Abstract:A mechanism study on MoO₂ electrodeposition from ammonium molybdate solution was presented via linear sweep voltammetry, species distribution diagram, Raman spectra, Fourier transform infrared spectrometry and X-ray diffractometry. The results show that there exist two reducible species in ammonium molybdate aqueous solution, i.e. and molybdenum ammonium complex. In weak acid medium without , an obvious reduction peak denoting the reduction of to molybdenum(IV) oxides emerges at around -0.7 V (vs SCE). While in neutral and basic solutions without , the dominant species changes to , and accordingly, no reduction peak appears except hydrogen evolution. plays an important role in MoO₂ electrodeposition. A new current peak appears at -1.25 V (vs SCE) in both acid and basic solutions, which is attributed to the reduction of molybdenum complex. The effects of solution composition and the electrodeposition conditions on the current efficiency were discussed systematically. By optimizing the electrodeposition conditions, the current efficiency can reach up to 51.9%.

Key words: MoO₂; NH₄⁺; sodium molybdate; electrodeposition; current efficiency; mechanism