Low-temperature electrodeposition approach leading to robust mesoscopic anatase TiO2 films.

Anatase TiO2, a wide bandgap semiconductor, likely the most worldwide studied inorganic material for many practical applications, offers unequal characteristics for applications in photocatalysis and sun energy conversion. However, the lack of controllable, cost-effective methods for scalable fabrication of homogeneous thin films of anatase TiO2 at low temperatures (ie. < 100 °C) renders up-to-date deposition processes unsuited to flexible plastic supports or to smart textile fibres, thus limiting these wearable and easy-to-integrate emerging technologies. Here, we present a very versatile template-free method for producing robust mesoporous films of nanocrystalline anatase TiO2 at temperatures of/or below 80 °C. The individual assembly of the mesoscopic particles forming ever-demonstrated high optical quality beads of TiO2 affords, with this simple methodology, efficient light capture and confinement into the photo-anode, which in flexible dye-sensitized solar cell technology translates into a remarkable power conversion efficiency of 7.2% under A.M.1.5G conditions.

Room-temperature synthesis of iron-doped anatase TiO2 for lithium-ion batteries and photocatalysis.

Iron-doped nanocrystalline particles of anatase TiO2 (denoted x% Fe-TiO2, with x the nominal [Fe] atom % in solution) have been successfully synthesized at room temperature by a controlled two-step process. Hydrolysis of titanium isopropoxide is first achieved to precipitate Ti(OH)4 species. A fine control of the pH allows one to maintain (i) soluble iron species and (ii) a sluggish solubility of Ti(OH)4 to promote a dissolution and condensation of titanium clusters incorporating iron, leading to the precipitation of iron-doped anatase TiO2. The pH does then influence both the nature and crystallinity of the final phase. After 2 months of aging at pH = 2, well-dispersed nanocrystalline iron-doped TiO2 particles have been achieved, leading to 5-6 nm particle size and offering a high surface area of ca. 280 m(2)/g. This dissolution/recrystallization process allows the incorporation of a dopant concentration of up to 7.7 atom %; the successful incorporation of iron in the structure is demonstrated by X-ray diffraction, high-resolution transmission electron microscopy, and Mössbauer spectroscopy. This entails optical-band-gap narrowing from 3.05 to 2.30 eV. The pros and cons effects of doping on the electrochemical properties of TiO2 versus lithium are herein discussed. We reveal that doping improves the power rate capability of the electrode but, in turn, deserves the electrolyte stability, leading to early formation of SEI. Finally, we highlight a beneficial effect of low iron introduction into the anatase lattice for photocatalytic applications under standard AM1.5G visible-light illumination.