Oxygen coordinated Cu single atom catalysts: a superior catalyst towards electrochemical CO2 reduction for methane production
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Abstract
Single atom catalyst (SAC) show significant promise in electrocatalytic carbon dioxide reduction reaction
Keywords
INTRODUCTION
Electrocatalytic carbon dioxide reduction (eCO2RR) can produce valuable chemicals and fuels[1], such as carbon monoxide, methane, formic acid, methanol, ethylene, ethanol, etc.[2-7], and represents one of the most promising ways to achieve a carbon neutral cycle[8,9]. Among the many valuable products, methane (CH4), with an energy density of 55.5 MJ kg-1, is attractive for a wide range of energy applications. Efficient conversion of CO2 to CH4 not only addresses environmental concerns but also provides a sustainable energy resource compatible with existing natural gas infrastructure.
Single atom catalyst (SAC), featured by maximum atom utilization, well-defined active sites, and unique electronic and geometrical structures, have been widely studied as eCO2RR catalysts[10-13]. Previous studies have demonstrated that the coordination environment around the Cu atoms plays a crucial role in determining the activity and selectivity of SAC. For instance, Cu SAC coordinated with carbon atoms
Moreover, heteroatom doping in the coordination shells of SAC provides an effective strategy to precisely regulate their electronic structure and catalytic activity[16,17]. It is reported that Cu SAC coordinated with two N-atom (Cu-N2) in the first shell shows impressive catalytic activity in eCO2RR towards formation of ethanol[18]. However, O coordination results in lower charge density of metal center due to the higher electron negativity than N, and O-heteroatom doping into the N-coordination may induce apparent regulation towards electronic structure of metal center and the N, O co-coordinated Cu SAC (Cu-N2O2) exhibits remarkably high activity and selectivity of methane production[19]. Doping of coordination with other nonmetal elements with higher electronegativity than nitrogen equally promotes eCO2RR towards methane production. For instance, B-doping into the Cu-N coordination in the first shell of Cu SAC
Despite the promising performance of SAC, the green synthesis of these catalysts remains a critical task. The methods for synthesis of SAC have evolved from traditional techniques such as impregnation,
Herein, Cu SAC with coordination of four O atoms (Cu-O4) were prepared by three sequential steps: soaking of XC-72 in aqua regia to create defects and oxygenated functional groups, growth of copper cubes on treated XC-72 at 120 °C, soaking of the sample in acetic acid for dissolution of Cu atoms from Cu cube and deposition Cu single atoms on defects of oxygenated functional groups on carbon substrate. The unique coordination environment and spread of Cu single atoms were evidenced by high-resolution transmission electron microscopy (HR-TEM) and extended X-ray absorption fine structure (EXAFS). Cu-O4 SAC, as eCO2RR catalyst on a gas diffusion electrode (GDE) and flow cell setup, demonstrate an FE of 63.0% and a current density of 200.5 mA cm-2. Density functional theory (DFT) calculation indicates that methane production is more favored energetically than that on Cu-N4 SAC and the Cu(111) of copper nanoparticles (CuNPs), which is attributed to the optimized electronic structure and preferred adsorption of the reaction intermediates of methane on Cu-O4 SAC.
MATERIALS AND METHODS
Chemicals
Copper (II) chloride (CuCl2·2H2O), absolute ethanol (C2H5OH, 99%), glucose (99%), toner (XC-72), acetic acid (97%) were purchased from Damao Chemical Reagent. Hexadecylamine (HAD, 97%) was purchased from Energy Chemical (China). CO2 (99.995%), Ar (purity 99.99%), N2 (purity, 99.99%) and H2 (purity 99.99%) were purchased from Messer Gas (Guangzhou, China). All chemicals were used without any further purification and all solutions were prepared using deionized (DI) water (18.2 MΩ cm).
Materials synthesis
Pretreatments of XC-72
First, 10 g of XC-72 carbon material was added to a mixture of 225 mL concentrated hydrochloric acid and 75 mL concentrated nitric acid. After oxidizing for a specified duration, the resulting slurry was cooled, centrifuged, and repeatedly washed with water and ethanol until the pH reached neutral. The sample was then dried overnight at 60 °C in a vacuum oven.
