【introduction】

One of the most attractive ways to reduce CO2 emissions and buildup is to use electricity to electrically reduce CO2 to clean energy. However, the catalyst for CO2 electroreduction requires a high overpotential, and the hydrogen evolution reaction over the kinetics of the CO2 reduction reaction results in low product efficiency and selectivity. Low-cost and low-toxic Bi-based materials have good catalytic properties in CO2 reduction reactions, but there are few reports on Bi-based materials with high selectivity and high activity for CO2 electroreduction to CO at low overpotentials. . Recently, monoatomic catalysts have attracted much attention due to their unique electronic structure and maximized atom utilization efficiency. Pyrolysis of ZIF-8 doped with metal ions is an important strategy for the preparation of metal monoatomic catalysts, but it is difficult for metal monoatomic catalysts to remain free of Zn after pyrolysis at high temperatures. Therefore, researchers are eager to prepare pure atom-dispersed metal active sites based on novel MOF and synthetic methods.

[Introduction]

Recently, Professor Zhang Jiatao from the Beijing Institute of Technology and the team of Academician Li Yadong of Tsinghua University have collaborated to design a simple and novel method to prepare CO2 electroreduction consisting of Bi single atoms (Bi SAs/NC) supported on a nitrogen-doped carbon network. Reaction catalyst. They thermally decomposed Bi-based MOF (Bi-MOF) and dicyandiamide to synthesize Bi monoatomic catalysts. They used in situ environmental transmission electron microscopy to observe not only the conversion of Bi-MOF into Bi nanoparticles, but also the atomization of Bi nanoparticles into Bi single atoms with the aid of ammonia decomposed by dicyandiamide. The Bi monoatomic catalyst exhibits an extremely high CO2 electroreduction activity by a Faraday efficiency of up to 97% and a TOF of up to 5535 h-1 at a low overpotential of 0.39 V. Further experiments and DFT results indicate that the monoatomic Bi-N4 site is the main active center for the rapid formation of CO2, a key intermediate of CO2 activation and a key intermediate of CO products. The above results were published in the internationally renowned journal J. Am. Chem. Soc. under the title "Bismuth Single Atoms Resulting from Transformation of Metal-Organic Frameworks and Their Use as Electrocatalysts for CO2 Reduction".

[Graphic introduction]

figure 1.



(a-e) Schematic diagram of the process of converting Bi-MOF into Bi monoatoms and TEM image of Bi-MOF assisted by dicyandiamide at different temperatures

figure 2.



(a) TEM image, (b) STEM image, (c) SAED image, (d, e) magnified HAADF-STEM image of Bi SAs/NC and (f) EDS elemental analysis results.

image 3.

(a) N K-edge XANES diagram of Bi SAs/NC, Bi Cs/NC and Bi NPs/NC

(b) C K-edge XANES diagram of Bi SAs/NC, Bi Cs/NC and Bi NPs/NC

(c) k3 weighted χ(k) function of the EXAFS graph

(d) EXAFS fitting of Bi SAs/NC

Figure 4.



(a-c) Bi SAs/NC, Bi Cs/NC and Bi NPs/NC (a) LSV curve, (b) CO Faraday efficiency and (c) CO current density;

(d) Comparison of TOFs between Bi SAs/NC and most of the latest catalysts for the reduction of CO2 to CO

Figure 5.

(a) Gibbs free energy for the reaction of CO2 electroreduction to CO catalyzed by different catalysts

(b) Propose the reaction path of the entire CO2 electroreduction reaction on the surface of BiN4/C

(c) Differences in the limiting potentials of CO2 electroreduction and hydrogen evolution reactions of BiN4/C, BiC4 and Bi(110)

Literature link: Bismuth Single Atoms Resulting from Transformation of Metal–Organic Frameworks and Their Use as Electrocatalysts for CO2 Reduction (J. Am. Chem. Soc., 2019, DOI: 10.1021/jacs.9b08259)