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
Hyerim Park, Namgyu Son, Byung Hyun Park, Chunli Liu, Sang Woo Joo, Misook Kang
Abstract
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-Bi2S3 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 ∙O2− radicals gather at the valence band of n-ZnS and conduction band of p-Bi2S3 during water splitting, respectively. The n-ZnS/rGO/p-Bi2S3 catalyst produces 2523.4 μmol g−1h−1H2 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-Bi2S3 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.