Europium-doped amorphous iron oxyhydroxide ultra-thin Nanolayer: A novel architecture for enhancing solar water splitting of bismuth vanadate photoanodes.

Photoelectrochemical (PEC) water splitting provides a sustainable approach for hydrogen generation, yet challenges such as charge recombination and sluggish kinetics persist. Herein, a high-efficiency bismuth vanadate (BiVO) photoanode modified with an ultrathin layer of europium-doped (Eu-doped) amorphous iron oxyhydroxide (BiVO/Eu:FeOOH) as cocatalysts is demonstrated, which is prepared via a facile chemical bath deposition method. The optimized BiVO/Eu:FeOOH photoanode achieves a photocurrent density of 5.77 ± 0.15 mA/cm at 1.23 V vs. reversible hydrogen electrode (V) under Air Mass 1.5 Global (AM 1.5G) illumination, significantly outperforming bare BiVO (0.83 ± 0.15 mA/cm) and BiVO/FeOOH (4.63 ± 0.20 mA/cm). Advanced characterization reveals that Eu-doping forms Eu-O-Fe active sites, alters the Fe coordination environment, and enhances charge separation at the interface. Furthermore, ultrathin Eu:FeOOH coating promotes interfacial water adsorption and optimizes electron transfer during the oxygen evolution reaction (OER). Density functional theory (DFT) calculations show that Eu-doping varies the rate-limiting step from *O → *OOH to *OH → *O, lowering the overpotential. This work establishes a strategy for designing efficient cocatalysts to enhance PEC water oxidation performance.