Green electropolishing of pure titanium using a choline chloride–lactic acid deep eutectic solvent

Deep eutectic solvents (DESs) have emerged as environmentally benign alternatives to conventional acid-based electrolytes for metal surface finishing. In this study, we first employed a choline chloride–lactic acid (ChCl, 1:2 molar ratio) deep eutectic solvent as a green electrolyte for electropolishing bulk metallic titanium. An electrochemical study was performed using current–voltage (I–V) and current–time (I–t) measurements to identify the optimum polishing conditions. A stable limiting-current plateau was observed, indicating a mass-transfer-controlled electropolishing regime established by the formation of a viscous interfacial layer. Under an electrochemical potential of 7.0 V for 15 min at 25 °C, a bright, mirror-like titanium surface was obtained. We characterized surface morphology using scanning electron microscopy (SEM) and atomic force microscopy (AFM). SEM images revealed the effective removal of machining marks, scratches, and surface irregularities. At the same time, AFM analysis showed a significant reduction in average surface roughness from 727.6 ± 2.4 nm to 190.4 ± 2.1 nm, representing a 73.8% decrease . The results show that the 1 ChCl: 2 Lac deep eutectic solvent is an effective, simple, and environmentally friendly electrolyte for titanium electropolishing, offering a sustainable alternative to conventional acid-based polishing systems and a considerable voltage for advanced surface-finishing applications.