Effect of PEG 400 on Zn-Cr Alloy Electrodeposition

The effect of poly(ethylene glycol) (PEG) with molecular mass 400 (PEG 400) on the hydrogen evolution reaction (HER) and on the Zn reaction in a Na2SO4 solution and a Zn2+-containing electrolyte was investigated by electrochemical methods. The major effect of PEG 400 on the cathode process was in the range of HER from H2O and bulk deposition of Zn. In the electrolyte for Zn-Cr alloy deposition, the polarization effect of PEG 400 is not sufficiently strong in the potential range of Cr codeposition with Zn, as a result of which the average amount of Cr incorporated in the coatings is relatively low, up to 6 mass %. Based on X-ray photoelectron spectroscopy and X-ray diffraction analysis, it is assumed that Cr is present as metallic Cr in the coatings under the surface hydroxide oxides. Major constituents of the Zn-Cr coatings are two hexagonal phases: eta-(Zn,Cr) and delta-Zn,Cr). Also considering experiments under the industrial conditions of high electrolyte flow and high current density, it is concluded that PEG 400 is not a suitable additive for the electrodeposition of Zn-Cr alloy coatings.