Optimization of Titania Post-Necking Treatment of TaON Photoanodes to Enhance Water-Oxidation Activity under Visible-Light Irradiation

A post-necking treatment of porous screen-printed TaON films with titania is optimized to improve their photocatalytic activity for water oxidation under visible-light irradiation (lambda > 400 nm). Post-necking was achieved by applying TiCl4 solutions in ethanol or water, or Ti(iOPr)(2)(acac)(2) (acac=acetylacetonate) in isopropanol to the films, followed by calcination at 450 degrees C in air. Under voltammetric and chronoamperometric conditions in Na2SO4 (0.1m, pH 6), a 25-fold enhancement in oxidative photocurrent densities is achieved upon post-necking of TaON by using ethanolic TiCl4, whereas aqueous TiCl4 and Ti(iOPr)(2)(acac)(2) precursors afforded improvements of eight-and sixfold, respectively. SEM and electrochemical impedance spectroscopy studies confirm that post-necking improves the interconnectivity of the particles and facilitates charge transfer within the photoanode and at the electrode-electrolyte interface. The highest improvement in activity was achieved by using ethanolic TiCl4 to deposit 10-20 wt% TiO2 on the TaON films, whereas higher loadings deteriorated the performance.