A Versatile Self‐Templating Approach for Constructing Ternary Halide Perovskite Heterojunctions to Achieve Concurrent Enhancement in Photocatalytic CO2 Reduction Activity and Stability

Abstract Metal halide perovskite (MHP)‐based photocatalysts encounter significant stability challenges in water‐containing systems, posing a major obstacle to their application in artificial photosynthesis. Herein, an innovative and universal strategy is present to create MHP‐based ternary heterojunctions based on a self‐templating method. A series of composite catalysts featuring sandwich hollow structures are constructed, with MHPs such as CsPbBr 3 , Cs 3 Bi 2 I 9 , Cs 3 Sb 2 Br 9 , and Cs 2 AgBiBr 6 serving as the intermediate layers. The unique sandwich structure effectively shields MHPs from direct water contact, allowing MHP‐based photocatalysts to exhibit exceptional stability in water‐containing photocatalytic environments for durations exceeding 200 h. Furthermore, the hollow design ensures complete contact between the reaction substrates with both the oxidation and reduction functional areas. Compared to single perovskite materials, MHP‐based ternary heterojunction photocatalysts exhibit stronger oxidation capability and improved charge separation efficiency, leading to a substantial enhancement in photocatalytic CO 2 reduction performance. Notably, the ternary heterojunction with CsPbBr 3 as the intermediate layer achieves an electron consumption rate of up to 1824 µmol g −1 h −1 for CO 2 reduction, which is far superior to other reported MHP‐based catalysts under similar conditions. This study provides a potent strategy for simultaneously enhancing the stability and activity of MHP‐based photocatalysts, paving the way for their potential applications in artificial photosynthesis.