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.

Melon-derived carbon nitride photocatalysts are a kind of star layered materials applied in solar energy conversion. With in-plane π orbitals of the heptazine subunits and their overlap along the melon chains being the most distinctive feature, the condition of melon chains is of great importance for the atomic and energy band structures of carbon nitride photocatalysts as well as their photo-activities. In principle, fragmentized melon chains in practical carbon nitride would lead to unfavorable structure disorder both in longitudinal and vertical directions, thus inhibiting the efficient transfer for photo-induced electrons and holes, respectively. Here, with a facile regrowth approach, that is to treat carbon nitride under the atmosphere containing C/N species, the melon chains in carbon nitride were experimentally lengthened, which was reflected by the regularly fraction variation of different nitrogen species derived from X-ray photoelectron spectroscopy (XPS) analysis. The prolonged melon chains led to dramatically improved in-plane structure order and boosted transfer of photo-induced electrons and holes, which were confirmed by the spontaneous photo-deposition of oxidants and reductants. The combination of this regrowth approach with homogenously distributed nitrogen vacancies resulted in much enhanced visible-light-responsive photoactivities. Besides, control experiments using nitrogen-vacancy-free carbon nitride and different C/N-contained precursors showed the compatibility as well as the critical factors for the lengthening effects of the regrowth approach. We hope that the facile but efficient regrowth approach could be widely adopted in melon-derived carbon nitride photocatalysts used for various applications.