S-scheme heterojunction based on p-type ZnMn2O4 and n-type ZnO with improved photocatalytic CO2 reduction activity

Inspired by the carbon cycle in nature, it is promising to convert CO2 into energy-dense hydrocarbon fuels via photocatalytic CO2 reduction. In the present paper, hierarchical ZnMn2O4/ZnO nanofibers were prepared as photocatalysts by electrospinning and calcination. They outperformed pristine ZnO nanofibers with about 4-fold increment in CO and CH4 yields. Except for the advantages coming from the design, such as more exposed active sites and multiple light reflections, other benefits derived from interface charge transfer are also important. To uncover this, density functional theory calculation (DFT), along with X-ray photoelectron spectroscopy (XPS) was performed. Photoluminescence (PL) and time-resolved PL spectroscopy revealed that the charge separation efficiency in the composite was significantly elevated. Step-scheme (S-scheme) charge transfer was testified in the composite. This result, for the first time, exemplifies that S-scheme charge-transfer can also be realized in heterojunction based-on p-type ZnMn2O4 and n-type ZnO. It provides a new insight into the design of other S-scheme photocatalysts, which are composed of p-type and n-type semiconductors.