Photoresponse and donor concentration of plasma-sprayed TiO₂ and TiO₂-ZnO electrodes

The photoelectrochemical characteristics of plasma-sprayed porous TiO₂, TiO₂-5%ZnO, and TiO₂-10%ZnO electrodes in 0.1 N NaOH solution were studied through a three-electrode cell system. The microstructure, morphology, and composition of the electrodes were analyzed using an electron probe surface roughness analyzer (ERA-8800FE), scanning electron microscopy, and x-ray diffraction. The results indicate that the sprayed electrodes have a porous microstructure, which is affected by the plasma spray parameters and composition of the powders. The TiO₂-ZnO electrodes consist of anatase TiO₂, rutile TiO₂, and Zn₂Ti₃O₈ phase. The photoresponse characteristics of the plasma-sprayed electrodes are comparable to those of single-crystal TiO₂, but the breakdown voltage is close to 0.5 V (versus that of a saturated calomel electrode). The short-circuit photocurrent density (J_SC) increases with a decrease of donor concentration, which was calculated according to the Gartner-Butler model. For the lowest donor concentration of a TiO₂-5%ZnO electrode sprayed under an are current of 600 A, the short-circuit J_SC is approximately 0.4 mA/cm² higher than that of the TiO₂ electrodes under 30 mW/cm² xenon light irradiation. The J_SC increases linearly with fight intensity.