Template Electrochemical Growth and Properties of Mo Oxide Nanostructures

Abstract

This work is aimed at studying the growing process of nanostructures electrodeposited from molybdate aqueous solutions at different pH values into pores of polycarbonate membrane templates. The challenging issue was the opportunity to investigate a rather complex deposition process in a confined ambient, where electrochemical conditions are quite different from those usually established for deposition on a flat substrate. Nanostructures were grown from a bath containing Mo7O246– (NH4)6Mo7O24·4H2O) at different concentrations (50–100 g/L), at a constant cathodic current density of 2 mA/cm2 (electrodeposition area ∼8 cm2). Nanostructured deposit was characterized by XRD, EDS, Raman, XPS, and photoelectrochemical spectroscopy. Several parameters have been investigated, such as electrodeposition time, concentration of Mo precursor, and pH. These parameters do not influence the nature of deposit that always consists of mixed valence molybdenum oxides, whereas the nanostructure morphology changes with pH. Nanostructures were found amorphous and consisting mainly of MoO2 underneath α-MoO3. Photoelectrochemical spectroscopy revealed n-type conductivity and two linear regions in the (Iph·hν)0.5 vs hν plot, giving optical gaps of 2.5 and 3.2 eV, typical of MoO2 and α-MoO3, respectively. To our best knowledge, this is the first paper dealing with the fabrication of a uniform array of MoO2/MoO3 core–shell nanowires by template electrosynthesis.