Critical Current Density for Zinc Electrowinning on Various Kinds of Metal Electrodes.

Factors determining the magnitude of critical current density, at which Zn began to deposit from impurityfree electrowinning bath, were studied on the basis of extra-overpotentials peculiar to hydrogen evolution. Electrochemical condition, which permitted codeposition of electrochemically less noble Zn with more noble hydrogen, revealed a kinetic requirement that the deposition overpotential, nH, for hydrogen should be generated at the critical current density to polarize the cathode to reach the equilibrium potential of Zn. The nH was not caused