Atmosphere-dependent hydrogenation of TiO2 nanotubes synthesized via one- and two-step anodization for enhanced photoelectrochemical performance

• TSA-H shows only 4% photocurrent decay after prolonged UV illumination. • Two-step anodized TiO 2 nanotubes exhibit superior photocurrent stability. • Defect engineering in pure H 2 boosts donor density to 3.51 × 10 22 cm −3 . • PEC performance is more sensitive to H 2 atmosphere than anodization method. • XPS confirms highest oxygen vacancies in TSA-H, enhancing charge transport. This study investigates the influence of hydrogenation atmosphere on the physicochemical and photoelectrochemical (PEC) properties of TiO 2 nanotube arrays fabricated via one-step (OSA) and two-step anodization (TSA). After anodization, samples were thermally hydrogenated at 500 °C under pure H 2 , H 2 /N 2 (10%/90%), and H 2 /Ar (10%/90%) atmospheres. All samples retained the anatase phase with highly ordered nanotubular morphology. X-ray photoelectron spectroscopy revealed varying oxygen vacancy (O Vs ) concentrations, highest under pure H 2 . UV–Vis and PL analyses confirmed band gap narrowing due to defect-induced mid-gap states. PEC measurements showed enhanced photocurrent densities of 477 µA/cm 2 (OSA-H) and 475 µA/cm 2 (TSA-H) at 1.23 V vs. RHE, with photoconversion efficiencies up to 3.01%. Electrochemical impedance spectroscopy and Mott–Schottky analysis indicated reduced charge transfer resistance and elevated donor density (N d ), with TSA-H reaching 3.51 × 10 22 cm −3 . Despite similar photocurrent outputs, TSA-H exhibited superior stability with only 4% decay, nearly 2.5 × lower than OSA-H. These findings demonstrate that while both the anodization strategy and the hydrogenation atmosphere affect performance, the latter plays a more dominant role in defect modulation and PEC enhancement, with pure H 2 treatment yielding the most conductive and stable TiO 2 photoanodes.