Dual Organic‐Inorganic Encapsulation and Ternary Heterojunction Engineering Toward Water‐Resistant CsPbBr ₃ Perovskite Photocatalysts for Hydrogen Production

Metal halide perovskites are promising photocatalysts for solar hydrogen production but suffer from severe water instability. Herein, a dual organic‐inorganic encapsulation strategy is developed to construct water‐resistant CsPbBr 3 nanocrystals. Hydrophobic zwitterionic ligands, in combination with an epitaxial CsPb 2 Br 5 shell, effectively isolate the CsPbBr 3 core from water while maintaining structural integrity. To overcome the carrier‐blocking effect induced by encapsulation, hollow CoS x is introduced to form a sandwich‐like heterostructure, in which CsPbBr 3 is spatially confined between CoS x and CsPb 2 Br 5 . This architecture enables directional charge transfer via a Schottky CoS x /CsPbBr 3 interface for efficient electron extraction and a type‐II CsPbBr 3 @CsPb 2 Br 5 heterojunction for hole transport. Benefiting from the synergistic stabilization and charge‐management effects, the resulting photocatalyst achieves a hydrogen evolution rate of 5.36 mmol h −1 g −1 with an apparent quantum efficiency of 4.19% at 420 nm, while maintaining stable performance over five cycles. This work provides a general strategy for integrating multi‐layer encapsulation with carrier‐selective interfaces to realize durable and efficient perovskite photocatalysts for aqueous hydrogen evolution.