A photocatalyst and a method for producing hydrogen and oxygen from water by photocatalytic electrolysis are disclosed. The photocatalyst includes a photoactive material and metal or metal alloy material (15)—e.g. pure particles or alloys of Au, Pd and Ag—capable of having plasmon resonance properties deposited on the surface of the photoactive material. The photoactive material includes a p-n junction (17) formed by contact of a n-type semiconductor material (10), such as mixed phase TiO2 nano particles (anatase to rutile ratio of 1.5 to 1 or greater), and a p-type semiconductor material (16), such as CoO or Cu2O.