Goethite and Hematite Hybrid Nanosheet-Decorated YZnO NRs for Efficient Solar Water Splitting

Hybrid metal-oxide nanostructures have drawn much attention recently because of their ability to overcome the disadvantages of each individual material to achieve high-performance solar water splitting. Using anodic electrochemical deposition, hybrid polycrystalline goethite (α-FeOOH) and hematite (α-Fe2O3) nanosheets (GOE/HM NSs) were successfully synthesized on yttrium-doped ZnO nanorods (YZO NRs). The unique morphology, with GOE/HM NSs wrapped around the length of vertically aligned YZO NRs, is favorable for light harvesting, charge transfer, and charge transportation. The density and the effective surface area of NSs were optimized for achieving a fine balance between light absorption and charge transportation between the photoanode and the electrolyte. The samples showed much improved water splitting efficiency under both UV and visible-light excitation, which represents the synergistic effects of GEO/HM NSs with YZO NRs. UV–vis absorption and incident photon-to-current conversion efficiency measurements demonstrated appropriate band alignment at interfaces, in addition to the reduced band gap energy. Electrochemical impedance spectroscopy measurements showed greatly reduced charge-transfer resistance. The hybrid material achieved an increase in the water splitting ability by a factor of 4.5 from pristine ZnO NRs (0.2 mA cm–2) to GOE/HM NSs-coated YZO NRs (0.92 mA cm–2). This represents a highly competitive strategy for improving the ability of ZnO for water splitting.