Effect of surface Fe- and Cu-species on the flat-band potential and photoelectrocatalytic properties of N-doped TiO2

Abstract

Surface modification of N-doped TiO₂ photocatalyst with transition metals is regarded as a promising approach to increase its ability in the visible-light driven oxidation of organic compounds. Photoelectrocatalytic characterization of semiconducting materials is useful technique to evaluate the potentials of photogenerated charge carriers for analysis of their transfer and reaction pathways. In this study, the surface of TiO₂-N was decorated with iron or copper species by a simple impregnation method. Fe and Cu were selected as efficient surface traps for electrons and holes, respectively. The metal-decorated photocatalysts were studied using a series of (photo)electrochemical methods with/without addition of methanol as a sacrificial agent to evaluate the position of their flat-band potentials and investigate the effect of metals on the action spectrum of TiO₂-N in the range of 370–500 nm. Comprehensive analysis revealed that the flat-band potentials of Fe- and Cu-modified photocatalysts are similar (−0.30 ÷ −0.32 V vs. RHE) and slightly negative than the potential of initial TiO₂-N (−0.26 V vs. RHE). Furthermore, the modification of TiO₂-N with iron and copper species substantially increased visible-light induced photocurrent in both aqueous and methanol-added electrolytes, especially at long wavelengths. The enhanced photoelectrocatalytic activity of metal-decorated photocatalysts was considered in viewpoint of metal effect on the recombination of photogenerated charge carriers and occurring water or methanol oxidation reactions.