Exsolution synthesis of ferroelectric bilayer MoS₂ in particulate systems as encapsulating chainmail cocatalysts

While two-dimensional (2D) ferroelectrics in the form of films have proven their potential in manipulating charge carrier dynamics across diverse systems, the synthesis and application of 2D ferroelectrics in particulate scenarios remain largely unexplored. Fundamental obstacles persist in achieving and maintaining stable ferroelectric ordering within nanoscale domains. Herein, we report a strategy for the controlled exsolution growth of a robust ferroelectric MoS₂ bilayer, which self-assembles into a chainmail architecture that uniformly encapsulates 80 nm CdS nanoparticles. The emergence of ferroelectricity in the MoS₂ bilayer originates from asymmetric lattice contraction, where the inner layer undergoes a compressive strain of 1.51% relative to the outer layer. This built-in polarization gradient substantially enhances the vertical (out-of-plane) migration of photoexcited electrons within the MoS₂ structure, as unambiguously evidenced by angle-resolved THz emission spectroscopy. When employed as a cocatalyst, the ferroelectric MoS₂ bilayer remarkably boosts the extraction efficiency of visible-light-generated electrons, achieving an 8.6-fold enhancement in photocatalytic hydrogen production compared to conventional non-ferroelectric analogues. This breakthrough not only advances cocatalyst design principles but also expands the functional landscape of ferroelectric materials in energy conversion technologies.