Amorphizing MnIn₂S₄ Atomic Layers Create an Asymmetrical InO₁S₅ Polarization Plane for Photocatalytic Ammonia Synthesis and CO₂ Reduction

Building a polarization center is an effective avenue to boost charge separation and molecular activation in photocatalysis. However, a limited number of polarization centers are usually created. Here, a polarization plane based on two-dimensional (2D) atomic layers is designed to maximize the surface polarization centers. The Mn in a 2D crystal lattice is etched from the MnIn 2 S 4 atomic layers to build a consecutive symmetry-breaking structure of isolated InO 1 S 5 sites. More charges aggregate around O, making the isolated InO 1 S 5 sites highly polarized. Due to the formation of the InO 1 S 5 polarization plane, an enormous polarized electric field is formed perpendicular to the 2D atomic layers and the carrier lifetime can be prolonged from 93.2 ps in MnIn 2 S 4 to 1130 ps in amorphous Mn x In 2 S y . Meantime, the formed large charge density gradient favors coupling and activation of small molecules. Benefiting from these features, a good NH 3 photosynthesis performance (515.8 μmol g –1 h –1 ) can be realized over amorphous Mn x In 2 S y, roughly 2.5 and 48.9 times higher than those of MnIn 2 S 4 atomic layers and bulk MnIn 2 S 4, respectively. The apparent quantum yields reach 5.4 and 3.3% at 380 and 400 nm, respectively. Meanwhile, a greatly improved CO 2 reduction activity is also achieved over Mn x In 2 S y . This strategy provides an accessible pathway for designing an asymmetrical polarization plane to motivate photocatalysis optimization.