Electrochemical comparative study of titania (anatase, brookite and rutile) nanoparticles synthesized in aqueous medium

Titanium oxide TiO₂ has found extensive use in a great variety of applications among which electrode materials for dye-sensitized solar cells. The polymorphs of TiO₂, rutile, anatase and brookite exhibit specific physical properties, band gap, electronic surface states. For many applications the size of particles was an important parameter because it determines the surface to volume ratio, which greatly influences many properties. TiO₂ anatase was the most used phase for photovoltaic applications and brookite seems potentially interesting. Nanometric particles of the three polymorphs were synthesized in aqueous medium in order to compare the electronic properties of these materials for photovoltaic devices. No significant difference was observed between the phases by cyclic voltammetry. The surface and consequently the electrode preparation seemed to be the main parameter. The measurement of double layer capacitance has shown the film activation initially insulating and strong frequency dependence. After dye sensitization, it has been observed that at low I₂ concentration in solution (with a fixed concentration of I^-), the open circuit voltage (V_oc) was independent of this concentration while above a certain threshold for I₂, V_oc decreased logarithmically with the iodine concentration.