Enhanced Photoelectrocatalytic Water Splitting at Hierarchical Gd³⁺:TiO₂Nanostructures through Amplifying Light Reception and Surface States Passivation

The influence of rare earth gadolinium (Gd3+) ion doping on optical and photoelectrochemical properties of TiO2 is studied. The hierarchical clump-type TiO2 nanostructure was fabricated using poly-vinyl acetate as soft-template. The optical absorbance quantity of TiO2 was strikingly promoted at bandgap energy region (380 nm) by Gd3+ doping, as well as it extend a wide absorbance in visible wavelength region (400 – 800 nm) elucidating the sub-bandgap formation. As a result, Gd3+:TiO2 exhibits high photocurrent density than undoped TiO2 in photoelectrocatalytic experiments. Another plausible reason for enhancing the photocurrent density at Gd3+:TiO2 was analyzed through electrochemical impedance spectroscopy. The underlying mechanism of surface states controlled charge transfer at TiO2/electrolyte interfaces affected the photoelectrocatalytic hydrogen fuel generation, and compete with Gd3+ ion doping through bottlenecking of photoelectrons trapping at surface states. The improved charge separation (e−/h+) at Gd3+:TiO2 result effective photoelectron collection and thus yield 180 % higher hydrogen gas (∼ 2.34 mL.h−1.cm−2 ) generation compare to pristine TiO2 (1.28 mL.h−1.cm−2) under UV light irradiation. The improved optical and charge transfer characteristics of hierarchical TiO2 by Gd3+ ions can be implemented to wide range of other metal oxide based photocatalytic fuel generation.