Nanotextured cupric oxide nanofibers coated with atomic layer deposited ZnO-TiO₂ as highly efficient photocathodes

We report the fabrication and performance of a CuO/ZnO/TiO₂ nanofiber photocathode that achieved a photocurrent density (PCD) of −4.1 mA/cm², which is among the highest PCD values reported for a copper oxide based photocathode without a co-catalyst. To prepare this photocathode, we coated electrospun nanofibers with copper by electroplating, then dried them in air to produce cuprous oxide (Cu₂O) nanofibers. Further annealing in air converted them to cupric oxide (CuO). The CuO nanofibers exhibit nanotextured surfaces, resembling the skin of the “thorny-devil” lizard of Australia, providing high accessible surface area for photocatalysis. These CuO nanofibers were uniformly coated with thin ZnO and TiO₂ layers by atomic layer deposition (ALD) to promote electron migration from CuO to TiO₂ and protect the CuO from corrosion. The nanofibrous photocathode films were characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, and transmission electron microscopy, as well as by incident photon-to-electron conversion efficiency measurements.