Engineering the Stable BiO Species for Efficient Electroreduction of CO₂ into Formic Acid at Ampere-Level Current

BiO species have been identified as the most important active species for the electroreduction of CO₂ to HCOOH over Bi-based materials. However, the BiO species are unstable under high reduction current/potential, limiting further industrial application. Herein, we constructed robust BiO species by incorporating sodion (Na⁺) into Bi nanosheets (denoted as Na-Bi nanosheets). The negatively charged BiO species anchored by the stable Na⁺ in Na-Bi nanosheets displayed highly structural stability during CO₂ electroreduction. When the applied current density (j) was set from -200 to -1200 mA cm^-2, all of the faradaic efficiency (FE) of HCOO^- (FE_HCOO) for Na-Bi nanosheets was maintained over 90% in the flow-cell device, whereas the FE_HCOO for pure Bi nanosheets was dramatically decreased from 90% to 5%. Mechanistic study further revealed that the Na⁺-anchored BiO species can not only alter the potential-limiting step (PLS) but also decrease the energy barrier of the PLS for the electroreduction of CO₂ into HCOOH.