Abstract:

In flow concentrated acidic electrolytes of cupric sulfate, the effects of concentration of H₂SO₄, CuSO₄ and temperature on the electrochemical performance of Cu/Cu²⁺ electrodes on the graphite substrate were investigated by electrochemical measurements combined with scanning electron microscope(SEM) techniques. The results show that the electrode reaction of deposition-type copper electrodes is controlled by the cathodic process. The kinetics is relatively slow at room temperature. But, the copper deposits are compact. The dendritic and spongy growth are not easy to take place. The polarization of copper deposition can be lowered by increasing the concentration of H₂SO₄, CuSO₄ and temperature to some extent, improving the kinetic characteristics of copper deposition. But, an increase in the solubility of CuSO₄ is dependent on the concentration of H₂SO₄. The optimized composition of the electrolyte is 2.5 mol/L H₂SO₄＋0.7 mol/L CuSO₄. The reaction temperature is 45 ℃. Under the optimized condition, the exchange current density of copper deposition/dissolution on the graphite substrate at 45 ℃ is enhanced by one order of magnitude, indicative of favorable kinetics characteristics. As a result, the charge-discharge voltage difference of the deposition-type copper electrode is decreased by nearly 50% and the energy efficiency is beyond 80%. It is expected that the performance of the Cu-PbO₂ acidic single flow battery would be improved further.

Key words: Flow acidic electrolyte, Copper electro-deposition, Graphite substrate, Electrochemical performance