Lanthanoid Oxide Layers on Rhodium-Loaded (Ga1-xZnx)(N1-xOx) Photocatalyst as a Modifier for Overall Water Splitting under Visible-Light Irradiation

Lanthanoid oxide modifier layers were applied to Rh metal nanoparticles on (Ga1-xZnx)(N1-xOx) photocatalyst for overall water splitting under visible-light irradiation. Structural analysis by transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy revealed than lanthanoid(III) oxide layers coated the Rh nanoparticles on (Ga1-xZnx) (N1-xOx), although they were also deposited directly on the (Ga1-xZnx) (N1-xOx) surface. Certain lanthanoid oxide layers (La, Pr, Sm, Gd, and Dy) functioned as modifiers for Rh-metal/(Ga1-xZnx)(N1-xOx) to produce H-2 and O-2 gases, although the Rh-metal/(Ga1-xZnx)(N1-xOx) photocatalyst exhibited little activity for overall water splitting due to rapid water formation from H-2 and O-2 on Rh. Ce and Eu oxide layers showed no photocatalytic activity, most likely due to their ability to capture photoexcited electrons from Rh metal/(Ga1-xZnx)(N1-xOx). The enhancement of photocatalytic activity by lanthanoid oxide loading was shown to be dependent on the formation of redox-inactive lanthanoid(III) oxide layers on the Rh nanoparticles, which effectively suppresses the backward water formation reaction to enable H-2 evolution on Rh.