We report a new electrochemical route for fabricating molybdenum and vanadium mixed oxyhydroxide films on Au electrode from Keggin-type vanadium-substituted polymolybdophosphate. The process involves a potentiodynamic reduction of aqueous 9-molybdo(VI)-3-vanadophosphosphate(V) ([PMo9V3O40](6-)) in the potential region between 0 and -0.7 V versus Ag/AgCl. The resulting Mo-V oxyhydroxide film electrode gave a stable redox behavior in Na2SO4 electrolyte of pH 3. X-ray photoelectron spectroscopy revealed that this results from oxidation/reduction of Mo5+/Mo6+ in the film which accompanies extraction/insertion of protons for charge compensation. The deposited V ions remained in the film upon repetitive potential cycling without affecting their oxidation state. Voltammetric data in the presence of sodium nitrite showed electrocatalytic activity of the Mo-V oxyhydroxide toward the electroreduction of nitrite. (C) 2005 Elsevier Ltd. All rights reserved.