Effect of lanthanide (La, Nd, Gd) doping on the structural and photoelectrochemical properties of WO3 thin films synthesized by sol-gel

In this study, WO3 and 2 at.% WO3:Ln (Ln = La, Nd, Gd) thin films were prepared by sol-gel, from a novel and highly stable precursor solution based on tungstic acid. The structural characterization of the films is consistent with the dopant atoms occupying interstitial positions in the crystal lattice, leading to modifications in the preferential orientation from the (200) to the (002) plane of the monoclinic phase of WO3. The lanthanide doping reduces the band gap, enhancing the photoelectrochemical properties. Electrochemical impedance spectroscopy measurements show that the lanthanide dopants reduce the charge-transfer resistance and enhance the hole lifetime in WO3; furthermore, the Mott-Schottky analysis shows an increase in the donor density (ND) values. These results suggest that doping with La, Nd and Gd is a favorable strategy to improve the efficiency of WO3 photoanodes, helping to elucidate which element most effectively enhances its photoelectrochemical properties.Graphical abstractInfluence of the La, Nd and Gd doping on the preferred (200) plane orientation of the monoclinic WO3 thin films and its effect on the photoelectrochemical current density