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 Cu ₂O 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.