Phosphomolybdic Acid-Assisted Growth of Ultrathin Bismuth Nanosheets for Enhanced Electrocatalytic Reduction of CO₂ to Formate

Oxides containing two-dimensional metallic catalysts have shown enhanced catalytic activity, stability, and product selectivity. Porous three-dimensional structures maximize the accessibility of the active sites, thus enhancing the catalytic performance of the catalysts. By integrating these desirable features in a single catalyst, further improvement in catalytic activity and selectivity is expected. In this study, oxide-containing bismuth (Bi) nanosheets of about 4 nm thickness interconnected to form a porous three-dimensional structure were synthesized by electrodeposition in the presence of phosphomolybdic acid under hydrogen evolution conditions. These Bi nanosheets catalyze CO₂ reduction in a CO₂ -saturated 0.5 m NaHCO₃ solution to formate with a faradaic efficiency of 93±2 % at −0.86 V vs. RHE with a formate partial current density as high as 30 mA cm ⁻² . The Tafel slope of about 78 mV dec ⁻¹ suggests that the protonation of the adsorbed CO ₂ ^.− is the rate-limiting step.