According to previous literature, the C-C coupling step in the CO2RR reaction is widely considered to be the core for producing C2 products, especially ethylene. Therefore, adjusting the spatial configuration of Cu to modulate the adsorption of *CO, thereby facilitating CO-CO coupling, is regarded as an effective method to promote ethylene production.The strong adsorption of *CO and the enhanced selectivity for C2+ due to low-coordination sites are particularly significant. However, under catalytic conditions (such as pH, potential, and electrolyte), most metallic copper catalysts undergo reduction and simultaneous reconstruction during the CO2RR process, leading to the rapid deactivation of originally high-activity CO2RR catalytic sites and reduced stability. Therefore, how to precisely control low coordination density, produce high-activity Cu catalysts with low coordination density, and guide the reconstruction of copper surfaces to manufacture effective Cu catalysts under CO2RR working conditions remains a challenging and difficult task.

Driven by the aforementioned challenges, the authors established the relationship between low-coordination copper and ethylene yield using DFT calculations and simulated the reconstruction process of copper catalysts using molecular dynamics (MD). Compared to adjacent Cu atoms, the reconstructed Cu atoms retained the coordination characteristics of Cu2O, thus forming low-coordination Cu catalysts. Experimentally, the authors established a direct correlation between the selectivity of CO2RR for ethylene, the number of polygonal faces, and the coordination number.The presence of low-coordination Cu enhances the adsorption of *CO and the generation of C2H4.TS-Cu has the highest number of faces, showing significant CO2RR selectivity, with a Faradaic efficiency (FE) of 72% at a current density of 800 mA cm-2 at -0.9 V. In membrane electrode assembly (MEA) batteries, this catalyst also maintained over 70% FE for 230 hours of operation at a cell voltage of 3.5 V.

Figure 1. (a) *CO adsorption changes with the coordination number (CN) of the Cu sites.

(b) Energy profile of C-C coupling on Cu sites with various CNs.

(c) Schematic illustration of Cu and Cu2O reconstruction toward various metallic Cu states during the CO2RR. The gray, red, and brown spheres represent C, O, and

Cu atoms, respectively. The black and red dotted circles denote the vacancies after Cu and O removal, respectively.

(d) Comparison of the spatial configuration of Cu atoms in Cu and Cu2O. The dotted boxes on the Cu atoms highlight the similar Cu atom configurations and crystal face relationships between Cu and Cu2O.

(e) CuxO reconstruction toward metallic Cu via oxygen removal.

(f) The correlation of the low CN ratio of Cu and Cu2O.

Figure 2. SEM images of the Cu catalysts

(a) O-Cu

(b) T-Cu

(c) S-Cu

(d) E-Cu

(d) F-Cu

(f) TS-Cu before CO2 electrolysis.

Figure 3. (a) In situ Raman spectra of TS-Cu as a function of time during the electrochemical reduction of CO2 at -0.9 V vs RHE.

(b) Ex situ soft O K-edge XANES of the TS-Cu catalyst before and after CO2 electrolysis.

(c) XANES patterns at the Cu K-edge of different Cu catalysts after CO2 electrolysis and reference materials.

(d) The variation in the Cu coordination number after CO2 electrolysis is concomitant with the modification of the polyhedron facets of Cu2O.

Figure 4. (a) FE of different products on TS-Cu at different current densities

(b) FE

(c) ECSA-normalized partial current density toward ethylene production at 800 mA cm-2 on Cu catalysts with different polyhedron facets

(d) Single oxidative scans in Ar-saturated 1.0 M KOH for different Cu catalysts.

Figure 5. (a) Schematic diagram of the MEA electrolyzer

(b) Ethylene FE and cell voltage versus current density of TS-Cu in the MEA cell. (c) Stability test of TS-Cu at a cell voltage of 3.5 V in the MEA cell

(d) The cost analysis for the generation of C2H4 from CO2 reduction with the change in current density and Faradaic efficiency.

In summary, in this study, the authors first used density functional theory (DFT) and molecular dynamics (MD) simulations to elucidate the reconstruction behavior of catalysts under electrochemical conditions and depict their reconstruction patterns. Utilizing this reconstruction behavior, the authors designed an efficient, low-coordination copper-based catalyst. The synthesized catalyst achieved a Faradaic efficiency (FE) of over 70% for ethylene production at a current density of 800 mA cm-2. This study not only deepens the understanding of the active sites involved in designing efficient carbon dioxide reduction reaction (CO2RR) catalysts but also promotes the industrial application of carbon dioxide electrolysis technology.

Material Preparation:

The whole reaction process was carried out under the protection of argon atmosphere. TS-Cu: Firstly, 176 mg CuCl2∙2H2O, 0.5 g of PVP and 80 ml H2O were added to a 150 ml two-necked flask to form a homogeneous mixture under magnetic stirring for 20 min. After that, 10 ml 2 M NaOH was added dropwise to the above solution to form a sky-blue solution. The above solution was then added drop by drop with 10ml solution contained of 1 g L-ascorbic acid, at the same time, the heat switch was activated to increase the temperature to 50 °C. A brick red precipitate is obtained after 4 h of continuous stirring. The resulting precipitate was collected by centrifugation and was washed with deionized water and ethanol for several times to remove surface active agents attached to the surface of Cu. Finally, the obtained powder was dried in a vacuum drying box at 50 °C. The dosage of PVP in the synthesis of Six-Cu, Fourteen-Cu and Eight-Cu was 0 g, 4 g and 1 g, respectively. In addition, the solvent was replaced by ethylene glycol in the synthesis of One- Cu and argon was replaced by oxygen in the synthesis of Three-Cu. The nomenclature of catalysts is determined based on the facets exposed by the catalyst. When a spherical shape is observed where only one facet is exposed, the material is designated ‘One-Cu (O-Cu)’. For catalysts with a dice-shaped morphology, it is assumed that each facet exposes half of its surface; hence, it is denoted as ‘Three-Cu (T-Cu)’. Similarly, a catalyst with a cubic shape is labeled ‘Six-Cu’, a catalyst with an octahedral structure is referred to as ‘Eight-Cu (E-Cu)’, a catalyst with fourteen facets is named ‘Fourteen-Cu (F-Cu)’, and a catalyst with twenty-six facets is named ‘twenty-six (TS-Cu)’.This article is published by Wensheng Fang, Ruihu Lu, Fu-Min Li*, Dan Wu, Kaihang Yue, Chaohui He, Yu Mao, Wei Guo, Bo You, Fei Song, Tao Yao, Ziyun Wang*, and Bao Yu Xia* in Angew. Chem. Int. Ed. The impact factor is around 16.The original link is https://doi.org/10.1002/anie.202319936

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