Synthesis of Cu/C
XC-72 supported Cu cube (Cu/C) was synthesized according to a slightly modified version of a previously reported method[26]. In general, CuCl2-2H2O and glucose were dissolved in 80 mL of water, and after complete dissolution, XC-72 toner was added by magnetically stirring at room temperature for 5 h. HAD (1.44 g) was slowly added during this process. After forming a light blue emulsion, it was poured into the Teflon-lined chamber and heated at 120 °C for 2 h under vigorous magnetic stirring. As the reaction proceeded, the solution changed its color from blue to brown and finally red-brown. After cooling to room temperature, the samples were washed several times with DI water and ethanol to obtain the Cu/C catalyst.
Synthesis of Cu SAC
First, 70 mg of Cu/C was dispersed in a solution of acetic acid and ethanol in a volume ratio of 1:1 to remove the excess HAD organic ligand and form Cu SAC on XC-72 by acid etching. Cu SAC was obtained by centrifugation and washing several times with DI water and ethanol, and then drying for 12 h at 60 °C.
Electrode preparation
The carbon paper was cut into sheets (2.5 × 1 cm2). The catalyst was dispersed in a solution of water isopropyl alcohol and Nafion (Vwater: V isopropyl alcohol: VNafion = 1:1:0.025) to form a catalyst ink (7.5 mg mL-1) by ultrasonication for one hour. The uniformly dispersed catalyst droplets were coated on a piece of the carbon paper (Sigracet 29 BC from Fuel Cell Store) with a microporous acetylene black gas diffusion layer (GDL) on the other side (2 × 0.5 cm2 for geometric electrode surface area). The catalyst loading on the carbon paper is at 1.0 mg cm-2.
Electrochemical test
Electrochemical measurements were conducted using the CHI 760D Electrochemical Station (Chenhua Shanghai, China). CO2 electrochemical reduction experiments were performed in a custom-designed flow cell with a Pt sheet as the anode and the catalyst-coated carbon paper as the cathode, separated by an anion exchange membrane (Selemion, 2 × 1.5 cm2). Hg/HgO electrodes served as reference electrodes. All applied potentials were referenced to the reversible hydrogen electrode (RHE) based on
During electrochemical measurement, CO2 was purged into the GDL at a flow rate of 24 mL min-1 while electrolyte (1 M Ar-saturated KOH) was delivered to the flow cell at 120 rpm using a peristaltic pump. Electrochemical impedance spectroscopy (EIS) tests were carried out at an applied potential of -0.9V (RHE), a voltage amplitude of 5 mV and a frequency range (0.1 Hz to 100 kHz).
The electrochemical surface area (ECSA) of the catalysts was determined using electrochemical double layer capacitance (Cdl), as given in
where Cdl is the double layer capacitance, S is the geometric area of the working electrode (1 cm2), and Cs is the specific capacitance of the carbon-based support (0.020 mF cm-2).
The FE for the products was calculated using
where Qt (C) is the total charge collected at the applied potential, Qi (C) represents the total charge to produce the certain product, n is the number of electrons transferred for the product, which is 2 for both CO and H2, and 8 for CH4, 12 for C2H4, Ni is the number of moles of the certain product, and F stands for Faraday's constant, which has a value of 96,485 C mol-1.
Characterization
Using the JEOL ARM200F instrument (JEOL, Tokyo, Japan), the dispersion state of copper species was characterized by aberration-correction high-angle-annular-dark-field scanning transmission electron microscopy
Synchrotron radiation-based X-ray absorption spectroscopy
The X-ray absorption fine structure (XAFS) spectrum of Cu K-edge (8,979 eV) was obtained using a fluorescence mode on the BL14W1 beamline at the Synchrotron Radiation Facility (SSRF) in Shanghai, China. The storage ring of the device operates at a beam current of 3.5 GeV and 230 mA. The beamline beam was monochromatized using a double-crystal monochromator (DCM) equipped with Si (111) crystals. All XAFS spectra were analyzed using the Demeter software package (University of Chicago).
Normalization of X-ray absorption near edge structure raw data
First, the photon energy was calibrated by referencing the Cu 4f peak of a newly sputtered Cu wafer, ensuring accurate energy measurement by XAFS. Subsequently, the front edge of the Cu K-edge spectrum was set to zero using substrate lines to establish a consistent baseline reference for further analysis. Finally, the spectrum was normalized to achieve an edge-jump of one. In the fitting process, the theoretical
Computational details
All DFT calculations in this paper have been performed using the pseudopotential plane wave
where Eadsorbate+substrate, Eadsorbate, and Esubstrate are the total energies optimized for adsorbent + substrate, substrate alone, and gas-phase adsorbent, respectively.
