WO<sub>3</sub>/α-Fe<sub>2</sub>O<sub>3</sub>/Bi<sub>2</sub>S<sub>3</sub> Ternary Photoanode for Improved Oxygen Evolution Reaction in Photoelectrochemical Water Splitting

This study presents a ternary WO₃/α-Fe₂O₃/Bi₂S₃ photoanode system suitable for photoelectrochemical water-splitting applications. WO₃/α-Fe₂O₃ heterojunction is obtained using a hydrothermal approach, while Bi₂S₃ is deposited onto WO₃/α-Fe₂O₃ via the successive ionic layer adsorption and reaction (SILAR) method. The cycle count is adjusted to determine the optimal photocatalytic photoanode. X-ray diffraction analysis confirms different morphologies and phases for the photoelectrodes: WO₃ is deposited as plates with monoclinic phases, α-Fe₂O₃ as nanorods with hexagonal phases, and Bi₂S₃ in the form of nanoparticles (NPs) with orthorhombic phases. Solar light absorption spectra indicate that ternary WO₃/α-Fe₂O₃/Bi₂S₃ photoanodes absorb a larger portion of the solar spectrum and display a large red shift in wavelength compared to binary WO₃/α-Fe₂O₃ photoanodes. Chronoamperometric and electrochemical impedance spectroscopy measurements indicate that the as-prepared WO₃/α-Fe₂O₃/Bi₂S₃ photoanode exhibits notable stability and low charge transfer resistance (R_ct) compared to binary electrodes and pristine WO₃ plates in faradaic photoelectrochemical conversion for the oxygen evolution reaction and S^-2/S² processes. Linear sweep voltammetry studies show that the WO₃/α-Fe₂O₃/Bi₂S₃ photoanode, sensitized with 8 SILAR cycles, achieves the maximum photocurrent density of 5.777 mA.cm^-2 at 1.0 V vs. RHE under 100 mW cm^-2 simulated solar irradiation.