Visible-Light-Driven Photoreduction of CO2 with H2O Vapor over Oxygen Vacancy-Rich Mn3O4–Nanocrystal/FeOOH S-Scheme Heterojunction

Constructing S-scheme heterojunctions to achieve spatial separation of oxidative and reductive centers, rapid transfer electrons, and functional interactions is a promising strategy for realizing the overall photoreaction of CO2 and H2O. Herein, a series of Mn3O4/FeOOH S-scheme photocatalysts were prepared by anchoring Mn3O4 nanocrystals onto 1D FeOOH by the solvothermal method. The difference in the Fermi level between FeOOH and Mn3O4 in the composite system and the band bending at the interface are enhanced, thereby generating a built-in internal electric field (BIEF). In situ X-ray photoelectron spectroscopy demonstrated that BIEF directs the flow of photogenerated electrons from the conductive band of FeOOH to the valence band of Mn3O4. As a result, without cocatalysts or sacrificial agents, the S-scheme Mn3O4/FeOOH heterojunction delivers a high C1 yield rate of 22.5 μmol g–1 h–1 under visible-light irradiation, which is ca. 11.3 times higher than that of the single counterpart Mn3O4. Furthermore, introducing FeOOH with oxygen vacancies can obtain an oxidative center with a high oxygen production capacity during photocatalytic water oxidation. This enhancement not only accelerates the overall reaction but also promotes the photoreduction of CO2 by H2O. The synergistic results achieved through the S-scheme heterojunction and oxygen vacancies make it possible to produce solar fuels through reaction involving the reduction of CO2 with H2O.