Electron spin resonance and x-ray photoelectron spectroscopic studies on an electrochemically deposited film of mixed manganese/vanadium oxides

Abstract

A thin film of mixed manganese and vanadium oxides was formed on a platinum electrode by electro-oxidation of Mn²⁺ precursors in aqueous solution with VO₃⁻. X-ray analysis revealed that the film consists of an amorphous phase including trivalent and tetravalent Mn ions. The infrared spectrum exhibited the bands attributable to V₂O₅, suggesting that protonation and dehydration of VO₃⁻ occur to form the polymeric structure. The mixed oxide film showed no electron spin resonance signal in an as-deposited state. After the film-coated electrode was immersed into water and then dehydrated, however, a characteristic signal (g = 2.022) of Mn²⁺ in the solid phase appeared, accompanying a decrease in the vanadium content. This suggests that Mn³⁺ ions not in the oxide network, but pairing with unreacted VO₃⁻, are disproportionated to MnO and MnO₂ by the reaction with water, while the VO₃⁻ is diffused to keep the charge valance of the film.