Engineered Fe2O3/TiO2/Carbon-Dots Heterostructures for Enhanced Photoelectrochemical Water Oxidation

Abstract Hematite (α-Fe2O3) is an abundant, low-cost visible-light absorber and a leading photoanode candidate for solar-driven water splitting, yet its conversion efficiency remains constrained by poor charge transport, fast electron–hole recombination, and sluggish oxygen evolution reaction (OER) kinetics. Here, we engineer a Fe2O3/TiO2/Carbon-dot (C-dot) photoanode built on an FTO substrate that addresses these bottlenecks through a defined layer architecture: hydrothermally grown Fe2O3 nanorods provide visible-light absorption, a sol–gel-deposited mesoporous TiO2 overlayer passivates the hematite surface, and finally solvothermally grown C-dots decorate the outer surface to drive interfacial charge transfer. Structural and chemical characterization confirms a well-integrated, intimately contacted heterostructure, while optical measurements show that C-dot incorporation broadens visible-light harvesting without altering the underlying optical band gap (∼2.1 eV) indicating that any performance gain originates from charge-transport rather than band-structure effects. Under photoelectrochemical testing, the Fe2O3/TiO2/C-dots photoanode delivers substantially higher OER photocurrent than the Fe2O3/TiO2 baseline across the full UV-to-visible illumination range, with simulated-solar photocurrent density increasing by approximately 2.5-fold at neutral pH and by approximately 3.4-fold under alkaline conditions, pH 14, where OER kinetics are most favorable. The device sustains stable, reproducible photocurrent over multi-hour continuous solar illumination in both electrolytes, supporting its operational robustness under realistic water-splitting conditions. Mechanistically, Mott–Schottky analysis shows that C-dot incorporation more than doubles the carrier density (from 1.6 × 1020 to 3.3 × 1020 cm–3), while electrochemical impedance spectroscopy reveals a ∼27% reduction in interfacial charge-transfer resistance, together identifying enhanced carrier density and accelerated interfacial charge transfer, rather than band-edge modification, as the origin of the improved device performance. These results establish C-dot functionalization as a simple, scalable strategy for boosting the photocurrent and operational stability of Fe2O3/TiO2 photoanodes, with direct relevance to the design of higher-performing, low-cost solar-to-fuel conversion devices for water oxidation and solar hydrogen production.