Nanoconfined CsPbBr ₃ in Boron‐Doped Mesoporous TiO ₂ Enables Built‐In Electric Field Modulation for Fully Selective CO ₂ ‐to‐CO Photoconversion

ABSTRACT Achieving single‐product selectivity in photocatalytic CO 2 reduction remains an enormous challenge. Although modulating a catalyst's nanoconfined environment can mitigate the co‐production of CO and CH 4 in CO 2 reduction, the contribution of nanoconfined architecture to interfacial built‐in electric field (BIEF) regulation for solid‐gas CO 2 conversion has received limited attention. Herein, CsPbBr 3 quantum dots (QDs) are grown in situ within the ordered porosity of boron‐doped mesoporous TiO 2 (BMT) for CO 2 photoreduction under simulated solar irradiation. The composite CsPbBr 3 @BMT delivers a CO production rate of 226 µmol g −1 h −1 with essentially 100% (99.9%) selectivity in a solid‐gas system, outperforming state‐of‐the‐art CsPbBr 3 ‐based photocatalysts under comparable conditions. The new CsPbBr 3 @BMT architecture integrates pore‐level stabilization of QDs, with the nanocage framework isolating and stabilizing the QDs, as evidenced by in situ XPS and TEM. The combination of boron doping and nanoconfinement is shown by theoretical calculations to enhance the BIEF between the QDs and BMT, leading to improved charge separation and suppressed hydrogen evolution. In addition, calculations reveal that nanoconfinement stabilizes the COOH intermediate in CO 2 photoreduction while weakening CO adsorption, directing the system toward CO formation and release. These results highlight nanoconfinement as an effective strategy for selective, efficient solar‐driven CO 2 ‐to‐CO conversion.