Method for forming a bismuth/tungsten oxide heterostructure film

A method for forming a Co—Pi modified BiVO4/WO3 heterostructure film, comprising:

• direct current reactive sputtering tungsten (W) onto a substrate in a gaseous mixture comprising oxygen to form a tungsten trioxide (WO3) film on the substrate;
• direct current reactive sputtering bismuth (Bi) onto the tungsten trioxide (WO3) film in a gaseous mixture comprising oxygen to form a dibismuth trioxide (Bi2O3) film on the WO3 film;
• drop-casting a vanadyl acetylacetonate solution onto the Bi2O3 film and heating at a temperature of at least 450° C. in ambient air to convert the Bi2O3 film to a BiVO4 film;
• removing V2O5 from the BiVO4 film with an alkali solution;
• wherein the BiVO4 film is a porous film comprising crystalline BiVO4;
• immersing the BiVO4 film on the substrate in an aqueous mixture containing a cobalt salt and a phosphate salt;
• photoelectrochemically coating the BiVO4 film with a cobalt-phosphate (Co-Pi) to form a modified film on the surface of the substrate.