Embedment of anodized p-type Cu₂O thin films with CuO nanowires for improvement in photoelectrochemical stability.

A highly stable p-type cuprous oxide (Cu2O) photoelectrode has been fabricated by direct anodization of the Cu foil, followed by a thermal treatment to introduce a protective layer of copper oxide (CuO) nanowires penetrating the surface of the Cu2O layer. The anodized Cu2O served as the seeding sites for the growth of CuO nanowires. The embedment of CuO nanowires within the Cu2O matrix enhanced the adhesion of the nanowires onto the Cu substrate. In addition, the presence of CuO nanowires on the outer layer of the composite film, in turn stabilized the Cu2O layer by passivating the redox activities of Cu2O when exposed to the environment. This nanostructured p-type Cu2O photoelectrode generated 360 μA cm(-2) of photocathodic current density upon visible light illumination and managed to retain its photocathodic current density after being used and kept for one month. The improvement in photoelectrochemical (PEC) stability by introducing a passive layer of CuO nanowires provides useful insights into the development of a Cu2O photoelectrode, as its stability remained as the main challenge.