The Gibbs free energy (ΔG) of the reaction was calculated using[31]
ΔG, ΔZPE, and ΔS denote the Gibbs free energy, the zero point energy, and the entropy, respectively.
The formation energy (Ef) serves as a metric to unveil the thermodynamic stability of all catalysts, computed as follows[32]:
nC and nO represent the quantities of C and O atoms introduced or extracted during substrate formation, μC, μO, and μCu represent the chemical potentials of C, O, and Cu elements, respectively. The values of μC, μO, and μCu are one in sixteen the energies of 4 × 4 perfect graphene, half energy of the O2 molecules in the gaseous phase, and isolated Cu single atoms, respectively.
The limiting potential (UL) represents the minimum applied potential necessary to ensure each elementary step in the proposed mechanism is exergonic. UL can be determined using[33]
where ΔGMAX denotes the free-energy change for the potential determining step along each eCO2RR pathway.
RESULTS AND DISCUSSION
The Cu SAC was synthesized through acid leaching of Cu nanocrystals, as depicted in Figure 1A. Initially, Cu nanocrystals were uniformly prepared onto the carbon substrate (Cu/C) via a hydrothermal method[26,34]. Subsequently, the Cu/C catalysts were immersed in a mixed solution of ethanol-acetate
Figure 1. (A) Schematic illustration of the synthesis of the Cu SAC; SEM image of (B) Cu/C and (C) Cu SAC; (D) HR-TEM and (E) AC-HAADF-STEM image of Cu SAC; (F) HAADF-STEM, and (G) element mapping image of Cu SAC. SAC: Single atom catalyst; SEM: scanning electron microscopy; AC-HAADF-STEM: aberration-correction high-angle-annular-dark-field scanning transmission electron microscopy; HR-TEM: high-resolution transmission electron microscopy.
As shown in Figure 1B, scanning electron microscopy (SEM) images of Cu/C exhibit a majority of Cu nanocrystals and minority of Cu nanowires, which was completely dissolved by acetic acid leaching, as evidence by SEM and transmission electron microscopy (TEM) image [Figure 1C and D]. An
The powder XRD of Cu/C reveals three diffraction peaks of Cu (111), Cu (200), and Cu (220)
A comprehensive analysis of the XPS spectra for the elements Cu, C, and O was conducted to probe the bonding and chemical states of these elements in both the Cu SAC and Cu/C. Figure 2A depicts the Cu 2p XPS spectra of Cu/C and Cu SAC. Specifically, the two red dashed lines at 932.2 eV and 952.0 eV are associated with the binding energy of 2p3/2 and 2p1/2 of Cu+/Cu0, while the black dashed lines at 935.2 eV and 954.7 eV correspond to 2p3/2 and 2p1/2 of Cu2+[37], indicating that Cu/C is dominated by metallic states with a slight degree of oxidation. However, the binding energy of Cu SAC Cu2p1/2 and Cu2p3/2 was positively shifted to 952.6 eV and 932.7 eV, which are positioned between Cu2+ and Cu0, suggesting a charge state of Cu+δ between 0 and 2+ upon coordination with O atoms.
Figure 2. XPS spectra of (A) Cu 2p; (B) O 1s for Cu SAC; (C) Normalized Cu K-edge XANES spectra; (D) FT-EXAFS spectra of Cu SAC; (E) EXAFS fitting and (inset) optimized model for Cu SAC; (F) Formation energy of Cu-NxO4-x (x=0-4) configurations with the coordination number of first-shell N/O species from DFT calculations. Color scheme: C atoms are grey, O atoms are red, N atoms are blue, and Cu atoms are orange. XPS: X-ray photoelectron spectroscopy; SAC: single atom catalyst; XANES: X-ray absorption near edge structure; EXAFS: extended X-ray absorption fine structure; DFT: density functional theory; FT-EXAFS: fourier transforms of extended X-ray absorption fine structure.
