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

Abstract

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 that 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 H2 and O2 gases, although the Rh-metal/(Ga1–xZnx)(N1–xOx) photocatalyst exhibited little activity for overall water splitting due to rapid water formation from H2 and O2 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 H2 evolution on Rh.