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 MnIn₂S₄ atomic layers to build a consecutive symmetry-breaking structure of isolated InO₁S₅ sites. More charges aggregate around O, making the isolated InO₁S₅ sites highly polarized. Due to the formation of the InO₁S₅ 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 MnIn₂S₄ to 1130 ps in amorphous Mn_<i>x</i>In₂S_<i>y</i>. Meantime, the formed large charge density gradient favors coupling and activation of small molecules. Benefiting from these features, a good NH₃ photosynthesis performance (515.8 μmol g^-1 h^-1) can be realized over amorphous Mn_<i>x</i>In₂S_<i>y</i>, roughly 2.5 and 48.9 times higher than those of MnIn₂S₄ atomic layers and bulk MnIn₂S₄, respectively. The apparent quantum yields reach 5.4 and 3.3% at 380 and 400 nm, respectively. Meanwhile, a greatly improved CO₂ reduction activity is also achieved over Mn_<i>x</i>In₂S_<i>y</i>. This strategy provides an accessible pathway for designing an asymmetrical polarization plane to motivate photocatalysis optimization.