Substituent Polarity-Regulated Interfacial Polarization in Bismuth Oxyhalide/Metalloporphyrin Composites for Enhanced Charge Transfer and CO ₂ Photoreduction

The reaction efficiency of photocatalytic CO2 reduction is primarily limited by sluggish charge separation and transfer, which can be effectively addressed by constructing polarized interfaces to modulate the surface charge distribution. Herein, we propose a polar-group-modulated interfacial engineering strategy to enhance charge separation and transfer for improved CO2 photoreduction. Three inorganic semiconductor/organic molecule composite photocatalysts, BO/Pp-R (R = −COOH, −OH, and −SO3H), were constructed by integrating functionalized copper porphyrins bearing carboxyl (Pp-COOH), hydroxyl (Pp-OH), and sulfonic acid (Pp-SO3H) groups into BiOBr (BO). Characterization results reveal that increasing the substituent polarity of metalloporphyrins significantly enhances the interfacial electric field intensity, charge separation efficiency, CO2 chemisorption capacity, and photocatalytic CO2 reduction performance. Among the three, BO/Pp-SO3H exhibits the highest CO production rate of 104.10 μmol g–1 h–1, representing a 45.3-fold improvement over pristine BO, attributed to the strong polarity of the sulfonic acid groups. Through comprehensive characterization using Kelvin probe force microscopy and electron paramagnetic resonance, the underlying mechanism in which the interfacial polarization-induced electric field (IEF) drives electron transfer from the BO to the Cu2+ active sites in metalloporphyrins is elucidated. This process facilitates *COOH intermediate formation while effectively suppressing carrier recombination. This work not only advances the fundamental understanding of polar substituent effects in organic–inorganic composite photocatalysts but also establishes a universal polarity-gradient engineering strategy, providing a design paradigm for multielectron reduction catalysts.