In situ surface Raman spectroscopy study on Fe-Mo alloy induced-codeposition

Abstract

The Fe-Mo alloy induced-codeposition has been studied by in situ surface Raman spectroscopy. In the solution containing 0.2 mol.L-1 Na2MoO4, pH = 4.0, the Raman spectra showed three peaks at 940, 880 and 450 cm(-1) corresponding to polymolybdates species on the surface, at open circuit potential and -0.3 V(vs SCE). At the potential < -0.5, new peaks at about 730, 560, 510, 470 cm(-1) appeared in the spectra while a blue film was observed on the surface, which can be attributed to mixed-oxidation molybdenum oxides formation. The peak at 730 cm(-1) did not disappear even when the potential moved to -1.9 V, indicating the film cannot be further reduced. But in the solution of Na2MoO4 containing 0.1 mol.L-1 FeSO4 and 0.2 mol.L-1 citric acid, the peak of the mixed-oxidation oxides shifted to 740 cm(-1). And this peak could fade away gradually in the potential region from -1.3 to -1.9 V while a silver-white deposit emerged on the surface. The results showed that the structure of the mixed-oxidation Mo oxides film codeposited with Fe2+ was different from that of the film deposited without Fe2+. The former can be further reduced to form Fe-Mo alloy.