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 TiO₂ nanorods (NRs) via a hydrothermal and continuous dip coating method, and then SiP QDs/TiO₂ NRs/Al₂O₃ was obtained by deposition of Al₂O₃ layer through atomic layer deposition technology. The photocurrent density of SiP QDs/TiO₂ NRs/ Al₂O₃ 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 TiO₂ 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 Al₂O₃ passivation layer, which indicates the great potential in the hydrogen generation of solar energy.