Efficient photocatalytic hydrogen production over La/Rh co-doped Ruddlesden-Popper compound Sr2TiO4

Layered semiconductor compounds often exhibit intriguing properties for photocatalytic water splitting, probably correlated with their peculiar crystal structures that facilitate charge separations. In this work, we perform an investigation on the layered Ruddlesden-Popper compound Sr2TiO4 and its La/Rh co-doped counterparts for photocatalytic hydrogen production from water. Their crystal structures, optical absorption and other physicochemical properties have been systematically explored. Our results suggest that La/Rh can be successfully incorporated into Sr2TiO4 with layered crystal structure maintained. The use of polymerized-complex method for sample synthesis significantly reduces the calcination temperature as low as 900 °C. La/Rh serves as efficient dopants for extending the light absorbance of Sr2TiO4 as far as 550 nm. Photocatalytic hydrogen productions are also considerably improved after La/Rh co-doping under both full range (λ ≥ 250 nm) and visible light irradiation (λ ≥ 420 nm). An optimal doping level is reached at 3% (Sr1.97La0.03Ti0.97Rh0.03O4) which gives the highest average hydrogen production rate ∼100 μmol/h and ∼40 μmol/h under full range (λ ≥ 250 nm) and visible light irradiation (λ ≥ 420 nm), corresponding to apparent quantum efficiency ∼1.27% and ∼1.18%, respectively. Photoelectrochemical analysis reveals that charge separation and electron lifetime strongly depends on the level of La/Rh co-doping. Mott-Schottky analysis and theoretical calculations indicate that the improved light absorption of La/Rh co-doped Sr2TiO4 stems from the formation of new valence band with Rh 4d character which uplifts the valence band edge of Sr2TiO4.