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

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 CO₂ 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 Bi₄Ti₃O₁₂, yielding tight and homologous Bi/Bi₄Ti₃O₁₂ (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 CO₂, 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 CO₂ 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 CO₂ reduction.