Switching of a type I to an all-solid-state Z-scheme heterojunction by an electron mediator rGO bridge: 18.4% solar-to-hydrogen efficiency in n-ZnS/rGO/p-Bi2S3 ternary catalyst

Abstract

• rGO as an electron transport medium bridged between n-ZnS and p-Bi 2 S 3 particles. • A faster charge carrier diffusion and a slower e − /h + recombination on ZnS/rGO/Bi 2 S 3 . • rGO bridge more effectively transported electrons than holes. • Type I band arrangement rearranged into a typical all-solid-state Z-scheme after junction with rGO electron mediator. • ZnS/rGO/Bi 2 S 3 achieved 18.4% solar-to-hydrogen efficiency. The problem of charge transport at incomplete contact interfaces within heterogeneous junction particles remains unresolved. This study experimentally demonstrates that rGO, an electron transport mediator between p- and n-type semiconductors with a Type I band arrangement, connected between the contact interfaces, promotes the diffusion of charge carriers and completely separates them. An independent assessment method is used to confirm the role of the rGO. The photoelectrocurrent coupled between the two external circuits increases the presence of rGO more significantly in n-type ‖ p-type, as compared with n-type ‖ n-type or p-type ‖ p-type, electrodes. The fabricated n-ZnS/rGO/p-Bi 2 S 3 ternary catalyst absorbs the light wavelength widely, diffuses and separates the photoinduced charge carriers rapidly and strongly, and recombines e − and h + more slowly. Additional ∙OH and ∙O 2 − radicals gather at the valence band of n-ZnS and conduction band of p-Bi 2 S 3 during water splitting, respectively. The n-ZnS/rGO/p-Bi 2 S 3 catalyst produces 2523.4 μmol g −1 h −1 H 2 under simulated solar irradiation, corresponding to an 18.4% solar-hydrogen efficiency. Furthermore, the possibility of using it as an OER electrode is confirmed. Ultimately, this study reveals that the n-ZnS/p-Bi 2 S 3 particle with a Type I band arrangement before contact is converted into a typical all-solid-state Z-scheme after the junction by bridging the rGO electron mediator. Eventually, the rearranged band diagram facilitates charge transfer, inhibits the recombination of excitons, and significantly enhances the catalytic activity.