Electrochemical behavior and electrodeposition of Fe-Co-Ni thin films in choline chloride/urea deep eutectic solvent

Fe-Co-Ni coating, a vital type of transition metal alloy, shows great potential in the field of hydrogen storage and magnetic materials. In this study, Fe-Co-Ni coatings were prepared on Cu substrates from a deep eutectic solution of choline chloride/2Urea (ChCl/2Urea) DES by electrodeposition. The effects of deposition potential on the morphology, chemical composition, crystal structure, corrosion resistance and magnetic properties of nanostructured Fe-Co-Ni coatings were investigated. The results revealed that the reduction process of Fe-Co-Ni alloy on the Cu electrode in ChCl/2Urea DES was irreversible three-dimensional instantaneous nucle-ation, which was controlled by diffusion. The surface morphology, microstructure, compose and crystallite size of the Fe-Ni-Co alloy were related to the deposition potential. The Fe content of the electrodeposited alloys showed a maximum of 48.17 at% at the applied potential of -1.3 V and a positive correlation was observed between the Fe content and electrodeposition potential in the investigated potential range. The nickel-rich coatings were obtained at high potential and iron-rich coatings were obtained at low potential. The less rough-ness, more compact grain and uniform flat Fe-Co-Ni coatings were prepared under a more negative potential. The Fe-Co-Ni coatings were composed of face-centered cube (fcc, NiFe) and body-centered cube crystals (bcc, FeCo). With the negative shift of deposition potential, the structure of Fe-Co-Ni coatings grew preferentially toward FeCo(1 1 0) and FeCo(2 1 1) crystal surfaces. The Fe-Co-Ni coatings prepared from ChCl/2Urea DES at different deposition potentials showed good corrosion resistance. Fe-Co-Ni coating that is produced at the deposition potential of -1.2 V, exhibited a more positive corrosion potential and obvious magnetic anisotropy.