Systematic investigation of ABO₃ perovskite synthesis to generalise a La and Rh co-doping strategy for visible light...

Photocatalysts present a promising method of producing cheap and green hydrogen. However, most highly-efficient photocatalysts are active to only UV light, which is only 4% of the power in sunlight. Consequently, commercial photocatalysis can only be achieved by developing efficient materials active to visible light (47% of sunlight). Co-doping La and Rh into the perovskite oxide, SrTiO₃ is known to create visible light photocatalysts as part of a Z-scheme system. Here, we rationally apply this strategy to SrTiO₃ and five other ABO₃ perovskites. The A and B-site elements (Sr, Ba, Zr, and Ti) were systematically varied within periodic groups to fabricate six different perovskites: SrZrO₃, SrZr_0.5Ti_0.5O₃, SrTiO₃, BaZrO₃, BaZr_0.5Ti_0.5O₃, and BaTiO₃. The elemental composition of the resulting perovskite affected particle size, crystallinity, morphology, and bandgap. All six perovskites were then co-doped with La and Rh and in every case the doped materials demonstrated red-shifted bandgap. Further, four La,Rh co-doped perovskites demonstrated photocatalytic hydrogen production under visible light (405 and 455 nm). Consequently, the La, Rh co-doping strategy was successfully generalised from SrTiO₃ to ABO₃ perovskites. La,Rh:BaTiO₃ exhibited the narrowest bandgap (2.58 eV) and the second highest photocatalytic activity. These properties establish La,Rh:BaTiO₃ as a potential commercial visible-light active photocatalyst.