The electrocatalytic reduction of CO₂ to HCOOH (ERC-HCOOH) is one of the most feasible ways to alleviate energy crisis and solve environmental problems. Nevertheless, it remains a challenge for ERC-HCOOH to maintain excellent activity and selectivity in a wide potential window. Herein, ultra-thin flower-like Bi₂O₂CO₃ nanosheets (NSs) with abundant Bi-O structures were in situ synthesized on carbon paper via topological transformation and post-processing. Faraday efficiency of HCOOH (FE_HCOOH) reached 90% in a wide potential window (−1.5 to −1.8 V vs. Ag/AgCl). Significantly, excellent FE_HCOOH (90%) and current density (47 mA·cm⁻²) were achieved at −1.8 V vs. Ag/AgCl. The X-ray absorption fine structure (XAFS) combined with density functional theory (DFT) calculation demonstrated that the excellent performance of Bi₂O₂CO₃ NS was attributed to the abundant Bi-O structures, which was conducive to enhancing the adsorption of CO₂* and OCHO* intermediates and can effectively inhibit hydrogen evolution. The excellent performance of Bi₂O₂CO₃ NS over a wide potential window could provide new insights for the efficient electrocatalytic conversion of CO₂.