Spectroscopic study of vanadium(V) precipitation in the vanadium redox cell electrolyte

In this study, characterisation of vanadium electrolyte and vanadium(V) red precipitate formed in the positive half-cell electrolyte of a vanadium red ox cell is present using different spectroscopic techniques. V-51 solution NMR showed that the main peak at about - 545 ppm in the spectra of the redo x electrolyte could be attributed to the monomer species of V-2(+) ions and the intensity of the peak decreased with both temperature and aging time. These results confirmed the formation of a red precipitate in the redox ele ctrolyte due to polymerisation of the monomer species of V-2(+) in the stro ng acidic media at elevated temperatures and with aging. Electron spin reso nance (ESR) measurements showed that V(IV) ions were also present in the el ectrolyte. The presence of V(IV) ions may play an important role in the sta bility of the electrolyte. The static solid state V-51 NMR spectrum of the thermal precipitate dried at room temperature showed a peak at - 243 ppm. w hich is characteristic of V(V) in distorted octahedral oxygen coordination similar to that formed for crystalline and gel forms Of V2O5. Characteristi cs of V2O5 were also identified by X-ray diffraction (XRD) and had a fibrou s morphology before heating. However, transition electron microscopy (TEM) showed that conversion of the fibrous morphology of V2O5 to the small cryst alline morphology of V2O5 occurred after heating at 520 degreesC. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.