Bilayer mesoporous TiO2-based photoanodes: Bandgap engineering, charge transfer dynamics, and photoelectrochemical performance

Bilayer photoanode thin films were fabricated on fluorine-doped tin oxide (FTO) glass by sequential sol-gel deposition of a nanocrystalline TiO 2 bottom layer and a mesoporous Ce-modified TiO 2 top layer with Ce loadings of 2.5 and 5 wt percent (wt%). The structural, optical, electronic and photoelectrochemical properties of the resulting electrodes were systematically characterized by scanning electron microscopy (SEM), ultraviolet–visible (UV–Vis) spectroscopy, and X-ray photoelectron spectroscopy (XPS), Mott-Schottky analysis, electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV) under simulated solar illumination and evidenced the role of TiO 2 mesoporous structure and Ce 3+ /Ce 4+ surface ratio on the enhanced photovoltaic performance. Ce-modified photoanodes exhibited pronounced relative photocurrent gains (239–966%) upon acetate addition, reflecting an electrolyte-selective response of the Ce 3+ /Ce 4+ redox couple. However, in absolute terms the undoped TGP electrode remained the best-performing photoanode (Jsc = 303.8 μA cm −2 , P max = 329.7 μW cm −2 ). These findings establish a quantitative structure–activity relationship between the XPS-determined Ce 3+ /Ce 4+ ratio and the EIS-derived charge-transfer kinetics, providing a rational design framework for Ce-modified TiO 2 photoanodes in solar-driven hydrogen production and photoelectrochemical biomass valorization applications.