Enhancing photoelectrochemical performance of ZnO nanorods by forming ZnO–ZnS heterostructure via ion-exchange process

At room temperature, type-II ZnO–ZnS heterostructure is formed on ZnO nanorods grown by SILAR method with the help of ion-exchange process to enhance photoelectrochemical cell (PEC) performance of ZnO. X-ray diffraction identified ZnO with wurtzite crystal phase and amorphous nature of ZnS. Scanning electron microscopy images revealed nanorods morphology of ZnO and tiny ZnS nanoparticles appear on ZnO nanorods. The x-ray photoelectron spectroscopy and energy dispersive x-ray spectroscopy measurements confirm the ZnO–ZnS heterostructure formation. The ZnO–ZnS heterostructure demonstrates optical band gap of both ZnO and ZnS. I–V characteristics, Mott–Schottky and electrochemical impedance spectroscopy analyses indicate overall improvement in the PEC performance due to ZnO–ZnS heterostructure formation. It is found that 24 h ion-exchange time shows maximum photocurrent (0.6 mA/cm²) and photoconversion efficiency (0.33%). Nyquist plot is used to get behaviour of charge transfer resistance in ZnO–ZnS heterostructure. Mott–Schottky plot is used to investigate core mechanism and properties such as flat band potential (V_FB), doping density, etc. Possible charge transfer mechanism is given to understand the enhancement in PEC performance in case ZnO–ZnS heterostructure photoanode. Type-II ZnO–ZnS heterostructure photoanode enhances the PEC performance of ZnO nanorods due to appropriate band alignments and reduction in recombination rate and charge transfer resistance.