Bismuth Single Atoms Resulting from Transformation of Metal-Organic Frameworks and Their Use as Electrocatalysts for CO₂ Reduction

The electrocatalytic reduction reaction of CO₂ (CO₂RR) is a promising strategy to promote the global carbon balance and combat global climate change. Herein, exclusive Bi-N₄ sites on porous carbon networks can be achieved through thermal decomposition of a bismuth-based metal-organic framework (Bi-MOF) and dicyandiamide (DCD) for CO₂RR. Interestingly, in situ environmental transmission electron microscopy (ETEM) analysis not only directly shows the reduction from Bi-MOF into Bi nanoparticles (NPs) but also exhibits subsequent atomization of Bi NPs assisted by the NH₃ released from the decomposition of DCD. Our catalyst exhibits high intrinsic CO₂ reduction activity for CO conversion, with a high Faradaic efficiency (FE_CO up to 97%) and high turnover frequency of 5535 h^-1 at a low overpotential of 0.39 V versus reversible hydrogen electrode. Further experiments and density functional theory results demonstrate that the single-atom Bi-N₄ site is the dominating active center simultaneously for CO₂ activation and the rapid formation of key intermediate COOH∗ with a low free energy barrier.