Simultaneous photodeposition of rhodium–chromiumnanoparticles on a semiconductor powder: structural characterization and application to photocatalytic overall water splitting

Abstract

Simultaneous photodeposition of rhodium (Rh) and chromium (Cr) nanoparticles on a semiconductor powder was examined as a means of constructing active sites for hydrogen evolution in photocatalytic overall water splitting. A solid solution of gallium nitride and zinc oxide (GaN:ZnO) powder that catalyzes overall water splitting with visible light was employed as a semiconductor support. The photodeposition was carried out in aqueous suspension containing GaN:ZnO, (NH₄)₃RhCl₆, and K₂CrO₄, and used H₂O as an electron donor. With increasing concentration of K₂CrO₄, the valence state of the codeposited Rh species varied from metallic to trivalent, while that of Cr remained trivalent. At intermediate concentrations of K₂CrO₄, the photodeposits were core/shell-like crystalline nanoparticles consisting of a metallic Rh core and an Rh(III)–Cr(III) mixed-oxide shell. The photocatalytic activity for visible-light-driven overall water splitting (λ > 400 nm) was strongly dependent on the structure of the photodeposits. Comparative experiments using an analogue, modified with core/shell-structured Rh/Cr₂O₃ nanoparticles, revealed that core/shell-structured nanoparticles consisting of a metallic Rh core were better than Rh–Cr trivalent mixed oxides for enhancing the photocatalytic activity.