Electrodeposition of Ni–Co alloys from a deep eutectic solvent

Pure Ni and three Ni–Co alloys films, i.e. Ni–4 wt.%Co, Ni–18 wt.%Co, and Ni–40 wt.%Co, are electrodeposited at room temperature from the choline chloride/ethylene glycol deep eutectic solvent dissolved by nickel or/and cobalt chlorides. Electrodeposition mechanism, microstructure, and corrosion properties of the films are investigated. Surface morphology and chemical composite of the films are significantly dependent on the Ni2+ and Co2+ concentrations in the electrolytes. Interestingly, it is found that the amount of cobalt in the Ni–Co alloy films is significantly lower than that present in the electrolytes, which indicates an absence of anomalous codeposition process for the non-aqueous electrolytes. However, anomalous codeposition of Ni–Co deposits is frequently observed for the aqueous electrolytes. The Ni–Co alloy films possess face-centered cubic structures and refined grains revealed by X-ray diffractometer and scanning electron microscope. Potentiodynamic polarization measurements show that the Ni film exhibits the noblest corrosion potential and the lowest corrosion current compared with the Ni–Co alloys films. Moreover, the more Co content the Ni–Co films have, the more negative corrosion potential and the higher corrosion current the films exhibit.

► Electrodeposition of Ni–Co films from a deep eutectics system.
► Co2+ concentrations influence surface morphology and chemical composite of films.
► Ni–Co deposition with a non-anomalous codeposition process.