Electrosynthesis and electrochemical characterization of a thin phase of CuxS (x→2) on ITO electrode

CuxS (x --> 2) thin films were obtained by sulfidization of copper thin films previously obtained by spin-coating from a dichloromethane solution of [Cu(II)(2-ethyl hexanoate)(2)(H2O)(2)] deposited on ITO substrate, irradiated with UV light and electrochemically reduced. Through cyclic voltammetry experiences performed in a 0.05 M Na2B4O7 buffer solution containing 5 mM Na2S, the electroformation mechanism of CuxS phase is controlled by a first electron transfer, obtaining an initial formation of Cu(HS)(ads) that evolves to a CURS phase. Potentiostatic current transient recorded in the potential range of -0.8 V less than or equal to E less than or equal to -0.7 V showed that the nucleation and growth mechanism of the CuxS phase obeys a two-dimensional instantaneous process with diffusional and charge-transfer contributions. AFM analysis of the deposits shows that CuxS phase is preferentially deposited in the valleys left by ITO particles. The average size of CuxS particles is close to 20 nm. Cyclic voltammetry results, electromotive force determination in the Cu/Cu-aq(2+)/CuxS galvanic cell, EDAX, and UV analysis demonstrate that the stoichiometric factor x in CuxS is close to 2. The electro-obtained CuxS phase was unstable and evolved to other nonstoichiometric compounds at open circuit. The processes responsible for the instability were the own oxidation of CuxS phase and the water reduction that takes place over CuxS and bare ITO particles. The last process was studied by electrochemical impedance spectroscopy. Photo electrochemical measurements in the stability potential range of the CuxS phase shows that the electro-obtained phase presents a p-type conductivity.