Reconstitution behavior of Cu-Au bimetallic catalysts in electrocatalytic CO2 reduction reactions

On September 14, 2022, Beijing time, Professor Zhang Liming of Fudan University, in collaboration with Professor Dai Sheng of East China University of Science and Technology, and Professor Liu Kaihui of Peking University, published a research result entitled “Dynamic restructuring of epitaxial Au-Cu biphasic interface for tandem CO2-to-C2+ alcohols conversion” in the journal Chem.

This result studies the atomic-level reconstruction/phase transition of bimetallic electrocatalysts in the process of electrocatalytic carbon dioxide reduction in the model system of epitaxial Au-Cu heterostructure, and establishes a research example of the structure-activity relationship between series catalytic carbon dioxide to polycarbon alcohols from the atomic scale. The corresponding authors of the paper are Zhang Liming, Dai Sheng, Liu Kaihui; The first authors of the paper are Zhu Chenyuan, Zhou Liyi and Zhang Zhibin.

Electrochemical carbon dioxide reduction (CO2R) is expected to convert CO2 into a valuable fuel from renewable electricity energy sources to maintain carbon balance, so it is of great concern. High economic value-added multi-carbon compounds (such as ethylene, ethanol, n-propanol, etc.) occupy an important position in the chemical industry and the national economy. Among the many catalysts, the metallic copper (Cu) based compound is currently the catalyst that is mainly capable of carbon-carbon coupling to produce multi-carbon fuels. However, carbon-carbon coupling on elemental Cu surfaces often requires a higher overpotential, and in most cases the selectivity and yield are poor, hindering its practical application. The design of bimetallic tandem catalysts to regulate the binding energy of key intermediates on the surface of Cu is an effective means to improve the selectivity of multi-carbon products. In this system, the CO2R process can be divided into two continuous steps, that is, the CO2 is reduced to CO in a highly selective catalyst (such as Ag, Au, etc.), and then the carbon-carbon coupling on cu is carried out to form a multi-carbon product. So far, most of the research on Cu-based bimetals has understood the active sites and reaction mechanisms from a theoretical point of view, and there is still a lack of experimental studies of the real active sites during the CO2R reaction, especially under the premise that the metal structure dynamics are unstable.

Recently, Liming Zhang’s team at Fudan University studied the reconstruction/phase transition of bimetallic electrocatalysts in the CO2R process based on atomically resolved electron microscopy as a model system with the epitaxial Au-Cu heterostructure as a model system. More importantly, the structure-activity relationship between the real active site of the bimetal and the yield of polycarbon alcohol after the reconstruction was verified by experiments and theory, and the In situ formation of AuCu alloy and Cu nanoshell were the active sites of CO2 to CO and CO to polycarbon alcohol, respectively, and the local enrichment of *CO was the key to the stable production of polycarbon alcohol.

Figure 1: Epitaxial growth Au-Cu bimetallic heterojunction structure characterization.

Figure 2: Au-Cu bimetallic CO2R performance test.

Based on the lattice induction of single crystal copper foil, the epitaxial growth of Au nanoparticles on the surface of copper foil was realized, and a regular Au-Cu bimetallic heterostructure was obtained. HaADF-STEM characterization shows that au-Cu bimetals have phase-separating heterostructures with well-defined atomic interfaces. Electrochemical test results indicate that epitaxial Au-Cu effectively improves the yield and overpotentiality of CO2 to polycarbon alcohols and inhibits the production of hydrocarbons compared with elemental Cu. Stability tests reveal the inactivation of polycarbon alcohols on time scales.

Figure 3: Schematic diagram of the reconstruction of the atomic-level Au-Cu bimetallic interface and its reconstruction mechanism.

Quasi-in situ spherical aberration electron microscopy was used to explore the structure of Au-Cu bimetallic after CO2R reaction. The results showed that after the CO2R reaction, the Au-Cu interface of the initial phase separation was transformed into a unique AuCu alloy-supported epitaxial Au@Cu core-shell nanocluster structure. The main reason for the reconstruction of the Au-Cu interface is the redox of Cu(0) in solution and the diffusion of Au atoms, in which some Au atoms diffuse into the Cu lattice to form AnAuCu alloy, while the normal valent State Of Cu is re-deposited to form a Cu nano shell.

Figure 4: Analysis of au-Cu bimetallic active sites and their structure-activity relationship after reconstruction.

The results of in situ infrared spectroscopy and the electrochemical results described above (Figure 2) show that although the Au-Cu heterojunction has been reconfigured, its tandem catalytic effect still exists. Based on the reconstructed structure, the researchers believe that the AuCu alloy and the Cu nanoshell are the active sites of CO2 to CO and CO to polycarbon alcohol, respectively. COMSOL simulation, DFT theoretical calculation and time scale in situ infrared results confirm that the *CO local enrichment generated by the AuCu alloy site is the key to the stable production of multi-carbon alcohol. (Source: Science Network)

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