Preparation of Metal Oxide Electrodes by Electrodeposition

Three-dimensionally nanostructured transparent conducting ZnO could serve as electrode for several applications such as dye-sensitized solar cells. Thus, the template-assisted nanopatterning of ZnO via electrodeposition was attempted, following the 

the template-assisted nanostructured deposition of NiO was tried, following the experimental method of Sonavane et al. for the electrodeposition of nontemplated coatings [62]. For this purpose a 0.5M aqueous NiCl bath containing 0.1 M KCl was prepared, which was complexed using EDTA and pH-adjusted to 8 by addition of KOH. Electrodeposition was conducted in a three-electrode cell at a potential of -1.1 V versus Ag/AgCl for lOOmin. The obtained DG-structure NiO film of about 1 ttm thickness is presented in Fig. 5.5. This preparation technique has two major disadvantages firstly, the very slow deposition rate, and secondly, the transparency of the deposit complicates the anyway difficult preparation route. In Chap. 6, a more elegant approach for nanostructured NiO deposition is presented that overcomes these issues. 

The open circuit potential of fully porous double-gyroid templates on FTO when immersed in electrolyte was 480 10 mV. A deposition rate of approximately 9.2 nm s was observed for the replication of gyroid templates. The deposited film thickness was measured by SEM imaging of prepared cross-sections. The typical current variation during deposition is shown in Fig. 5.7c. Similarly, nontemplated and inverse opals (lO) were prepared under the same conditions, except that the required deposition time for the same deposition thickness was much shorter. The deposition rate in colloidal arrays made from poly(styrene) mlcrospheres with a diameter of 400 nm, was approximately 60nms .  

Using SU-8 patterned FTO substrates to create visible design patterns and small area electrodes worked exceptionally well, see Fig. 5.3 [63]. Additionally, limiting the deposition area with a SU-8 mask allowed an improved control over the tern-plated electrodeposition yielding defect-free deposits of homogeneous thickness, see Fig.5.12. 

Directly after deposition the films were rinsed and immersed into DI water for several minutes. Failing to do so or using ethanol instead of water resulted in nonporous V2O5 free-surfaces as depicted in Fig. 5.8. In order to improve the crystallinity of 

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