Synergistic effects of thermal-electrochemical Black-TiO₂ceramic nanotubes to enhance visible light photoelectrochemical water splitting

TiO₂photocatalysts are promising for hydrogen production via water splitting; however, their efficiency is limited by a wide band gap and low visible light absorption. This study investigates Black-TiO₂synthesis through a two-step thermal and electrochemical reduction process, introducing oxygen vacancies and Ti³⁺species, which narrow the band gap from 3.2 eV to 2.8 eV, enhancing light absorption and charge transfer. The structural and electrochemical properties of the Black-TiO₂were evaluated using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Mott-Schottky analysis, photocurrent measurements, open-circuit potential (OCP) analysis, and electrochemical impedance spectroscopy (EIS). The Black-TiO₂nanotubes exhibited a photocurrent density of 311 μAcm⁻²at 1.23 V vs RHE, 3.5 times higher than pristine TiO₂, with a 1300-fold increase in charge carrier density, indicating enhanced charge transfer and photoelectrochemical (PEC) performance. This study also provides a comprehensive kinetic analysis of charge transfer and recombination processes, emphasizing the role of defect states in facilitating faster interfacial reactions and improving overall PEC. The findings underscore the potential of Black-TiO₂, produced via a two-step reduction process, as a promising option for efficient PEC water splitting.