Synergistic Regulation of Bulk and Surface Properties Promoting Carrier Separation and Transport in Cu ₂ O Photocathode

Cu ₂ O is a promising p‐type semiconductor for photoelectrochemical (PEC) hydrogen production owing to its suitable band structure and high theoretical photocurrent density. However, its practical application is limited by fast photogenerated carrier recombination and severe photocorrosion. In this work, a NiO _x /Cu ₂ O‐A/CeO ₂ sandwich‐structured photocathode was fabricated. Based on their electric structure with favorable interfacial band alignment, NiO _x and CeO ₂ play a role as hole transport and electron transport layer to accelerate Cu ₂ O surface carrier separation, respectively. Meanwhile, annealing induces in situ formation of Cu nanoparticles within Cu ₂ O, improving Cu ₂ O bulk electron extraction and carrier separation. CeO ₂ simultaneously acts as protective coating, suppressing surface recombination and photocorrosion. The optimized NiO _x /Cu ₂ O‐A/CeO ₂ photocathode delivers a photocurrent density of 3.1 mA/cm ² at 0 V versus RHE, more than ten times higher than pure Cu ₂ O, with a maximum IPCE of 33.1%. Moreover, it retains 68% of its initial current after 5 h operation, exhibiting markedly improved stability. Electrochemical and optical analyses indicate that the multilayer architecture synergistically modulates surface charge transport, prolongs carrier lifetime, enhances separation and injection efficiencies. This work demonstrates a simple and low‐cost strategy for constructing efficient and stable Cu ₂ O‐based photocathodes.