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We reported that Cu octahedra modified with low-coordinated Cu nanocluster (Cu oct @Cu_NCs) as an efficient electrocatalyst for CO 2 RR to C 2 H 5 OH. Cu oct @Cu_NCs has been synthesized by a simple solution precipitation and electroreduction. In situ Raman spectra confirmed that the defect-sites-rich Cu nanoclusters can promote the adsorption of *CO and increase the *CO coverage on Cu octahedra enclosed by Cu(1 1 1), hence facilitating the formation of C 2 H 5 OH. Thus, compared to the bare Cu octahedra, the Cu oct @Cu_NCs exhibit superior C 2 H 5 OH selectivity. [Display omitted] • Cu oct @Cu_NCs, Cu octahedra modified with low-coordinated Cu nanoclusters, were prepared by solution precipitation and electroreduction methods. • The defect-sites-rich Cu nanoclusters can promote the adsorption of *CO and increase the *CO coverage on Cu octahedra enclosed by Cu(1 1 1). • Cu oct @Cu_NCs have excellent selectivity for CO 2 RR to C 2 H 5 OH, which deliverd the FEs toward C 2 H 5 OH and C2 + products as high as 48.16 % and 83.31 % at −1.17 V vs. RHE. Copper (Cu) electrocatalysts for carbon dioxide reduction reaction (CO 2 RR) have attracted much attention due to their ability to produce high value-added C 2+ products (e.g., C 2 H 4 , C 2 H 5 OH, and n-propanol). However, achieving high selectivity of Cu electrocatalysts for C 2 H 5 OH in aqueous-based electrolytes remains a significant challenge. In this paper, we report Cu octahedra modified with low-coordinated Cu nanoclusters (Cu oct @Cu_NCs) as an efficient electrocatalyst for CO 2 RR to C 2 H 5 OH. Notably, the defect-site-rich Cu nanoclusters can promote the adsorption of *CO and increase the *CO coverage on Cu octahedra enclosed by Cu(1 1 1), thus promoting CO 2 RR to C 2 H 5 OH. We achieved a high Faradaic efficiency (FE) of 48.16 % for C 2 H 5 OH, and that of the C 2+ products is 83.31 % at −1.17 V vs. RHE. This study provides a surface nanostructured route for rationalizing efficient and selective copper electrocatalysts for CO 2 RR. [ABSTRACT FROM AUTHOR]

[Display omitted] • Through the combination of S and N atoms coordination and four metal atoms (Fe, Co, Ni, Cu), 28 TM single-atom catalysts are constructed for CO 2 RR. • Fe@S 1 N 3 SAC is predicted to have the best performance in HCOOH production with the limiting potential of −0.25 V. Cu@S 3 N 1 SAC is prominent in CO, CH 3 OH and CH 4 production (limiting potentials of −0.20 V, −0.36 V and −0.36 V). • The S 3 N 1 coordination configuration has the greatest weakening effect on the inherent linear relationship between *CO and *COOH, which has a guiding role in improving the CO 2 RR activity. • The effect of solvation (water) on the activity of different products of CO 2 RR is comprehensively discussed. • This work predicts a single-atom catalyst with excellent CO 2 RR catalytic performance: Cu@S 3 N 1 , and also provides a theoretical reference for modulating CO 2 RR catalytic performance by changing the coordination environment. As the energy crisis and global warming become ever more serious, the electrochemical reduction of carbon dioxide (CO 2 RR) using single-atom catalysts (SAC) is a potential strategy to solve these problems by converting notorious CO 2 into high value-added products. The electronic structures and the catalytic activity of SAC can be adjusted through changing the coordination environment. In this paper, 28 TM@S x N y SACs (TM = Fe, Co, Ni, Cu; x + y = 4) are constructed and the CO 2 RR performances toward C1 products are exploited. The calculations based on spin-polarized density functional theory (DFT) show that Cu@S 3 N 1 has the best catalytic performance toward CO, CH 3 OH and CH 4 , with the favorable limiting potentials of −0.20 V, −0.36 V, and −0.36 V, respectively. Fe@S 1 N 3 exhibits the best catalytic activity and selectivity toward HCOOH, with the limiting potential of −0.25 V. Electronic structure analysis reveals the catalytic origin of excellent Cu@S 3 N 1 SAC toward CO product. S x N y coordination can partially weaken the scaling relationship between *COOH and *CO, especially for S 3 N 1. Furthermore, the solvation effect and the selectivity of Cu@S 3 N 1 and Fe@S 1 N 3 under the applied potential are illustrated. The results provide a theoretical reference to regulate the CO 2 RR activity using coordinated SAC. [ABSTRACT FROM AUTHOR]