Titanium-supported titania photoelectrodes made by sol-gel processes

Titanium-supported titania-based photoelectrodes were prepared either by so l-gel processes or by thermal oxidation. Catalytic activities and stabiliti es of these photoelectrodes were monitored by photooxidizing formic acid in aqueous NaCl during three successive experiments under identical condition s. Although electrodes coated with either titania (higher activity) or zirc onia-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. Stabilit ies of multilayer electrodes were improved by depositing the sol faster. Ap plying positive electrical potentials across electrodes also increased thei r activities. In particular, while activities diminished considerably in re latively high concentrations of NaCl if no potential was present, activitie s decreased only slightly under an electrical field. Activities of photoele ctrodes prepared by heating metallic titanium plates at 300 degrees C were low. Activities of photoelectrodes prepared by heating titanium at 500 degr ees C (giving a rutile coating) were similar to activities of photoelectrod es prepared by sol-gel techniques, but only when potentials were applied.