Highly aligned Cu2O/CuO/TiO2 core/shell nanowire arrays as photocathodes for water photoelectrolysis

Highly aligned Cu2O, Cu2O/CuO, Cu2O/CuO/TiO2 and Cu2O/TiO2 nanowires arrays on Au substrates were prepared by controlled air annealing of the electrodeposited Cu nanowires and furthered with dip coating. Photoelectrochemical investigations were carried out to determine their potential as photocathodes for water photo-reduction. The photocurrent of the Cu2O nanowires photocathode was found to be twice that of the Cu2O film, largely due to the higher surface area and the shorter carrier diffusion length associated with the nanowires array configuration. However, the bare Cu2O nanowires suffered from a significant photo-induced reductive decomposition with the electronic state of copper transferred from Cu(I) to Cu(0). By modifying the surface of the Cu2O nanowires with protecting layers of CuO and TiO2, direct contact of Cu2O with the electrolyte was avoided and the Cu2O/CuO/TiO2 coaxial nanocable structures were found to gain a 74% higher photocurrent and 4.5 times higher stability, compared with the bare Cu2O nanowires array. To understand the mechanism of the improved performance, a detailed characterization and analysis on the structure, circuitry and band alignment for the Cu2O/CuO/TiO2 configuration was carried out. The present study suggests a promising nanostructured photocathode configuration, which can lead to a large photocurrent with good stability against photocorrosion.