Abstract

Cu xS (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(H 2O) 2] deposited on ITO substrate, irradiated with UV light and electrochemically reduced. Through cyclic voltammetry experiences performed in a 0.05 M Na 2B 4O 7 buffer solution containing 5 mM Na 2S, the electroformation mechanism of Cu xS phase is controlled by a first electron transfer, obtaining an initial formation of Cu(HS) ads that evolves to a Cu xS phase. Potentiostatic current transient recorded in the potential range of -0.8 V ? E ? -0.7 V showed that the nucleation and growth mechanism of the Cu xS phase obeys a two-dimensional instantaneous process with diffusional and charge-transfer contributions. AFM analysis of the deposits shows that Cu xS phase is preferentially deposited in the valleys left by ITO particles. The average size of Cu xS particles is close to 20 nm. Cyclic voltammetry results, electromotive force determination in the Cu/Cu aq 2+/Cu xS galvanic cell, EDAX, and UV analysis demonstrate that the stoichiometric factor x in Cu x is close to 2. The electro-obtained Cu xS phase was unstable and evolved to other nonstoichiometric compounds at open circuit. The processes responsible for the instability were the own oxidation of Cu xS phase and the water reduction that takes place over Cu xS and bare ITO particles. The last process was studied by electrochemical impedance spectroscopy. Photoelectrochemical measurements in the stability potential range of the Cu xS phase shows that the electro-obtained phase presents a p-type conductivity.