Highly efficient nitrogen fixation over S-scheme heterojunction photocatalysts with enhanced active hydrogen supply.

Photocatalytic N2 fixation is a promising strategy for ammonia (NH3) synthesis; however, it suffers from relatively low ammonia yield due to the difficulty in the design of photocatalysts with both high charge transfer efficiency and desirable N2 adsorption/activation capability. Herein, an S-scheme CoSx/ZnS heterojunction with dual active sites is designed as an efficient N2 fixation photocatalyst. The CoSx/ZnS heterojunction exhibits a unique pocket-like nanostructure with small ZnS nanocrystals adhered on a single-hole CoSx hollow dodecahedron. Within the heterojunction, the electronic interaction between ZnS and CoSx creates electron-deficient Zn sites with enhanced N2 chemisorption and electron-sufficient Co sites with active hydrogen supply for N2 hydrogenation, cooperatively reducing the energy barrier for N2 activation. In combination with the promoted photogenerated electron-hole separation of the S-scheme heterojunction and facilitated mass transfer by the pocket-like nanostructure, an excellent N2 fixation performance with a high NH3 yield of 1175.37 µmol g-1 h-1 is achieved. This study provides new insights into the design of heterojunction photocatalysts for N2 fixation.

Engineering an Interfacial Facet of S-Scheme Heterojunction for Improved Photocatalytic Hydrogen Evolution by Modulating the Internal Electric Field.

Constructing a step-scheme (S-scheme) heterojunction represents a promising route to overcome the drawbacks of single-component and traditional heterostructured photocatalysts by simultaneously broadening the optical response range and optimizing the redox ability of the photocatalytic system, the efficiency of which greatly lies in the separation behaviors of photogenerated charge carriers with strong redox capabilities. Herein, we demonstrate interfacial facet engineering as an effective strategy to manipulate the charge transfer and separation for substantially improving the photocatalytic activities of S-scheme heterojunctions. The facet engineering is performed with the growth of ZnIn2S4 on (010) and (001) facet-dominated BiOBr nanosheets to fabricate ZIS/BOB-(010) and ZIS/BOB-(001) S-scheme heterojunctions, respectively. It is disclosed that a larger Fermi level difference between BiOBr-(001) and ZnIn2S4 enables the formation of a stronger built-in electric field with more serious band bending in the space charge region around the interface. As a result, the directional migration and recombination of pointless photoexcited electrons in the conduction band (CB) of BiOBr and holes in the valence band (VB) of ZnIn2S4 with weak redox ability are speeded up enormously, thereby contributing to more efficient spatial separation of powerful CB electrons of ZnIn2S4 and VB holes of BiOBr for participating in overall redox reactions. Profiting from these merits, the ZIS/BOB-(001) displays a significant superiority in photocatalytic H2 evolution over ZIS/BOB-(010) and mono-component counterparts. This work provides new deep insights into the rational construction of a S-scheme photocatalyst based on an interfacial facet design from the viewpoint of internal electric field regulation.

Bridge engineering in photocatalysis and photoelectrocatalysis.

Solar driven photocatalysis and photoelectrocatalysis have emerged as promising strategies for clean, low-cost, and environmental-friendly production of renewable energy and removal of pollutants. There are three crucial steps for the photocatalytic and photoelectrochemical (PEC) processes: light absorption, charge separation and transportation, and surface catalytic reactions. While significant achievement has been made in developing multiple-component photocatalysts to optimize the three steps for improved solar-to-chemical energy conversion efficiency, it remains challenging when weak interfacial contact between components/particles hinders charge transfer, restricts electron-hole separation and lowers the structural stability of catalysts. Moreover, owing to the mismatch of energy bands, an undesirable charge transfer direction leads to an adverse consequence. To tackle these challenges, bridges are implemented to smoothen the interfacial charge transfer, improve the stability of catalysts, mediate the charge transfer directions and improve the photocatalytic/PEC performance. In this review, we present the advances in bridge engineering in photocatalytic/PEC systems. Starting with the definition and classifications of bridges, we summarize the architectures of the reported bridged photocatalysts. Then we systematically discuss the insight into the roles and fundamental mechanisms of bridges in various photocatalytic/PEC systems and their contributions to activity enhancement in various reactions. Finally, the challenges and perspectives of bridged photocatalysts are featured.