Electrochemical Transformation of Facet-Controlled BiOI into Mesoporous Bismuth Nanosheets for Selective Electrocatalytic Reduction of CO2 to Formic Acid

Mesoporous bismuth nanosheets are prepared through electrochemical transformation of (100)-facet exposed BiOI. Theoretical modeling and calculations are used to simulate the in situ morphological transformation of BiOI into Bi. Mesoporous Bi nanosheets show superior electrochemical CO2 reduction performance. A faradaic efficiency of 95.9 % at -0.77 V-RHE for the conversion of CO2 into formic acid, is achieved for the mesoporous Bi nanosheet catalyst compared with 93.8 % at -0.87 V-RHE for the smooth Bi nanosheets. Tafel analysis and DFT calculations indicate that the electrochemical CO2 reduction on mesoporous Bi nanosheets is kinetically faster with a higher resistance to H-2 generation than that on smooth Bi(001) nanosheets. The CO2-to-HCOOH pathway is preferred through formation of an *OCHO intermediate on the (012) and (001) planes of Bi. The mesoporous structure induces a more accessible interaction with CO2, which makes a predominant contribution to the enhanced performance compared with the subsequent CO2 activation on different facets of Bi.