galvanostatic or potentiostatic conditions in a two-electrode setup since the oxidized material plays a role of an anode. The incorporation of electrolyte anions into the nanostructured anodic oxides is of particular interest, Molecules 2021, 26, 6378 as it can influence multiple properties of the formed material, and provide interesting applications. In this short literature review, the most relevant and interesting findings on anion incorporation during anodization of selected metals are showcased and discussed in detail. The most important question we want to answer in this review is which properties, and to what extent, can be modified by the electrochemical doping of anodic oxides with anionic electrolyte species, and hopefully inspire further progress in this field
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