The photocatalytic water splitting using CuxO film on metallic structures under visible light illumination is investigated. A plasmonic enhanced layer is applied for high efficient light harvest and to form a heterojunction to prolong the lifetime of the photogenerated electron-hole pairs. Although CuxO is a potential photocatalyst with high efficiency, it suffers from serious photocorrosion. The photocorrosion mechanism of p-type CuxO has been investigated using x-ray photoelectron spectroscopy. Through analyzing the composition of CuxO during a photocatalytic water splitting reaction, it is found that the photocorrosion of Cu2O on Pt is caused by the reduction of Cu2O to Cu, while the photocorrosion of Cu2O on Au is caused by the oxidation of Cu2O to CuO.