A novel approach for the preparation of textured CuO thin films from electrodeposited CuCl and CuBr

We report on the electrodeposition of CuX (X = Cl, Br) thin films on fluorine-doped tin oxide (FTO) electrodes. The electrodeposited CuX thin films, for the first time, were used as intermediates to prepare CuO thin films. Calcination of the as-prepared CuX thin films at temperatures above 380 °C allowed us to produce CuO thin films, which were used in photoelectrochemical (PEC) studies. The highest recorded photocurrent density of ∼1.3 mA/cm2 at −0.55 V (vs. Ag/AgCl) in aqueous solution was obtained from the CuO sample calcined at 460 °C. Here, we showed that the photocurrent in the unprotected CuO electrode originates from corrosion, formation of Cu2O and Cu phases, and not from water-splitting process as it has been claimed in literature. In addition, the electrochemical impedance spectroscopy allowed us to obtain the flat-band potentials of the CuO films.