Photoelectrochemical properties of sol-gel and particulate TiO2 layers

Polarization curves on irradiated TiO2 layers were measured in various electrolytes, namely sodium hydroxide, sulphuric acid, oxalic acid and potassium oxalate. Photocurrents measured in 0.1 M NaOH are very small and decrease with increasing number of Degussa P25 TiO2 layers. Photocurrents for sol-gel TiO2 layers in 0.1M NaOH are about five times higher than for P25 TiO2 layers and increasing with number of layers. The same holds for Na2SO4, but in H2SO4 the difference between P25 and sol-gel diminishes, however the sol-gel layers still show the higher currents. In solutions of oxidizable substrates the trend is inversed: P25 layers show higher currents, with a steep increase with concentration of solute. The shape of the polarization curves was interpreted in terms of response time to irradiation and photocurrent depletion. Degradation experiments demonstrated that the effect (and advantage) of biasing the electrode depends on adsorption properties of substance and surface area of electrode material.