Estudo das propriedades fotoeletroquímicas e ópticas de filmes finos de hematita aplicados a geração de hidrogênio via hidrólise fotoassistida

Abstract

A very interesting way to use solar energy is by its convertion into chemical energy (fuel), such as the solar H2 production by water splitting. In this work, hematite thin films were prepared by a simple sol gel method and investigated as photoanodes in H2 production by photoassisted hydrolysis. Two systematic studies were performed regarding the effects of the annealing and Sn doping on the material. The photoelectrochemical performance was shown to increase significantly for films deposited on SnO2:F/glass subjected to high temperature (T) annealing (>750 °C). Strong correlation was found between photogenerated current, donor concentration, and Sn concentration as determined by impedance analysis and X-ray photoelectron spectroscopy. On the other hand, the study with doped material showed that Sn acts as impurity donor and also facilitates the oxidation of water on the surface of hematite. The effects of thermal annealing and Sn addition on the optical properties of hematite films were determined by spectroscopic ellipsometry. The band gap energy was found to be 2.21 eV and independent of microstructure and of Sn concentration for all studied films. However, it was shown that important information regarding the dielectric function of hematite films can help to understand their photoelectrochemical performance.