Achieving current density of 815 mA/cm² for electrochemical CO₂ reduction to formate by enhancing *OCHO intermediate adsorption through intercalated Bi single atoms in BiOBr

The CO₂ electrochemical reduction reactions (CO₂ER) to produce high-value formate are crucial for closing the anthropogenic CO₂ cycle. Modulating the adsorption energy between *OCHO and Bi atoms in Bi-based catalysts could enhance both the activity and selectivity for formate formation. Here, a Bi/BiOBr nanosheet with highly dispersed Bi single atoms in intercalations was synthesized through NaBH₄ treatment of BiOBr, which retained the intercalated Bi atoms after electrolysis (Bi/BiOBr-D). The intercalated Bi atoms optimize the Bi-6p band center (0.016 eV) and charge distribution in Bi/BiOBr-D, enhancing the coupling between the O-2p orbitals of *OCHO and the Bi-6p orbitals as well as the electron transfer dynamics between Bi and the *OCHO intermediate, which improves the stability of the *OCHO intermediate during CO₂ER. Further studies demonstrate that enhanced *OCHO adsorption reduces the Gibbs free energy barrier for the CO₂→*OCHO process and suppressing the formation of the *H intermediate. Those advantages lead to high selectivity (FE of 96.83 %) in H-type cell, and excellent activity (j_HCOO- of 815 mA/cm²) and productivity (15.22 mmol/h·cm²) in flow cell for formate production over Bi/BiOBr-D sample.