Metal oxides photoanodes properties

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). 

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]. 

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