Identification of Halogen-Associated Active Sites on Bismuth-Based Perovskite Quantum Dots for Efficient and Selective CO₂-to-CO Photoreduction.

Abstract

All-inorganic Pb-free bismuth (Bi) halogen perovskite quantum dots (PQDs) with distinct structural and photoelectric properties provide plenty of room for selective photoreduction of CO₂. However, the efficient conversion of CO₂-to-CO with high selectivity on Bi-based PQDs driven by solar light remains unachieved, and the precise reaction path/mechanism promoted by the surface halogen-associated active sites is still poorly understood. Herein, we screen a series of nontoxic and stable Cs₃Bi₂X₉ (X = Cl, Br, I) PQDs for selective photocatalytic reduction of CO₂-to-CO at the gas-solid interface. Among all the reported pure-phase PQDs, the as-synthesized Cs₃Bi₂Br₉ PQDs exhibited the highest CO₂-to-CO conversion efficiency generating 134.76 μmol g^-1 of CO yield with 98.7% selectivity under AM 1.5G simulated solar illumination. The surface halogen-associated active sites and reaction intermediates were dynamically monitored and precisely unraveled based on <i>in situ</i> DRIFTS investigation. In combination with the DFT calculation, it was revealed that the surface Br sites allow for optimizing the coordination modes of surface-bound intermediate species and reducing the reaction energy of the rate-limiting step of COOH^- intermediate formation from ^•CO₂^-. This work presents a mechanistic insight into the halogen-involved catalytic reaction mechanism in solar fuel production.