The C 1s XPS of Cu/C displays C-O (286.2 eV), C=C (284.8 eV) and C-C (285.5 eV)[37-39] and an extra subtle peak emerges at 288.8 eV for Cu SAC [Supplementary Figure 2], which are indexed to the COOH of acetate functionalization on Cu SAC due to acetate acid treatment. Likewise, the O 1s XPS spectrum of Cu SAC in Figure 2B displays peaks of O-Cu (531 eV), O=C (532 eV), and O-C (533 eV) bonds[40], with a slight additional O-Cu peak compared to the Cu/C catalyst [Supplementary Figure 3]. This suggests potential bonding between Cu and O in Cu SAC.
The investigation into the electronic structure and coordination of Cu species within the catalyst involves
In the EXAFS spectra [Figure 2D], the Cu SAC exhibits a peak at 1.5 Å, similar to those observed in CuPc and CuO, indicating the possible Cu-N/O coordination. No apparent Cu-Cu coordination for Cu SAC at 2.2 Å demonstrates the atomic dispersion of the Cu atoms, consistent with the results observed by
The activity and selectivity of eCO2RR on Cu-O4 SAC and Cu/C catalysts were evaluated in a flow cell setup with a GDE and 1 M KOH electrolyte, covering the potential range from -0.7 to -1.1 V vs. RHE. The
Figure 3. eCO2RR performance: partial current density on (A) Cu-O4 SAC and (B) Cu/C at varying applied potentials; FE of various eCO2RR products on (C) Cu-O4 SAC and (D) Cu/C; (E) Stability test of Cu-O4 SAC at -1.0 V; (F) Comparison of performance indexes of eCO2RR to CH4 with reported catalysts. eCO2RR: Electrocatalytic carbon dioxide reduction; SAC: single atom catalyst; FE: faradaic efficiency; CH4: methane.
The prevailing understanding posits that the formation of C2H4 entails a C-C coupling process facilitated by adjacent Cu atoms on the crystal surfaces, a mechanism often referred to as the Langmuir-Hinshelwood (LH) mechanism[45]. Within this framework, SAC demonstrate a unique ability to suppress the C-C coupling reactions of multi-carbon (C2+) products due to their singular adsorption sites, thereby enhancing selectivity towards C1 products[46,47]. Notably, Cu-O4 SAC catalyst [Figure 3E] remains stable in ten hours of eCO2RR at -1.0 V vs. RHE, with FE over 50% and a partial current density of approximately 150 mA cm-2 for methane production. Cu SAC show exceptional catalytic performance for CO2-to-CH4 electroreduction as compared to those reported in the literature [Figure 3F, Supplementary Table 2].
The charge transfer characteristics of the catalyst were studied by Nyquist analysis. Typically, electrochemical processes at the electrode surface are controlled by interfacial charge transfer and diffusion processes on planar electrodes. The semi-circle in the high-frequency region of the Nyquist diagram usually reflects the interfacial charge transfer resistance[48]. As shown in Supplementary Figure 4, the interfacial charge transfer (Rct) of Cu-O4 SAC catalyst is almost half that of Cu/C, indicating a much faster eCO2RR process on Cu-O4 SAC.
In order to further study the intrinsic activity of the catalyst, the ECSA of the catalyst was determined by using double-layer capacitance (Cdl) [Supplementary Figure 5]. As shown in Supplementary Table 3, the ECSA of Cu-O4 SAC is 0.24 cm2, which is significantly smaller than that of Cu/C (0.64 cm2). Such reduction of the surface area of Cu-O4 SAC is mainly due to the dissolution of the Cu nanoparticles after acid leaching. When normalized to ECSA, the partial current of CH4 at each potential of Cu-O4 SAC is much higher than that of Cu/C [Supplementary Figure 6] in the potential range of -0.7V to -1.1 V (vs. RHE), indicating its high intrinsic activity towards eCO2RR for methane production.
Fully elucidating the superior activity and selectivity of Cu-O4 towards methane production, DFT calculations were employed to investigate the energetics of the eCO2RR reaction pathway[49-51]. The adsorption configurations of the eCO2RR intermediates on Cu-N4 and Cu-O4 SAC
Figure 4. Evaluation of catalytic activity by DFT simulations. (A) Free energy diagram of eCO2RR pathway to CH4; Bader charge of (B) Cu-O4 and (C) Cu-N4 SAC; (D) ΔGH on Cu-O4 SAC, Cu (111), Cu-N4 SAC; (E) Limiting potentials of CH4, CO, CH3OH and HCOOH on Cu-O4 SAC. DFT: Density functional theory; eCO2RR: Electrocatalytic carbon dioxide reduction; CH4: Methane; SAC: single atom catalyst.
