Abstract
The possibility to use highly saturated acetate bath to electrodeposit the mixed-phase materials containing Mo oxides has been investigated. The XRD characterization revealed that the as-deposited coatings are amorphous and consist only of MoO2 and MoO3 phases without traces of metallic Mo phase. This statement has been supported by XPS measurements, which reveal the presence of three different molybdenum oxidations states in electrodeposits: Mo4+, Mo5+ and Mo6+. It was found that the Mo6+ state prevails with 41% of total contribution, whilst Mo5+ and Mo4+ contribute to 28 and 31%, respectively. The deposits retain an amorphous structure up to 800°C; while molybdenum at this temperature is predominantly oxidized to the Mo6+ state (91%). These results, coupled to those of SEM and EDS, revealed that concentrated acetate bath could be used mainly for the formation of the mixed valence molybdenum oxide film unlike to the deposition of the metallic Mo phase.
Highlights
Molybdenum oxide (MoOx) thin films exhibit interesting structural, chemical, electrical and optical properties [1, 2], and it makes them attractive to use them in a new type of technological devices
As the current started flowing through the system, the cathode was covered by a light grey layer and an intense instantaneous foaming of the solution due to the enormous hydrogen evolution has been observed
The scanning electron microscopy (SEM) images show that the deposit is not uniform and the Cu substrate is not covered continuously; various sizes nodules and multiple cracks were detected (Fig. 1a, b)
Summary
Molybdenum oxide (MoOx) thin films exhibit interesting structural, chemical, electrical and optical properties [1, 2], and it makes them attractive to use them in a new type of technological devices. XPS has been clearly useful in monitoring changes in elemental oxidation states and in stoichiometry during various processes. In the light of these advantages, MoOx thin films have been deposited from aqueous peroxo-polymolybdate [13], sodium molybdate [14] and ammonium-heptamolybdate [15] solutions. In this case, the electrodeposited films consist of mixed valence oxides containing Mo+4, Mo+5 and Mo+6 [16,17,18]. The literature review indicates that the catalytic properties and composition of electrolytic molybdenum oxide films are closely related to electrolyte composition, electrolyte pH and applied potential/current density
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