The photocatalytic water splitting using 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 is a potential photocatalyst with high efficiency, it suffers from serious photocorrosion. The photocorrosion mechanism of p-type has been investigated using x-ray photoelectron spectroscopy. Through analyzing the composition of during a photocatalytic water splitting reaction, it is found that the photocorrosion of on Pt is caused by the reduction of to Cu, while the photocorrosion of on Au is caused by the oxidation of to CuO.