The Bader charge was further calculated to gain deeper insight into the variation of the electronic structure induced by O-coordination and potential interaction on the adsorption of eCO2RR intermediates[52]. As shown in Figure 4B and C, Supplementary Figure 10, the Bader charge analysis reveals that as the number of coordinating oxygen atoms increases, the positive charge on Cu gradually decreases from +1.43 for CuN4 SAC to +1.15 for Cu-O4 SAC, indicating enhanced charge delocalization in Cu-O4 SAC than Cu-N4 SAC structure. This might be responsible for the further dynamic partial cleavage of the Cu-O bonds in Cu-O4 SAC upon adsorption of eCO2RR intermediates. The differential charge density of Cu in Cu-O4 SAC indicates less positive charge than that of Cu in Cu-N4 SAC structure [Supplementary Figure 11]. The less positive valence state of Cu in Cu-O4 SAC than Cu-N4 SAC aligns with observations from XPS and EXAFS. Similar results were observed for Cu-O4 and Cu-N4 with adsorbed *COOH and *CHO intermediates
eCO2RR to CH4 involves complex proton-coupled electron transfer (PCET)[53]. The abundant supply of *H improves eCO2RR performance[54]. The Gibbs free energy of hydrogen (ΔGH) on Cu-O4 SAC is -1.01 eV, which is 0.55 eV on Cu (111) and 1.60 eV on Cu-N4 SAC [Figure 4D]. The more negative ΔGH on Cu-O4 SAC signifies effortless H adsorption and effective inhibition of HER[54].
To evaluate the selectivity of methane by eCO2RR on Cu-O4 SAC, the energetics of other products such as CO, HCOOH and CH3OH were calculated [Supplementary Figures 15-18] based on which the UL was derived. Specifically, the limiting potential (UL) of CH4 (-0.55 V) is much lower than that of CO (-2.01 V), CH3OH (-3.21 V), HCOOH (-4.07 V) [Figure 4E], indicative of its high selectivity towards CH4. These discernible differences in UL underscore the significance of catalyst design in achieving the desired selectivity in electrocatalytic reactions. The outstanding activity and selectivity for methane formation on Cu-O4 SAC, as revealed in DFT calculations, corroborates the electrochemical results.
CONCLUSIONS
In summary, Cu SAC coordinated by four oxygen atoms were prepared by soaking Cu nanocubes on carbon support in acetic acid solution at 60 °C for 12 h. The dissolved Cu atoms from Cu cube were then captured by the oxygenated functional groups of the carbon substrate created during aqua regia treatment. The coordination structure was revealed by the EXAFS spectrum and XPS. Cu-O4 SAC demonstrates an FE of 63.0% and partial current density of 200.5 mA cm-2 towards methane production in eCO2RR. Theoretical calculation indicates that the coordination structure of Cu-O4 sites favors the strong hydrogen adsorption and hydrogenation of eCO2RR intermediates for methane production relative to that on Cu foil and Cu-N4 SAC sites. The limiting potential calculation indicates that methane is energetically favored on Cu-O4 sites compared to CO, methanol and formate. This study highlights the importance of regulating the coordination environment of SAC to steer the selectivity of eCO2RR. The low-temperature synthesis method developed herein provides a practical and scalable approach for the preparation of structure-controlled SAC, advancing the design of efficient catalysts for sustainable energy applications.
DECLARATIONS
Acknowledgments
We appreciate the Shanghai Synchrotron Radiation Facility (SSRF) for help in XAS characterization.
Authors’ contributions
Writing - conceptualization, investigation, data curation, original draft: Qin, J.
Data curation, investigation, methodology, original draft: Hu, X.
Methodology, investigation, data curation: Miao, K.
Conceptualization, data curation, investigation, writing - review and editing, supervision, funding acquisition: Kang, X.
Availability of data and materials
The raw data supporting the findings of this study are available within this Article and its Supplementary Materials. Further data is available from the corresponding authors upon reasonable request.
Financial support and sponsorship
This work was supported by the National Natural Science Foundation of China (No. 22272059).
Conflicts of interest
All authors declared that there are no conflicts of interest.
Ethical approval and consent to participate
Not applicable.
Consent for publication
Not applicable.
Copyright
© The Author(s) 2025.
