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

Achieving single-product selectivity in photocatalytic CO₂ reduction remains an enormous challenge. Although modulating a catalyst's nanoconfined environment can mitigate the co-production of CO and CH₄ in CO₂ reduction, the contribution of nanoconfined architecture to interfacial built-in electric field (BIEF) regulation for solid-gas CO₂ conversion has received limited attention. Herein, CsPbBr₃ quantum dots (QDs) are grown in situ within the ordered porosity of boron-doped mesoporous TiO₂ (BMT) for CO₂ photoreduction under simulated solar irradiation. The composite CsPbBr₃@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 CsPbBr₃-based photocatalysts under comparable conditions. The new CsPbBr₃@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 CO₂ 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 CO₂-to-CO conversion.