Using an organic-based electrolyte bath in electropolishing of pure metallic nickel and cobalt at the nanoscale

This study presents a successful electropolishing process applied to two highly valuable metals, namely nickel and cobalt, within a choline chloride-lactic acid eutectic mixture at a mole ratio of 1:2. The electrochemical investigation encompassed the acquisition of voltage-current (V-I) and current-time (I-t) profiles. The optimization of electrochemical conditions was achieved by systematically varying the applied voltage within the range of 1.0 to 12.0 V. Remarkably, maintaining a voltage of 4.0 V for a duration of 40 minutes at a temperature of 25°C yielded a mirror-like surface finish. Scanning electron microscopy (SEM) analysis substantiates the effective electropolishing of both nickel and cobalt surfaces. Further characterization employing atomic force microscopy (AFM) enabled quantification of surface topography for both unpolished and electropolished regions. Specifically, for nickel, the surface roughness values (Ra) exhibited a reduction from 301.2 nm to 112.0 nm after electropolishing. Similarly, cobalt surfaces demonstrated a decrease in Ra from 315.2 nm to 89.9 nm upon electropolishing, further confirming the effectiveness of the electropolishing process.