The work describes the mechanism responsible for formation of Co-Ru alloys through electroreduction of aquachloro complexes of Co(II) and Ru(III) in an aqueous acidic chloride electrolyte of pH = 3. Identification of electrode reactions was performed based on voltammetric and electrogravimetric tests. Potential range for alloy deposition and current efficiency of electrolysis were determined by EQCM and voltammetric tests, respectively. UV-Vis spectrometry was used to examine electrolyte stability. The influence of concentration of various forms of Co(II) and Ru(III) complexes (Sigma[CoClx(H2O)(6-x)](2-x) (x = 0, 1, 2) (10-100 mM), Sigma[RuCly(H2O)(6-y)](3-y) (y = 3,4, 5, 6) (10 mM) as well as applied potential (from -0.5 to -0.9 V vs Ag/AgCl electrode), pH of electrolyte (1-3) and temperature range (25-70 degrees C) were examined towards composition, structure and morphology of deposited Co-Ru alloys. The performed structural analysis showed a high influence of the synthesis conditions on the structure and morphology of the obtained alloys. (C) 2015 Elsevier B.V. All rights reserved.