Electrodeposition and characterization of Mo oxide nanostructures

Template electrodeposition has been used to grow uniform arrays of molybdenum oxide nanostructures in polycarbonate membrane. Several parameters have been investigated, like electrodeposition, time and solution pH. These parameters do not influence the nature of the deposit that always consists of mixed valence molybdenum oxides, whereas the nanostructure morphology changes with pH. In particular, at low pH (2.7), nanotubes are formed, whilst arrays of nanowires are obtained above pH 5.5. This change of morphology is likely due to H2 bubbles evolution during the electrochemical deposition, particularly occurring at low pH. It was found that fast removal of H2 bubbles through vigorous stirring of the solution favors the growth of nanostructures with a uniform length. Molybdenum oxide nanostructures were characterized by XRD, EDS, Raman, XPS and photoelectrochemical measurements. Results indicate that nanostructures are amorphous and consist mainly of MoO2 underneath α-MoO3. The presence of these two oxides was confirmed by photoelectrochemical experiments. From photocurrent spectra, two linear regions appear in the (Iph·hν)0.5 vs. hν plot, whose extrapolation to Iph=0 gives optical gaps values of 2.5 and 3.2 eV, which are typical of MoO2 and α-MoO3, respectively. In addition, photoelectrochemical investigation revealed n-type conductivity of this mixed oxide deposit.