Enhanced Visible‐Light Photocatalytic CO ₂ Reduction of Perovskite Nanocrystals via Interfacial Acid Reaction

Perovskite nanocrystals (PNCs) are of great interest for visible-light photocatalytic CO₂ reduction because of their excellent optical and optoelectronic properties with suitable band positions. Given that such photophysical properties, as well as catalytic activity, are highly surface-dependent, PNC surfaces must be engineered to optimize all these aspects. Herein, a facile and effective method is introduced for enhancing the photocatalytic CO₂ reduction performance of CsPbBr₃ PNCs through interfacial reactions involving hydrobromic acid and oleylamine in water and hexane, respectively. The H⁺ ions supplied from the water phase protonate oleylamine to produce oleylammonium, and the supplied Br^- ions fill the halide vacancies of the PNCs in hexane, which can be stabilized by oleylammonium passivation. Consequently, this process enables proton source generation and surface defect passivation in a single step, yielding PNCs with significantly enhanced photoluminescence quantum yields and photocatalytic CO₂ reduction activity under visible-light irradiation. In situ diffuse-reflectance infrared Fourier-transform spectroscopy reveals that the enhanced photocatalytic activity arises from the reaction pathway involving oleylammonium as a proton source. This study demonstrates the potential of simple oil-water interface systems for PNC surface modification, offering a practical route to visible-light-driven energy conversion technologies.