Amorphous CoO obtained by electrochemical milling (ECM) process offers high catalytic activity towards sulfurization reaction to form amorphous CoS compared to crystalline CoO. The obtained amorphous CoS resulted in high electrocatalytic performance towards the reduction of tri-iodide for dye-sensitized solar cells (DSCs). The DSCs fabricated using the amorphous CoS electrocatalysts obtained by ECM process with high applied current density as the counter electrodes display the higher efficiencies of 731% (P-CoO30) and 7.28% (N-CoO30) relative to 6.46% and 6.03% delivered by the systems based on conventional Pt and CoS counter electrodes. Electrocatalytic abilities of the different types of counter electrodes were verified through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The measurements revealed that the large active surface area of the amorphous CoS potentially offers more active sites for tri-iodide adsorption, thus significantly enhancing tri-iodide reduction activity. (C) 2016 Elsevier Ltd. All rights reserved.