Correlation between photoelectrochemical behaviour and photoelectrocatalytic activity and scaling-up of P25-TiO2 electrodes

The use of TiO2 electrodes may solve the two main drawbacks of photocatalytic processes: i) the necessity of recovering the catalyst and ii) the low quantum yield in the use of the radiation. This work focuses on the correlation between the photoelectrochemical properties of TiO2 electrodes and their activity for the photoelectrocatalytic oxidation of methanol. Particulate TiO2 electrodes prepared by deposition of P25-TiO2 nanoparticles on titanium (TiO2/Ti) or conductive glass support (TiO2/ITO) seem to be effective for charge carrier transference on TiO2 surface favouring the formation of OH radicals and consequently, the oxidation of molecules. In contrast, thermal TiO2 electrodes prepared by annealing of titanium (Ti) present better properties for charge carrier separation as a consequence of the application of a potential bias. Despite reducing charge carrier recombination by applying an electric potential bias, the activity of thermal electrodes remains lower than that of P25-particulate electrodes. TiO2 structure of P25-particulate electrodes does not completely allow developing a potential gradient. However, their adequate TiO2 layer characteristics for charge carrier transfer lead to a reduction in charge carrier recombination making up for the lack of charge carrier separation when applying an electric potential bias. TiO2/Ti showed the highest values of activity. Therefore, the combination of the suitable TiO2 surface properties for charge carrier transfer with an adequate conductive support seems to increase the properties of the electrode for allowing charge carrier separation. The scaling-up calculations for a TiO2/ITO electrode do lead to good estimations of the activity and photocurrent of larger electrodes since this photoanode made from ITO as conductive support does not seem to be significantly affected by the applied potential bias.