In Situ Bismuth Exsolution‐Driven Controllable Bi/Bi ₄ Ti ₃ O ₁₂ Heterointerface Catalysts for Enhanced Photocatalytic CO ₂ ‐to‐HCOOH Conversion

ABSTRACT Heterointerface engineering based on built‐in electric field (BIEF) has emerged as a promising route for regulating interfacial charge transfer and the electronic structure of active sites to achieve efficient photocatalytic CO 2 reduction. However, constructing strongly coupled heterointerfaces to maximize BIEF effects remains challenging. Herein, an off‐equilibrium solvothermal strategy is employed to induce the in situ exsolution of bismuth (Bi) nanoparticles from Bi 4 Ti 3 O 12 , yielding tight and homologous Bi/Bi 4 Ti 3 O 12 (Bi/BTOVs) heterointerface catalysts. Both experimental and theoretical analyses reveal a volcano‐type relationship between the intensity of BIEF and the size of the exsolved Bi nanoparticles. Strengthened BIEF facilitates directional interfacial charge transfer and shifts the Bi p‐band center toward the Fermi level. The optimized p‐band center strengthens the adsorption and activation of CO 2 , thus lowering the formation barrier of the *OCHO intermediate. Moreover, the Bi nanoparticles also induce a localized photothermal effect, raising the reaction temperature to accelerate CO 2 reaction kinetics. As a result, the 8 Bi/BTOVs catalyst with the optimal BIEF achieves a high HCOOH yield of 4126.25 µmol·g −1 ·h −1 with near‐unity selectivity. This study provides a generalizable strategy for the rational design of BIEF‐based strongly coupled heterointerfaces, offering a transferable design principle for photocatalytic CO 2 reduction.