Enhanced photoelectrochemical water splitting performance of vertically aligned Bi2O3 nanosheet arrays derived from chemical bath deposition method by controlling chemical bath temperature and complexing agent concentration

Abstract

Introduction of nanotechnology to the issue of photoelectrode fabrication is promising enough to overcome the difficulties of developing photoelectrochemical water splitting. In the recent past, photoelectrodes based on two-dimensional materials, particularly those with nanosheets less than 100 nm thick, received considerable attention. In this study, the Chemical Bath Deposition (CBD) method was employed to prepare vertically aligned Bi2O3 nanosheet arrays on FTO-coated glass substarate. Experiments were carried out to determine the impact of changing the parameters of the CBD method, i.e., bath temperature and complexing agent concentration, on the physical and photoelectrochemical properties of Bi2O3 nanosheet coatings. The samples were characterized by X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), UV-visible spectroscopy, Photoluminescence spectroscopy (PL), Raman spectroscopy, Linear Sweep Voltammetry (LSV) under light-chopped illumination, and Electrochemical Impedance Spectroscopy (EIS). Experimental results demonstrated that the bath temperature was effective in the physical properties of Bi2O3 coatings so that upon increasing the bath temperature from 45 °C to 60 °C, the size of nanosheets and the thickness of coating increased and the electrochemically active surface area dramatically decreased and the bandgap of coatings changed from 2.63 eV to 2.31 eV. However, further increase in the bath temperature up to 75 °C led to a reduction of electrochemically active surface area and an increase in the size of nanosheets, in the thickness of the coating, and in the bandgap to 2.49 eV. The photoelectrode obtained from the chemical bath at a temperature of 60 °C exhibited the highest photocurrent density of 470 μA/cm2 at 1.2 VRHE, which is mainly attributed to its lowest charge transfer resistance and the narrowest bandgap. Using low concentrations of complexing agent, triethanolamine (TEA) in a chemical bath did not provide coating on a substrate. Less compact and intertwined Bi2O3 nanosheet arrays and a more crystallized and porous coating were formed with an increment in TEA. The density of photocurrents varied at the molar ratio of TEA to bismuth ion in the order of 4 > 6 > 3, which is ascribed to their physical properties, charge generation, and transfer abilities. Among the Bi2O3 nanosheet photoelectrodes, the sample that was prepared in the chemical bath at 60 °C at a TEA to bismuth ions molar ratio of 4 had the highest photocurrent density of 750 μA/cm2 at 1.2 VRHE.