Spherical spiky ZnO/Au nanostructures for efficient photoelectrochemical water splitting

Spiky zinc oxide (ZnO)/Au nanostructures with spherical shape-defined morphologies were synthesized using polydopamine as a starting template for photoelectrochemical H₂ production under visible light-emitting diode (LED) illumination. This low-temperature processing technique not only facilitated the fabrication of ideal plasmon-sensitive heterostructures, but also enhanced the electron mobility of the photoanodes, reaching 5.7 mA/cm² [at 1.0 V vs. the reversible hydrogen electrode (RHE)] under visible LED illumination (30 mW/cm²). This notable value was 28 times greater than that observed under dark conditions, primarily attributed to the close Schottky contact between the Au and ZnO spikes. The highest applied bias photon-to-current efficiency value (6.0%, at 0.81 V vs. the RHE) and good incident photon-to-current conversion efficiency, particularly in the visible region, coupled with a significant decrease in photoluminescence intensity, was achieved for the ZnO/Au photoanodes, owing to the improved light harvesting capability and effective electron-hole separation, resulting in the injection of hot electrons from Au to the conduction band of the spiky ZnO. This unique synthesis technique revealed a new generation of visible-light responsive plasmonic heterostructures with regular morphologies for efficient conversion of solar to H₂ fuels and energy storage applications.