Herein we present a new p–n heterojunction photoelectrode design utilizing Cu₂O and TiO₂-P25 loaded with only 1 wt% Au@TiO₂ plasmonic core–shell structure for the photoelectrochemical (PEC) process. It is found that the photoelectrode with a sandwich-like layer design, i.e. TiO₂-1 wt% Au@TiO₂/Al₂O₃/Cu₂O, not only promotes light harvesting but also improves charge carrier separation, resulting in drastically improved photocurrent density up to −4.34 mA cm⁻² at −0.2 V vs. Ag/AgCl under simulated AM 1.5 solar illumination, ∼20 fold enhancement compared to that obtained from a TiO₂-P25/Cu₂O photoelectrode. It is also revealed that the photoelectrochemical performance is closely related to the Au nanoparticle size, induced by surface-enhanced scattering of the plasmonic nanoparticles. It should also be noted that these multilayer photoelectrodes also exhibit high stability through rational design of the PEC system to avoid the photocorrosion on Cu₂O layers.