Electrochemical studies on the reduction of uranyl ions in nitric acid-hydrazine media

• Kinetic parameters were determined for U(VI) reduction at various electrodes.
• UO22 + reduction was charge transfer and diffusion controlled at very low acidity.
• UO22 + reduction was kinetically controlled with increase in acidity.
• Current & conversion efficiencies were compared for UO22 + reduction at Ti cathode.
• Electro-reduction of U(VI) by constant potential was energy efficient process.

The redox behaviour of uranyl ions (UO22 +) in nitric acid and nitric acid-hydrazine media were investigated by the transient electrochemical techniques cyclic voltammetry (CV) and chronopotentiometry (CP), at the working electrodes platinum, gold, titanium and glassy carbon (GC) at 298 K. At a very low concentration of 0.05 M nitric acid and in the absence of hydrazine, the reduction of uranyl ions was found to be under charge transfer and diffusion control. Nevertheless, as the acidity of the supporting electrolyte increased, the reduction was purely under kinetic control. The diffusion coefficient (Do) values for the reduction of U (VI) at the working electrodes platinum, gold GC as well as Ti were determined. The current efficiency and conversion efficiency for the reduction of uranyl ions were found to be better under constant potential conditions than that at constant current conditions.