Oxynitrides are presented as effective non-oxide photocatalysts for overall water splitting. RuO_2-loaded germanium nitride (β-Ge_3N_4) is shown to achieve stoichiometric decomposition of H_2O into H_2 and O_2 under ultraviolet irradiation (λ > 200 nm). A novel solid solution of GaN and ZnO, (Ga_(1-x)Zn_x)(N_(1-x)O_x), with a band gap of 2.4-2.8 eV (depending on composition) achieves overall water splitting under visible light (λ > 400 nm) when loaded with an appropriate cocatalyst. The narrower band gap of the solid solution originates from the bonding between Zn and N atoms at the top of the valence band. The photocatalytic activity of (Ga_(1-x)Zn_x)(N_(1-x)O_x) for overall water splitting is dependent strongly on both the cocatalyst and the crystallinity and composition of the material. The quantum efficiency of (Ga_(1-x)Zn_x)(N_(1-x)O_x) with Rh and Cr mixed-oxide (Rh_(2-y)Cr_yO_3) nanoparticles reaches 2—3% at 420—440 nm, which is the highest reported efficiency for overall water splitting in the visible-light region.
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