A Chronocoulometric Method to Measure the Corrosion Rate on Zinc Metal Electrodes

Research studies on zinc metal-based batteries have attracted considerable attention as a candidate for post-lithium-ion batteries. Zinc is one of the few metal anodes that is compatible with aqueous and non-aqueous electrolytes, providing a large theoretical capacity of 820 mAh g^-1. However, in aqueous electrolytes, the zinc metal anode suffers from hydrogen evolution reaction (HER), by which zinc is irreversibly consumed or corroded continually. Exact estimation of the corrosion rate has been a challenge in the development of Zn-based batteries. Measurement of the corrosion rate by conventional Tafel analysis meets serious problems because the cathodic current reflects deposition of Zn metal as well as HER, inhibiting exact measurement of the corrosion rate. Herein, we developed a chronocoulometric "deposition-rest-dissolution" method to quantify the corrosion rate without such interference from the deposition of Zn. The method was successfully applied to the quantification of the rate of chemical corrosion of Zn in aqueous electrolytes with various pH and concentration values. The "deposition-rest-dissolution" method and electrochemical impedance spectroscopy confirmed that saturated ZnSO₄ (ca. 3.2 M) + 0.075 M Li₂SO₄ delivers the lowest corrosion rate compared to the other electrolytes, probably because the activity of water in such a concentrated electrolyte is low enough to suppress the kinetics of HER. Moreover, this method can be generally applied to determine the rate of chemical corrosion on various metal electrodes.