Supplementary Materials
REFERENCES
1. Liu, R. X.; Peng, L. W.; He, R. N.; Li, L. L.; Qiao, L. J. A high-performance continuous-flow MEA reactor for electroreduction CO2 to formate. J. Electrochem. 2022, 28, 2104231.
2. Zhuang, T.; Liang, Z.; Seifitokaldani, A.; et al. Steering post-C-C coupling selectivity enables high efficiency electroreduction of carbon dioxide to multi-carbon alcohols. Nat. Catal. 2018, 1, 421-8.
3. Gu, Y.; Yang, J.; Wang, D. Electrochemical features of carbon prepared by molten salt electro-reduction of CO2. Acta. Phys-Chim. Sin. 2019, 35, 208-14.
4. Xiang, D.; Li, K.; Li, M.; et al. Theory-guided synthesis of heterostructured Cu@Cu0.4W0.6 catalyst towards superior electrochemical reduction of CO2 to C2 products. Mater. Today. Phys. 2023, 33, 101045.
5. Wen, J.; Wan, Z.; Hu, X.; Huang, J.; Kang, X. Restructuring of copper catalysts by potential cycling and enhanced two-carbon production for electroreduction of carbon dioxide. J. CO2. Util. 2022, 56, 101846.
6. Wan, Z. X.; Kuchkaev, A.; Yakhvarov, D.; Kang, X. W. Monodispersed Cu-TCPP/Cu2O hybrid microspheres: a superior cascade electrocatalyst towards CO2 reduction to C2 products. J. Electrochem. 2023. DOI: 10.13208/j.electrochem.2303271.
7. Zhang, H.; Wang, X.; Chen, C.; et al. Selective CO2-to-formic acid electrochemical conversion by modulating electronic environment of copper phthalocyanine with defective graphene. Chin. J. Struct. Chem. 2023, 42, 100089.
8. Birdja, Y. Y.; Pérez-gallent, E.; Figueiredo, M. C.; Göttle, A. J.; Calle-vallejo, F.; Koper, M. T. M. Advances and challenges in understanding the electrocatalytic conversion of carbon dioxide to fuels. Nat. Energy. 2019, 4, 732-45.
9. Liu, M.; Peng, M.; Dong, B.; Teng, Y.; Feng, L.; et al. Explicating the role of metal centers in porphyrin-based MOFs of PCN-222(M) for electrochemical reduction of CO2. Chine. J. Struct. Chem. 2022, 41, 2207046-52.
10. Wang, Y.; Su, H.; He, Y.; et al. Advanced electrocatalysts with sngle-metal-atom active sites. Chem. Rev. 2020, 120, 12217-314.
11. Miao, K.; Qin, J.; Yang, J.; Kang, X. Synergy of Ni nanoclusters and single atom site: size effect on the performance of electrochemical CO2 reduction reaction and rechargeable Zn-CO2 batteries. Adv. Funct. Mater. 2024, 34, 2316824.
12. Qin, J.; Han, B.; Liu, X.; Dai, W.; Wang, Y.; et al. An enzyme-mimic single Fe-N3 atom catalyst for the oxidative synthesis of nitriles via C-C bond cleavage strategy. Sci. Adv. 2022, 8, eadd1267.
13. Fu, H.; Tian, J.; Zhang, Q.; et al. Single-atom modified graphene cocatalyst for enhanced photocatalytic CO2 reduction on halide perovskite. Chin. J. Catal. 2024, 64, 143-51.
14. Shi, G.; Xie, Y.; Du, L.; et al. Constructing Cu-C bonds in a graphdiyne-regulated Cu single-atom electrocatalyst for CO2 reduction to CH4. Angew. Chem. Int. Ed. Engl. 2022, 61, e202203569.
15. Guan, A.; Chen, Z.; Quan, Y.; et al. Boosting CO2 electroreduction to CH4 via tuning neighboring single-copper sites. ACS. Energy. Lett. 2020, 5, 1044-53.
16. Deng, Y.; Zhao, J.; Wang, S.; et al. Operando spectroscopic analysis of axial oxygen-coordinated single-Sn-atom sites for electrochemical CO2 reduction. J. Am. Chem. Soc. 2023, 145, 7242-51.
17. Wang, J.; Zhang, K.; Nga, T. T. T.; et al. Chalcogen heteroatoms doped nickel-nitrogen-carbon single-atom catalysts with asymmetric coordination for efficient electrochemical CO2 reduction. Chin. J. Catal. 2024, 64, 54-65.
