Photoanodes properties

Watanabe A, Kozuka H (2003) Photoanodic properties of sol-gel derived FeBOs thin films containing dispersed gold and silver particles. J Phys Chem 107 12713-12720... 

M. Matsumura and S. R. Morrison, Photoanodic properties of an n-type of silicon electrode in aqueous solutions containing fluorides, J. Electroanal. Chem. 144, 113, 1983. 

Hida, Y., Kozuka, H. Photoanodic properties of sol-gel-derived iron oxide thin films with embedded gold nanoparticles effects of polyvinylpyrrolidone in coating solutions. Thin Solid Films 476, 264 (2005). doi 10.1016/j.tsf.2004.09.063... 

The sol-gel process to prepare SIO2 glass fibers and T102 films has been reviewed. It has been known that the hydrolysis conditions such as molar ratio of water to alkoxide and reaction temperature are critical to the desired forms of the gel product (fiber, film or bulk). Some properties of the resultant products have been examined. Especially, Ti02 films have been attempted to use as a photoanode for decomposition of water, and their photoelectrochemical properties are described in comparison with the results previously obtained for single crystal and polycrystalline TiC>2, and are discussed in terms of the microstructure of the film. 

The use of nanocarbon-semiconductor hybrid materials thus offers a great potential to the design and development of novel/improved photocatalysts and photoanodes, but it is necessary to have a detailed understanding of the many factors which determine the overall properties. This chapter will analyze these aspects presenting a concise analysis of the topic with selected relevant developments in the field, mainly in the last few years. 

The protons/electrons produced in water oxidation at a photoanode side of a PEC device could be used (on the cathode side) to reduce C02 to alcohols/hydrocarbons (CH4, CH30H, HC00H, etc.). In this way, an artificial leaf (photosynthesis) device could be developed [11]. While nanocarbon materials containing iron or other metal particles show interesting properties in this C02 reduction [106], it is beyond the scope of this chapter to discuss this reaction here. It is worthwhile, however, to mention how nanocarbon materials can be critical elements to design both anode and cathode in advanced PEC solar cells. Nanocarbons have also been successfully used for developing photocatalysts active in the reduction of C02 with water [107]. 

There are many different mechanisms through which the nanocarbon-semiconductor hybrid materials may show enhanced properties and which have to be exploited for the design of optimized materials used as photocatalysts or photoanodes. The presence, absence or efficacy of these enhancement mechanisms depends greatly on the... 

Iron oxide (Fe Oj) and tungsten oxide (WO ) films have been studied and developed as candidate semiconductor materials for the PEC junction (photoanode). High-temperature synthesis methods, as reported for some high-performance metal oxides, have been found incompatible with multijunction device fabricatioa A low-temperature reactive sputtering process has been developed instead. In the parameter space investigated so far, the optoelectronic properties of WO3 films were superior to those of Fe Oj films, which showed high recombination of photogenerated carriers (Miller et al., 2004). 

Crystalline Sn02 and WO3 photoanodes for water photoelectrolysis have been reported [24-26], The band gap of Sn02 (Erg = 3.5 eV) makes single crystals of this material of little interest with respect to solar induced optical properties. Wrighton and coworkers observed... 

Nanocrystalline semiconductor thin film photoanodes, commonly comprised of a three dimensional network of inter-connected nanoparticles, are an active area of photoelectrochemistiy research [78-82] demonstrating novel optical and electrical properties compared with that of a bulk, thick or thin film semiconductor [79,80]. In a thin film semiconductor electrode a space charge layer (depletion layer) forms at the semiconductor-electrolyte interface charge carrier separation occurs as a result of the internal electric... 

A few other applications of dithiolenes make use of their redox properties. Kumar et a/.219 proposed the use of dithiolenes as photosensitizers. Umezawa et al.22<> coated a Pt cathode with (Et4N)Ni(mnt)2 and saw a modest degree (1.4 x 10 4 %) of light conversion upon irradiation. On the opposite side, Bradley et al.721 used dithiolenes to stabilize n-type Si anodes against photoanodic decomposition. 

Chl-coated semiconductor (n-type) electrodes and metal electrodes can act as efficient photoanodes and photocathoes, respectively, for visible light conversion. The former system functions as a dye-sensitized semiconductor electrode, while the latter is presumably driven by the photoconductive properties of a Chi solid layer and/or charge separation involving the Chl-metal contact barrier. 

In contriving optimal photosplitting of water, it is desirable to irradiate two photoelectrodes. In considering photoanodes, it is difficult to achieve suitable properties with semiconducting oxides, which tend to be stable under oxygen evolution. On the other hand, arsenides and sulfides appear to have more suitable photoelectrochemical properties, but are clearly unstable when exposed to Oz evolution, (b) What experimental procedures could be used to overcome this difficulty (Bockris)... 

Photoelectrochemical splitting was discussed extensively in Chapter 10. The key point is the use of trace electrocatalysts added to the surface of both photocathode and photoanode to the appropriate extent (Kainthla, Zelenay, and Bockris, 1987 Turner, 1998). If the electrolyzer is to be entirely solar driven, both electrodes must be irradiated. It is difficult to find photoanodes with the appropriate properties. Most of them dissolve electrochemically ifused as anodes for02 evolution. This can, however, be prevented by using transparent films of nonreactive oxides (Bockris and Uosaki, 1977). 

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