Electrochemical Conversion of CO₂ into Formate Boosted by In Situ Reconstruction of Bi-MOF to Bi₂O₂CO₃ Ultrathin Nanosheets

Substantial emissions of CO 2 have presented formidable challenges for global climate dynamics. Electrochemical reduction of CO 2 to produce formic acid (HCOOH) is considered to be a promising approach for achieving carbon neutrality. Nevertheless, the development of a catalyst exhibiting both high catalytic activity and selectivity toward desired products remains an arduous task. Herein, we report the synthesis of a unique porous bismuth-based MOF (Bi-BTC) through microwave-assisted agitation. The Bi-BTC MOF has a good catalytic performance in electrochemical CO 2 RR to formate products. At −0.9 V (vs RHE) potential, the Faradaic efficiency of formate can reach 96%, and the current density of the CO 2 RR is 25 mA/cm 2 . Bi-BTC also exhibits good electrochemical stability. FE formate and current density were maintained for 24 h with almost no attenuation. It was found that Bi-BTC was reconstructed in the CO 2 RR process. The shape of nanocolumn before electrolysis is transformed into an ultrathin nanosheet. The soft and hard acid–base theory (HSAB) proves that the reason for the reconfiguration is that the hard base ions (HCO 3 – ) and the intermediate acid (Bi 3+ ) break in the Bi–O bond in Bi-MOF, resulting in the transition of the original column structure of Bi-BTC to Bi 2 O 2 CO 3 ultrathin nanosheeets. The DFT calculation shows that the restructured Bi 2 O 2 CO 3 nanosheet exposes a crystal surface structure, which is conducive to lower the activation energy barrier of the electrochemical CO 2 RR intermediate *OCHO and stabilizing the reaction intermediate. Therefore, it is more beneficial to improve the selectivity of the electrochemical CO 2 RR to formate formation. This result proves that irreversible reconfiguration of catalyst is beneficial to electrochemical CO 2 RR. In addition, coupling a Bi-BTC cathode with a stable anode (IrO 2 ) enables battery-driven high-activity CO 2 RR and an OER with good activity and efficiency.