亜鉛電析の臨界電流密度に及ぼす不純物の相乗作用

Abstract

The synergistic effect of the impurities on the critical current density for Zn deposition was investigated by measuring the polarization curves in the solutions containing different impurity elements. The critical current density for Zn deposition was significantly increased in the solution containing both Cu2+ and iron-group metal ions. It has been reported that the deposition of iron-group metals was suppressed in the presence of Zn2+ ions due to the adsorption of Zn hydroxide formed on the cathode. Since it was found that Co easily deposited on Cu area of coupled Cu-Zn electrode, the role of Cu is considered to promote the suppressed iron-group metals deposition by providing the iron-group metal ions with an active sites not adsorbed by Zn hydroxide. The synergistic effect of the impurities was also found in the solution containing a very small amount of Sb and iron-group metal ions. Sb existing in oxide state seemed to work as a catalyst to reduce the inherent deposition overpotential of iron-group metals. Thus, Cu2+ and Sb seem to promote the kinetically suppressed deposition rate of iron-group metals to decrease the hydrogen overpotential of cathode substrate, resulting in the increase in the critical current density for Zn deposition.