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

Abstract Perovskite nanocrystals (PNCs) are of great interest for visible‐light photocatalytic CO 2 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 CO 2 reduction performance of CsPbBr 3 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 CO 2 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.