One-pot hydrothermal synthesis of Ni-doped ZnIn2S4 nanostructured film photoelectrodes with enhanced photoelectrochemical performance

Nanostructured Ni-doped ZnIn2S4 films were prepared on the FTO conductive glass substrates by a one-pot hydrothermal method. The obtained films consist of nanosheets perpendicular to the FTO glass substrate, exhibiting a net-like porous microstructure. The doping of Ni into the lattice of ZnIn2S4 is revealed by the X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) characterizations. The results from the energy-dispersive spectroscopy (EDS) and X-ray photoelectron spectrometer (XPS) confirm the existence of Ni in the doped sample. The optical absorption of the Ni-doped samples is slightly stronger than that of the undoped one. Compared with the undoped sample, the Ni-doped ZnIn2S4 photoelectrodes show enhanced photocurrent response and reach a maximum at the Ni content of 2 wt%. The carrier concentration and mobility of all the samples were estimated by using Hall measurements. The carrier concentration decreases with the increase of Ni content, and 2 wt% Ni-doped ZnIn2S4 photoelectrode has the highest mobility, which is up to 840 cm2/Vs. The results from the electrochemical impedance spectroscopy (EIS) measurements indicate that the lowest charge transfer resistance is achieved by the 2 wt% Ni-doped ZnIn2S4 photoelectrode, agreeing with its best PEC performance. The photocurrent densities vs. time curves demonstrate that the stability of the 2 wt% Ni-doped ZnIn2S4 photoelectrode is better than that of the undoped one. The enhanced PEC performance along with good stability make the Ni-doped ZnIn2S4 photoelectrode show potentials in the PEC applications such as the water splitting for hydrogen production.