Polycrystalline Photoanode Materials

Polycrystalline oxide materials, both undoped and doped, have been extensively examined for use as photoanodes. Ti02 electrodes have been prepared by thermal oxidation of a Ti plate in an electric furnace in air at 300-800°C (15-60 min) and in a flame at 1300°C (20 min) [27-30]. XRD analysis of thermally oxidized samples indicates the formation of metallic sub-oxide interstitial compounds, i.e. TiOo+x (x 0.33) or Ti20i y (0 y 0.33) and Ti30 together with rutile Ti02 [27]. The characteristic reflection of metallic titanium decreases in intensity after prolonged oxidation (60 min) at 800° C indicating the presence of a fairly thick oxide layer (10-15 pm). Oxidation at 900°C leads to poor adhesion of the oxide film 

The use of polycrystalline La doped SrTiOs as a photoanode has also been investigated [31]. La is considered an appropriate dopant because of its stability in trivalent state and the similarity of the ionic radii for Sr (1.40 A) and La (1.32 A), which ensures its incorporation at Sr sites. Doping leads to the formation of a new energetic deep donor sub-level (Ti sd) in the band gap, thereby shifting its response towards the visible region. Similarly doping of polyciystalline Ti02 has shown an increase 

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