Electrochemical Deposition of NiCr Alloys from Ethylene Glycol and DES Containing Choline Chloride and Ethylene Glycol or Urea

Abstract The electrochemical deposition of NiCr alloy coatings from the solutions of Ni II and Cr III chloride hexahydrates in the ethylene glycol (EG) and deep eutectic solvents (DES) containing choline chloride (ChCl) and EG (ethaline) or ChCl and urea (U) (reline) was studied. It was found that NiCr coatings with chromium content of 13.0–48.0 wt.% are deposited in galvanostatic mode only from the reline solution at Ni II :Cr III molar ratio equal to 1:4 at 70 °C. Even with a one and a half‐fold rise of Cr III ions concentration in the EG and ethaline, it was not possible to increase the chromium quota in the alloy to more than 1.4 wt.%. The results of electrochemical studies, spectrophotometry in the ultraviolet, visible and IR regions showed that a significant increase in chromium content in the alloy was achieved just in the reline solution owing to the inclusion of U molecules as a ligand in the composition of Ni II and Cr III complex ions. This complexation reduces the overvoltage of Cr III reduction and suppresses thermochromic transition of octahedral polyligand Ni II complexes to the tetrahedral monoligand chloride complex ions at elevated temperatures, which facilitates the reduction of Ni II .