Titanium-supported titania photoelectrodes made by sol-gel processes

Titanium-supported titania-based photoelectrodes were prepared either by sol-gel processes or by thermal oxidation. Catalytic activities and stabilities of these photoelectrodes were monitored by photooxidizing formic acid in aqueous NaCl during three successive experiments under identical conditions. Although electrodes coated with either titania (higher activity) or zirconia-titania (lower activity) and heated at 300 degrees C were less active initially than similar electrodes heated to higher temperatures, electrodes heated at 300 degrees C were more stable. Activities of titania electrodes were increased by depositing the titania at a higher withdrawal speed (21.5 versus 1.5 cm min(-1)) and by depositing more layers of titania. Stabilities of multilayer electrodes were improved by depositing the sol faster. Applying positive electrical potentials across electrodes also increased their activities. In particular, while activities diminished considerably in relatively high concentrations of NaCl if no potential was present, activities decreased only slightly under an electrical field. Activities of photoelectrodes prepared by heating metallic titanium plates at 300 degrees C were low. Activities of photoelectrodes prepared by heating titanium at 500 degrees C (giving a rutile coating) were similar to activities of photoelectrodes prepared by sol-gel techniques, but only when potentials were applied.