Intermediate molybdenum oxides involved in binary and ternary induced electrodeposition

Molybdenum oxides have been produced by electrodeposition in sulphate medium from solutions containing molybdate, in the presence or in the absence of citrate, Co(II) and Co(II) + Ni(II). The goal of this work was the characterisation of intermediate molybdenum oxides able to progress to Co–Mo and/or Co–Ni–Mo electrodeposits. For this purpose, several oxide layers were prepared on ITO/glass and silicon-based substrates and characterised by UV–Vis, X-ray photoelectron spectroscopy and X-ray diffraction. The kind of molybdenum oxides that would evolve to the alloy presented a mixed valence state of MoIV and MoV and a certain degree of crystallinity. A yellow-brown-coloured film was observed when a continuous oxide layer was electrodeposited. Inclusion of small amounts of Co or Co + Ni occurred during oxide formation, thereby leading to doped molybdenum oxide layers. There would be two factors that determine the viability of the alloy deposition: the formation of reasonably reduced molybdenum oxides and the interaction between citrate and the other metals (cobalt, nickel) in solution. These requirements would be satisfied at solution pH > 2.