18. Purbia, R.; Choi, S. Y.; Woo, C. H.; et al. Highly selective and low-overpotential electrocatalytic CO2 reduction to ethanol by Cu-single atoms decorated N-doped carbon dots. Appl. Catal. B:. Environ. 2024, 345, 123694.
19. Cai, Y.; Fu, J.; Zhou, Y.; et al. Insights on forming N,O-coordinated Cu single-atom catalysts for electrochemical reduction CO2 to methane. Nat. Commun. 2021, 12, 586.
20. Dai, Y.; Li, H.; Wang, C.; et al. Manipulating local coordination of copper single atom catalyst enables efficient CO2-to-CH4 conversion. Nat. Commun. 2023, 14, 3382.
21. Yan, H.; Cheng, H.; Yi, H.; et al. Single-atom Pd1/graphene catalyst achieved by atomic layer deposition: remarkable performance in selective hydrogenation of 1,3-butadiene. J. Am. Chem. Soc. 2015, 137, 10484-7.
22. Hossain, M. D.; Huang, Y.; Yu, T. H.; Goddard, W. A. I. I. I.; Luo, Z. Reaction mechanism and kinetics for CO2 reduction on nickel single atom catalysts from quantum mechanics. Nat. Commun. 2020, 11, 2256.
23. Liu, P.; Zhao, Y.; Qin, R.; Mo, S.; Chen, G.; et al. Photochemical route for synthesizing atomically dispersed palladium catalysts. Science 2016, 352, 797-800.
24. Hu, R.; Li, Y.; Zeng, Q.; Shang, J. Role of active sites in N-coordinated Fe-Co dual-metal doped graphene for oxygen reduction and evolution reactions: a theoretical insight. Appl. Surf. Sci. 2020, 525, 146588.
25. Fauzi, A.; Chen, X.; Zhao, H.; et al. Recent progress of M-N-C single atom electrocatalysts for carbon dioxide reduction reaction. Next. Energy. 2023, 1, 100045.
26. Jin, M.; He, G.; Zhang, H.; Zeng, J.; Xie, Z.; Xia, Y. Shape-controlled synthesis of copper nanocrystals in an aqueous solution with glucose as a reducing agent and hexadecylamine as a capping agent. Angew. Chem. Int. Ed. Engl. 2011, 50, 10560-4.
27. Segall, M.; Lindan, P. J.; Probert, M. A.; et al. First-principles simulation: ideas, illustrations and the CASTEP code. J. Phys. Condens. Matter. 2002, 14, 2717.
28. Perdew, J. P.; Ernzerhof, M.; Burke, K. Rationale for mixing exact exchange with density functional approximations. J. Chem. Phys. 1996, 105, 9982-5.
29. Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 1996, 77, 3865.
30. Vanderbilt, D. Soft self-consistent pseudopotentials in a generalized eigenvalue formalism. Phys. Rev. B. 1990, 41, 7892.
31. Kresse, G.; Furthmüller, J. Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set. Comput. Mater. Sci. 1996, 6, 15-50.
32. Zhou, Y.; Wei, F.; Qi, H.; et al. Peripheral-nitrogen effects on the Ru1 centre for highly efficient propane dehydrogenation. Nat. Catal. 2022, 5, 1145-56.
33. Guo, C.; Zhang, T.; Deng, X.; et al. Electrochemical CO2 reduction to C1 products on single Nickel/Cobalt/Iron-doped graphitic carbon nitride: a DFT study. ChemSusChem 2019, 12, 5126-32.
34. Lancet, D.; Pecht, I. Spectroscopic and immunochemical studies with nitrobenzoxadiazolealanine, a fluorescent dinitrophenyl analogue. Biochemistry 1977, 16, 5150-7.
35. Lu, Z.; Chen, G.; Siahrostami, S.; et al. High-efficiency oxygen reduction to hydrogen peroxide catalysed by oxidized carbon materials. Nat. Catal. 2018, 1, 156-62.
36. Liu, X.; Huang, L.; Ma, Y.; et al. Enable biomass-derived alcohols mediated alkylation and transfer hydrogenation. Nat. Commun. 2024, 15, 7012.
37. Song, P.; Hu, B.; Zhao, D.; et al. Modulating the asymmetric atomic interface of copper single atoms for efficient CO2 electroreduction. ACS. Nano. 2023, 17, 4619-28.
