Influence of Nickel Concentration on the Microstructure, Optical, Electrical, and Photoelectrochemical Properties of ZnO Nanorods Synthesized by Hydrothermal Method

Pure and nickel (Ni)-doped zinc oxide (ZnO) nanorods (NRs) with varying concentrations (2%NZO, 4%NZO, 6%NZO, 8%NZO) were successfully prepared using a hydrothermal process at 140°C. X-ray diffraction (XRD) analysis revealed a hexagonal wurtzite structure with a favorable (0 0 2) orientation for pure ZnO and Ni-doped ZnO (NZO) NRs. Fourier-transform infrared (FTIR) analysis confirmed the existence of functional groups in the samples. The estimated band gap (E_g) values were found to be 3.42 eV, 3.32 eV, 3.31 eV, 3.298 eV, and 3.25 eV for doped ZnO NRs with 0%, 2%, 4%, 6%, and 8% Ni ion concentrations, respectively. Two characteristic emission peaks of the ZnO NRs were observed in photoluminescence (PL) spectra at about 390 nm and 576 nm which are referred to as near band-edge (NBE) and wide deep-level emission (DLE), respectively. The sample 6% NZO structures exhibited the highest photoelectrochemical behavior under illumination. The supreme current density (J) of ~ 85 μA/cm² in a 0.5-M NaSO₃ electrolyte demonstrated an excellent charge separation. The current–voltage (I–V) characteristics show an increase in current with increasing Ni content from 2% to 6% and a decrease with increasing dopant level to 8%, This is in accordance with the Burstein–Moss influence. The results are expected to help in the production of low-cost, simple synthesis methods and improved photoelectrodes for biosensor and solar cell applications.