The role of electrolyte ratio in electrodeposition of nanoscale FeCr alloy from choline chloride-ethylene glycol ionic liquid: A suitable layer for corrosion resistance

Abstract Nanoscale Fe Cr alloy is successfully electrodeposited in choline chloride-ethylene glycol (ChCl-EG, mole ratio 1:3) deep eutectic solvent (DES) at two-electrode system by optimizing concentration ratio cFe(II)/cCr(III). ESI-MS analyses indicate [Fe(H2O)3(Cl−)3]− and [Cr(H2O)2Cl4]− are the dominant species of Fe(II) and Cr(III) in ChCl-EG DES, respectively. Linear sweep voltammetry demonstrates that with the increase of cFe(II)/cCr(III) from 1:5 to 1:1, the reduction potential difference between Fe(II) and Cr(III) will become smaller, which is conducive to the electrodeposition of Fe Cr alloy deposit with a higher Cr content. The reduction of Fe(II) or Cr(III) on glassy carbon electrode is a quasi-reversible process controlled by diffusion with a diffusion coefficient of 5.34 × 10−6 cm2·s−1 and 2.22 × 10−6 cm2·s−1. FE-SEM observation shows that as the cFe(II)/cCr(III) decreases from 1:2 to 1:5, the microstructure becomes uneven with the morphology transform from homogeneous particles to scaly blocks. At 1:2, the prepared nanocrystalline Fe Cr alloy has a symmetrical element distribution with a mean coating thickness of 120.3 μm and a mean diameter of ≈1.56 nm. Corrosion resistance test manifests the prepared Fe Cr alloy possesses good corrosion resistance. All the above studies provide a theoretical foundation for Fe Cr alloy production by varying electrolyte ratios.