Doping of photoactive TiO2 films by DC plasma electrolytic oxidation: Effect of transition metals.

Several beneficial features maintain TiO 2 in the top list of viable materials for photocatalytic purposes. However, its relatively large band-gap (3.0–3.2 eV) still hampers practical applications under sunlight. This work explores Direct Current (DC) Plasma Electrolytic Oxidation (PEO) of titanium as a fast, easily-scalable and single-step tool to synthesise doped TiO 2 photoanodes with controlled morphology, crystalline structure and thickness. Zn-, Cu- and Fe-doped crystalline TiO 2 films were obtained in H 2 SO 4 aqueous solutions containing ZnSO 4 , CuSO 4 and FeSO 4 precursors, respectively. As-prepared TiO 2 films showed a porous and homogeneous sponge-like surface morphology, typical of PEO-produced oxides, and a crystalline phase structure consisting of a mixture of anatase and rutile phases. The anatase content varied in the 54–100 % range and correspondingly the band-gap energy was in the 2.85–3.07 eV range. Doped oxides prepared with a low concentration of the metal precursors showed monochromatic incident-photon-to-current-efficiency (IPCE) values exceeding those obtained with pristine TiO 2 by up to 24 %, best performing in the order Zn- > Cu- > Fe-doped TiO 2. Photocurrent under polychromatic UV-Vis irradiation showed an analogous trend and the estimated efficiency of solar-light harvesting was in the 0.3–4 % range, with Zn- ≈ Cu- > Fe-doped TiO 2. Although the superior performance of the PEO-prepared metal-doped TiO 2 could not be fully confirmed by photoelectrocatalytic oxidation tests of organics, the present investigation showed the viability of DC PEO for the synthesis of metal-doped TiO 2 photoanodes. [Display omitted] • Zn, Cu, Fe doped crystalline TiO 2 films obtained by plasma electrolytic oxidation. • Best photoeletrochemical activity at low doping levels. • IPCE and LSV values exceeding pristine TiO 2. • No straightforward correlation between photoelectrochemical and catalytic activity. [ABSTRACT FROM AUTHOR]