38. Zhang, X.; Xia, M.; Liu, T.; et al. Copper hexacyanoferrate as ultra-high rate host for aqueous ammonium ion storage. Chem. Eng. J. 2021, 421, 127767.
39. Yang, F.; Ma, X.; Cai, W. B.; Song, P.; Xu, W. Nature of oxygen-containing groups on carbon for high-efficiency electrocatalytic CO2 reduction reaction. J. Am. Chem. Soc. 2019, 141, 20451-9.
40. Cheng, X. F.; He, J. H.; Ji, H. Q.; et al. Coordination symmetry breaking of single-atom catalysts for robust and efficient nitrate electroreduction to ammonia. Adv. Mater. 2022, 34, e2205767.
41. Xie, C.; Lin, L.; Huang, L.; et al. Zn-Nx sites on N-doped carbon for aerobic oxidative cleavage and esterification of C(CO)-C bonds. Nat. Commun. 2021, 12, 4823.
42. Rehr, J. J.; Albers, R. C. Theoretical approaches to x-ray absorption fine structure. Rev. Mod. Phys. 2000, 72, 621.
43. Wang, Z.; Li, Y.; Zhao, X.; et al. Localized alkaline environment via in situ electrostatic confinement for enhanced CO2-to-ethylene conversion in neutral medium. J. Am. Chem. Soc. 2023, 145, 6339-48.
44. Wen, G.; Ren, B.; Wang, X.; et al. Continuous CO2 electrolysis using a CO2 exsolution-induced flow cell. Nat. Energy. 2022, 7, 978-88.
45. Sinthika, S.; Vala, S. T.; Kawazoe, Y.; Thapa, R. CO oxidation prefers the eley-rideal or langmuir-hinshelwood pathway: monolayer vs thin film of SiC. ACS. Appl. Mater. Interfaces. 2016, 8, 5290-9.
46. Fan, Q.; Zhang, M.; Jia, M.; Liu, S.; Qiu, J.; Sun, Z. Electrochemical CO2 reduction to C2+ species: heterogeneous electrocatalysts, reaction pathways, and optimization strategies. Mater. Today. Energy. 2018, 10, 280-301.
47. Li, M.; Zhang, F.; Kuang, M.; et al. Atomic Cu sites engineering enables efficient CO2 electroreduction to methane with high CH4/C2H4 ratio. Nanomicro. Lett. 2023, 15, 238.
48. Jeon, S. S.; Kang, P. W.; Klingenhof, M.; Lee, H.; Dionigi, F.; Strasser, P. Active surface area and intrinsic catalytic oxygen evolution reactivity of NiFe LDH at reactive electrode potentials using capacitances. ACS. Catal. 2023, 13, 1186-96.
49. Mao, X.; Wijethunge, D.; Zhang, L.; et al. Metal-free graphene/boron nitride heterointerface for CO2 reduction: surface curvature controls catalytic activity and selectivity. EcoMat 2020, 2, e12013.
50. Xun, W.; Yang, X.; Jiang, Q.; Wang, M.; Wu, Y.; Li, P. Single-atom-anchored two-dimensional MoSi2N4 monolayers for efficient electroreduction of CO2 to formic acid and methane. ACS. Appl. Energy. Mater. 2023, 6, 3236-43.
51. Guan, A.; Fan, Y.; Xi, S.; et al. Nitrogen-adsorbed hydrogen species promote CO2 methanation on Cu single-atom electrocatalyst. ACS. Mater. Lett. 2023, 5, 19-26.
52. Luo, Y.; Yang, J.; Qin, J.; et al. Cobalt phthalocyanine promoted copper catalysts toward enhanced electro reduction of CO2 to C2: synergistic catalysis or tandem catalysis? J. Energy. Chem. 2024, 92, 499-507.
53. Zhou, L.; Lv, R. Rational catalyst design and interface engineering for electrochemical CO2 reduction to high-valued alcohols. J. Energy. Chem. 2022, 70, 310-31.
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Qin, J.; Hu, X.; Miao, K.; Kang, X. Oxygen coordinated Cu single atom catalysts: a superior catalyst towards electrochemical CO2 reduction for methane production. Microstructures 2025, 5, 2025022. http://dx.doi.org/10.20517/microstructures.2024.70
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