Enhanced charge carrier density of a p-n BiOCl/BiVO4 heterostructure by Ni doping for photoelectrochemical applications

Pure and doped p-n BiOCl/BiVO4 heterostructures with various Ni contents were studied for photoanode applications in photoelectrochemical cells. All materials were synthesized by the coprecipitation method. The properties of the pure and doped materials were characterized by various techniques, such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, UVvisible spectroscopy, and electrochemical impedance spectroscopy. Furthermore, density function theory calculations were employed to investigate the underlying physical mechanism of the Ni substitution. The materials were applied as the photoanode at an applied bias voltage of +1.9 V (vs. RHE) and irradiated over 4200 s under the solar light simulator. The pure p-n BiOCl/BiVO4 heterostructure showed the highest photocurrent of 1 mA/cm2. After 1% Ni doping, the photocurrent density was enhanced, and the highest photocurrent density was approximately 1.7 mA/cm2. From the theoretical calculation aspect, the role of Ni substitution into the parent p-n BiVO4 and BiOCl materials resulted in a surface state under the conduction band of both parent materials. The result was in agreement with the Mott-Schottky analysis, which showed that the charge carrier density increased as Ni atoms were added to the p-n BiOCl/BiVO4 heterostructure. Therefore, the additional state and the increase in the charge carrier density led to the improved photocatalytic activity of the Ni-doped p-n BiOCl/BiVO4 heterostructure.