The redox behavior of vanadium in alkaline solutions by cyclic voltammetry method

The redox behavior of vanadate ions in alkaline solutions has been studied with NaOH concentration ranging from 0.1 M to 1 M. The cyclic voltammetry results reveal that vanadate ions are irreversibly reduced to V(OH)2 via a three-electron transfer reaction, and the first electron transfer reaction is the rate-determining step. The oxidation processes involve the stepwise oxidation of V(OH)2 to V(OH)3, and V(OH)3 to vanadate ions. The reduction kinetics is discussed and the diffusion coefficient of vanadate ion is calculated to be 1.40 × 10−9 m2/s. Chemical and XPS analysis results suggest that due to the instability of the direct reduction product V(OH)2, the obtained deposits after reducing electrolysis are mixed-valence (+3/+4) vanadium compounds with an empirical compound formula of VO1.87·1.38H2O. X-ray diffraction and TGA/DSC analysis results further confirm that the collected reducing electrolysis products are amorphous hydrated vanadium compounds.

► Three-electron vanadate ion reduction reaction has been confirmed.
► The diffusion coefficient of vanadate ions in alkaline solutions is calculated.
► Reduction products are easily oxidized to form mixed-valence vanadium compounds.