A new SiP QDs/TiO2 NRs composite catalyst with Al2O3 passivation layer for enhanced photoelectrochemical water splitting

• SiP QDs was firstly used as a hole-migration cocatalyst for PEC water splitting. • SiP QDs/TiO 2 NRs/Al 2 O 3 showed enhanced PEC activities and stability. • The photocurrent density of composites is 3.29 times that of pure TiO 2 NRs. • Ultra-thin Al 2 O 3 was used as a passivation layer to prevent photo-corrosion. Silicon phosphide (SiP) is a new type of IV–V two-dimensional material with high thermal stability and adjustable bandgap, and it has broad prospects in optics, electricity, and photocatalysis. However, the practical application of SiP for photoelectrochemical (PEC) water splitting was rarely studied. Herein, for the first time, SiP quantum dots (QDs) were introduced as a hole-migration cocatalyst coupled with TiO 2 nanorods (NRs) via a hydrothermal and continuous dip coating method, and then SiP QDs/TiO 2 NRs/Al 2 O 3 was obtained by deposition of Al 2 O 3 layer through atomic layer deposition technology. The photocurrent density of SiP QDs/TiO 2 NRs/ Al 2 O 3 reached 2.14 mA cm −2 at 1.23 V versus RHE, and the IPCE value reached 65.04% at the wavelength of 375 nm under simulated solar light (100 mW cm −2 ); these values are nearly 3.29 and 4.88 times that of pure TiO 2 NRs, respectively. The enhanced PEC properties may be attributed to the enhanced light harvesting capability and the effective transport of photogenerated holes through the synergistic effects between SiP QDs and Al 2 O 3 passivation layer, which indicates the great potential in the hydrogen generation of solar energy.