Surface Epitaxial\nGrowth of 2D/2D Bi<sub>2</sub>O<sub>2</sub>S/CdS Heterojunction Photoanodes\nand Their Photoelectrochemical\nProperties

Constructing high catalytic activity heterojunctions\nto compensate\nfor the shortcomings of single catalysts has promoted the development\nof semiconductor catalysts in photoelectrochemical (PEC) water splitting.\nIn this case, the 2D/2D Bi<sub>2</sub>O<sub>2</sub>S/CdS composite\nwas successfully constructed by an in situ surface epitaxial growth\nmethod. At 1.23 V vs RHE, the catalytic activity of Bi<sub>2</sub>O<sub>2</sub>S/CdS with a 2D/2D heterojunction is the highest, and\nthe current density of the Bi<sub>2</sub>O<sub>2</sub>S/CdS photoanode\nis 3.46 mA/cm<sup>2</sup>. Compared with the Bi<sub>2</sub>O<sub>2</sub>S photoanode (0.59 mA/cm<sup>2</sup>), the performance has been improved\nby 5.86 times. In electrochemical impedance spectroscopy testing,\nthe arc radius of 2D/2D Bi<sub>2</sub>O<sub>2</sub>S/CdS is smaller\nthan that of Bi<sub>2</sub>O<sub>2</sub>S, indicating faster charge-transfer\nkinetics. The data show that the 2D/2D heterojunction with surface–surface\ncontact successfully enhances the catalytic activity of Bi<sub>2</sub>O<sub>2</sub>S, greatly elevating the efficiency of charge separation\nand migration. This study provides a method to enhance the PEC activity\nin type-I heterojunction photoelectrodes, promoting the application\nof Bi<sub>2</sub>O<sub>2</sub>S-based materials in photoelectrochemistry.