It is shown that thiocyanate ions (SCN) adsorbed on an electrode surface accelerate electrochemical reduction of Cu(II), resulting in the formation of CuSCN. The acceleration effect of adsorbed SCN ions was proved by electrochemical impedance analysis and X-ray analyses of the resultant deposits. Importantly, spontaneous potential oscillation was observed during the Cu(II) reduction only in the presence of SCN, further evidenced the acceleration effect of the adsorbed SCN. (C) 2012 Elsevier B. V. All rights reserved.