Sulfur ion-exchange strategy to obtain Bi₂S₃ nanostructures from Bi₂O₃ for better water splitting performance

A two-step simple and efficient ion-exchange chemical strategy is proposed to obtain nanostructured Bi₂S₃ electrodes of different surface morphologies from the Bi₂O₃. In the first step, nanoplates of the Bi₂O₃ are obtained on nickel-foam using successive ionic layer adsorption and reaction method at room-temperature (25 °C). In the second phase, as-obtained nanoplates of the Bi₂O₃ are transferred to the Bi₂S₃ using four autoclaves containing different sulfur precursor solutions at 120 °C for 8 h for phase change, structural conversion and surface morphological modification (i.e., walnuts, network-type, nanowires, and nanoflowers). Due to higher surface area and conductivity, lower charge transfer resistance, and reduced band gap caused by ionic and phase conversion, the Bi₂S₃ surpasses the Bi₂O₃ in hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities. The overpotential of 112-370 mV for the Bi₂S₃ network is much lower than that of the nanoplates of the Bi₂O₃ (275-543 mV), and walnuts (134-464 mV), nanowires (125-500 mV), and nanoflowers (194-520 mV) of the Bi₂S₃. The Bi₂S₃ network-type Bi₂S₃ electrode shows considerable chemical stability through cycling measurement, suggesting the importance of the present study in obtaining metal sulfides from metal oxide with better water splitting activities.