Rational design of a g-C3N4/Bi2S3/ZnS ternary heterojunction photoanode for improved solar water splitting

Abstract

Photoelectrochemical (PEC) water splitting is an immensely effective method for producing hydrogen. In this study, we present the fabrication of an efficient photoanode based on a g-C₃N₄/Bi₂S₃/ZnS ternary heterojunction system using the doctor blade technique in combination with the successive ionic layer adsorption and reaction (SILAR) method. This ternary heterojunction demonstrated outstanding PEC performance, exhibiting a remarkable photocurrent density of 13.48 mA cm⁻² at 1.23 V vs. RHE in an alkaline medium. The enhanced photocurrent in the presence of hole scavengers could be due to sulfite oxidation. ZnS serves the dual purpose of acting as a passivation layer to prevent direct contact between Bi₂S₃ and the electrolyte and offering an additional active energy state to enhance charge density, thus lending operational stability to the photoanode. The incident photon-to-current efficiency (IPCE) of the g-C₃N₄/Bi₂S₃/ZnS photoanode is 2.98%, which is substantially greater than 0.69% obtained with the g-C₃N₄/Bi₂S₃ system. The g-C₃N₄/Bi₂S₃/ZnS photoanode exhibited a 94.6% average faradaic efficiency and high stability for up to 5000 seconds. Furthermore, electrochemical impedance spectroscopy (EIS) and photoluminescence (PL) studies revealed efficient electron transfer at the heterojunction and thus were in accordance with the observed enhancement of the photocurrent density of the fabricated electrodes.