Unlocking Built‐In Polarization via Single‐Atom Nickel Engineering in Hexagonal Cavities for Efficient Photoreforming of Biomass

Rapid bulk charge recombination in crystalline semiconductors remains a critical bottleneck hindering the scalability of photocatalytic hydrogen generation. Here, we report that precise anchoring of single-atom nickel into the hexagonal cavities of crystalline Zn₃In₄S₉ activates a strong built-in polarization electric field (PEF), which dramatically enhances charge separation. The optimized Ni_0.4-Zn₃In₄S₉ shows hydrogen production and benzaldehyde (BAD) generation rates of 48.14 and 44.72 mmol g^-1 h^-1, respectively, corresponding to 22.3- and 17.4-fold enhancements over the Zn₃In₄S₉. It also exhibits a 42.9% apparent quantum yield at 420 nm and exceptional stability, maintaining over 94.2% (H₂) and 89.2% (BAD) activity after 48 h with 6.28- and 14.4-fold stability enhancement for hydrogen and BAD production, respectively. This work proposes an atomic-level design strategy for activating PEF in Zn₃In₄S₉ hexagonal cavities, enabling highly efficient photoreforming of biomass derivatives.