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

BiOx species have been identified as the most important active species for the electroreduction of CO2 to HCOOH over Bi-based materials. However, the BiOx species are unstable under high reduction current/potential, limiting further industrial application. Herein, we constructed robust BiOx species by incorporating sodion (Na+) into Bi nanosheets (denoted as Na-Bi nanosheets). The negatively charged BiOx 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- (FEHCOO- ) for Na-Bi nanosheets was maintained over 90% in the flow-cell device, whereas the FEHCOO- for pure Bi nanosheets was dramatically decreased from 90% to 5%. Mechanistic study further revealed that the Na+-anchored BiOx 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.