Electrochemical Impedance Spectroscopy Study on Electrodeposition of Chromium in Sargent Bath.

The mechanism of electrodeposition of Cr in a Sargent bath was investigated with electrochemical impedance spectroscopy (EIS). Cr(VI)sol is reduced to Cr via two reaction intermediates, i.e., Cr(III)ad and Cr(II)ad. The current-potential curve for Cr(VI)sol reduction can be divided into three potential regions. Inductive semicircles were observed on the Nyquist plots of electrochemical impedance measured in two potential regions, where it was found that the inductive behavior originates from the actions of Cr(III)ad and Cr(II)ad. Moreover, results indicate that the hydrogen evolution influenced the Cr(VI)sol reduction rate. The simulated results on the basis of the reaction model as outlined are in agreement with the experimental results.