In situ transformation of bismuth-containing precursors into ultrathin bismuth nanosheets for enhanced electrochemical CO2 reduction

Bismuth nanosheets (Bi NSs) are promising electrochemical carbon dioxide reduction (E-CO2RR) electrocatalysts due to their unique structure and economy. Herein, ultrathin Bi NSs with two kinds of thicknesses (1.5 nm and 3.1 nm) were synthesized from precursors Bi2MoO6 and BiOIO3, respectively by an efficient cathodic reduction process. Characterization results show that the thickness of the ultrathin Bi NSs is related to the structure of the bismuth-containing precursor under the same transformation conditions. Especially, in situ Raman spectroscopy revealed a similar structure evolution for two kinds of ultrathin Bi NSs from precursors Bi2MoO6 and BiOIO3. TEM shows that the thinner nanosheets (1.5 nm Bi NSs) are dotted with a large number of coordination-unsaturated pits, while the thicker nanosheets (3.1 nm Bi NSs) are more intact. The aberration-corrected HAADF-STEM images further reveal that thinner nanosheets can produce more edge sites. Hence, 1.5 nm Bi NSs exhibited a 94.5 % formate Faradaic efficiency (FEformate) at −0.98 V vs RHE, while 3.1 nm Bi NSs had a FEformate of 92.5 %. Notably, throughout a broad potential window of 700 mV (-0.77 to −1.47 V vs RHE), the FEformate for 1.5 nm Bi NSs was consistently above 90 % in the flow cell. These results demonstrate how the edge sites of Bi NSs are created and catalyze the E-CO2RR, which provides new insights into the development of high-performance bismuth catalysts for E-CO2RR to formate.