Eco-friendly preparation of nanocrystalline Fe-Cr alloy coating by electrodeposition in deep eutectic solvent without any additives for anti-corrosion

Abstract

Nanocrystalline Fe-Cr alloy coatings are prepared by electrodeposition in choline chloride-ethylene glycol (ChCl-EG) deep eutectic solvent (DES) by varying cell voltage (2.4–2.8 V) and temperature (333–353 K) without any additives. Cyclic voltammetry demonstrates that Fe(II) and Cr(II) can be co-deposited, also the presence of Fe(II) promotes the reduction of Cr(II). Linear sweep voltammetry reveals that increasing temperature facilitates the reduction of Fe(II) while not to Cr(II). Chronoamperometry verifies the electrocrystallization of Fe(II), Cr(III) and the both on glassy carbon electrode tends to instantaneous nucleation. FE-SEM shows that the microscopic morphology of obtained alloy coating is dense and uniform. With the increase of cell voltage, the grain gradually refines with the microstructure transform from layered-rock to weedy. As the temperature decreases, the surface becomes homogeneous with the morphology range from weedy to granular. HR-TEM indicates that the product obtained at 2.8 V and 333 K composed of compact and grained surface has an average particle size of ≈1.53 nm with polycrystalline structure. EDS, XRD and XPS spectrum prove it is pure with a passive film composed of Cr2O3 and Fe2O3 on the surface. Tafel polarization test confirms the as-prepared alloy coating possesses excellent corrosion resistance. All these findings promise an eco-friendly and simple route for the cleaner production of nanocrystalline Fe-Cr alloy coating with excellent corrosion resistance at near room temperature without any additives.