Photoelectrocatalytic behavior of electrodeposited zinc ferrite films with varying Zn:Fe ratio

We report on stoichiometrically varied zinc ferrite films prepared by electrochemical deposition which can potentially be used as photoanodes in solar water splitting cells. The ferrite films are prepared from an electrodeposition bath containing iron and zinc ions in the presence of triethanolamine as a complexing agent. The ratio of Zn to Fe is controlled by fine tuning of the deposition potentials and the concentrations of the two metal ions. The film thickness is monitored by the time of deposition or the charge passing during the deposition process. The deposited films are amorphous and converted to highly crystalline oxides by post thermal treatment at 600 degrees C. Structural and morphological characterization was performed by transmission electron microscopy and X-ray diffraction. Raman spectroscopy was used to locally identify the phase compositions. The surface composition and the chemical state of the species were investigated by X-ray photoelectron spectroscopy which shows that the surface composition of some films is different from the bulk. Photoelectrochemical measurements show that the ferrites are n-type semiconductors and the onset and the magnitude of the photocurrent is strongly dependent on the ratio Zn:Fe at the surface. Photoelectrodes containing understoichiometric amount of zinc at the surface (Zn:Fe ratio = 0.25-0.40) exhibit higher photocurrents than those being stoichiometric or slightly excessive in zinc.