A pulse electrodeposited amorphous tunnel layer stabilises Cu₂O for efficient photoelectrochemical water splitting under visible-light irradiation

Surface coating of a protective layer can prevent the corrosion of Cu₂O at electrode liquid junctions (ELJs) in photoelectrochemical water splitting. However, a facile methodology for the deposition of a conformal protective layer is still a challenge. Here, an ultrathin layer of amorphous ZnO is introduced on Cu₂O by pulsed electrodeposition, to construct a "sandwich" structure of a composite photoelectrode of TiO₂/ZnO/Cu₂O on an FTO substrate. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) visualises the spatial distribution of Ti, Zn, Cu, and Sn elements of the composite. Benefiting from the homogeneous coating of a ZnO layer, visible cracks in TiO₂ coating are significantly reduced, thus preventing the direct contact between the electrolyte and Cu₂O. Moreover, due to the ultrathin property of the amorphous ZnO layer, the energetic electrons from the excited Cu₂O can be injected via the ZnO layer into TiO₂, as elucidated by time-resolved photoluminescence (TRPL) results. The resulting composite photoelectrode shows enhanced photoelectrochemical activity and stability, compared to the bare Cu₂O, as well as the TiO₂/Cu₂O photoelectrode. This study offers a versatile and effective method for improving the stability and charge separation efficiency of Cu₂O, which is useful in guiding the surface coating of other nanostructured materials for solar energy conversion.