Photoelectrochemical water splitting on chromium-doped titanium dioxide nanotube photoanodes prepared by single-step anodizing

Graphical abstract: Current–potential curves with chopped light measured in 1 M NaOH with a scan rate of 5 mV s⁻¹ for the different samples. - Highlights: • Cr-doped TiO₂ nanotube layers (Cr–TiO₂NTs) were synthesized by anodizing of titanium in a single-step process. • Photoelectrochemical water splitting of Cr–TiO₂NTs is higher than that of pure TiO₂ nanotubes (TiO₂NTs). • Quantity effect of chromium in these composite for photoelectrochemical water splitting is investigated. • Maximum hydrogen production of 37 μL/cm² after 240 min is obtained. - Abstract: Cr-doped TiO₂ nanotubes (Cr–TiO₂NTs) with different amounts of chromium were obtained directly by the electrochemical anodic oxidation of titanium foils in a single-step process using potassium chromate as the chromium source. The effects of chromium amount in anodizing solution on the morphologies, structure, photoabsorption and photoelectrochemical water splitting of the TiO₂ nanotube array film were investigated. Diffuse reflectance spectra showed an increase in the visible absorption relative to undoped TiO₂NTs. The photoelectrochemical performance was examined under visible irradiation in 1 M NaOH electrolyte. Photo-electrochemical characterization shows that chromium doping efficiently enhances the photo-catalytic water splitting performance of Cr-doped TiO₂ nanotube samples. The sample (Cr–TiO₂NTs-1) exhibited better photo-catalytic activity than the undoped TiO₂NTs and Cr–TiO₂NTs fabricated using other chromium concentrations. This can be attributed to the effective separation of photogenerated electron–hole upon the substitutional introduction of appropriate Cr amount in to the TiO₂ nanotube structure