Polyoxometalate anions P2Mo18O626- and P2W18O626- in the form of tetrabutyl ammonium salts, have been immobilized on the surface of wax impregnated graphite (WIG) electrodes, in methyl methacrylate polymeric matrix and graphite powder for electrical contact. Their electrocatalytic behavior toward the reduction of ClO3-, BrO3-, NO2- and O-2 as well as the lack of H-2-evolution and dechlorination of 4-chlorophenol is reported. Cations Li+, Na+, NH4+ and (C2H5)(3)NH+ and pH have a profound effect on cyclic voltammograms. Comparisons are made with the corresponding behavior inhomogeneous solution.