A large π-conjugated ligand in metal-organic framework as opticalswitch to regulate the electron transfer pathway for highly selective reduction of CO2 to CH4

doi:10.21203/rs.3.rs-334383/v1

Download PDF

Article

A large π-conjugated ligand in metal-organic framework as opticalswitch to regulate the electron transfer pathway for highly selective reduction of CO2 to CH4

https://doi.org/10.21203/rs.3.rs-334383/v1

This work is licensed under a CC BY 4.0 License

Version 1

posted

You are reading this latest preprint version

Here, we report a Cu-based metal-organic framework (Cu-DBC), constructed by the large π-conjugated ligand dibenzo-[g,p]chrysene-2,3,6,7,10,11,14,15-octaol and the square-pyramidal CuO5 nodes, as the photo-coupled electrocatalysts for CO2 reduction to CH4. Under visible light, it exhibits high performance for photocatalytic reduction of CO2 to CH4 with selectivity of 100% and rate of 1.04 μmol g-1 h-1, without additional photosensitizer. Importantly, at -1.4 V vs. RHE, it exhibits high performance for photo-coupled electroreduction of CO2 to CH4 with a Faradaic efficiency (CH4) of 93% and current density of 10.4 A g-1. Theoretical calculations, in-situ infrared spectroscopy investigation and Mott–Schottky measurements showed that the large conjugated ligand in Cu-DBC has the suitable lowest unoccupied molecular orbital (LUMO) to match well with the reduction potential of CO2/CH4 and serves as a photoswitch to regulate electron transfer pathway to the metal center, resulting highly selective photocatalytic reduction or photo-coupled electroreduction of CO2 to CH4.

Catalysis

Electrochemistry

Visible Light

Photocatalytic Reduction

in-situ Infrared Spectroscopy

Mott-Schottky Measurements

Lowest Unoccupied Molecular Orbital

Photoswitch

The increase of atmospheric CO₂ has a severe impact on global climate and ecological environment.^1-6 Scientists have carried out extensive researches on catalytic transformations of CO₂ molecules into high value-added chemicals, such as methane^7-8 and ethylene.⁹ However, the CO₂ reduction to hydrocarbons usually involves multi-electron transfer processes (e.g. 8 electrons for CH₄ and 12 electrons for C₂H₄), leading to slow kinetics and high overpotential.¹⁰ Compared with traditional methods, such as thermal catalysis,¹¹ photocatalysis^12-13 and electrocatalysis,^14-15 the photo-coupled electrocatalytic CO₂ reduction (PECR) is a competitive method.^16-18 It has been suggested that light can induce the band bending,¹⁹ thus reducing overpotential for CO₂ reduction and changing the catalytic pathways. In addition, the electrons and holes can be directionally separated in the external field, facilitating charge separation.²⁰ However, the studies in this field are very limited and challenging. Therefore, the development of new photo-coupled electrocatalyst system for CO₂ reduction is urgently necessary.

CO₂ reduction can generate a variety of products such as HCOOH, CO, CH₄ and C₂H₄, etc. To date, most of reported PECR catalysts were shown to convert CO₂ to CO or HCOOH, rather than high-value-added chemicals (e.g., CH₄ and C₂ products).^{17, 21-23} From the point of thermodynamics, it is possible to achieve high selectivity of CH₄ by rationally designing an electrocatalyst with the appropriate lowest unoccupied molecular orbital (LUMO) matching with the reduction potential of CO₂/CH₄ (-0.24 V) (Scheme 1). Among all the metal catalysts, Cu has been demonstrated to be capable of converting CO₂ into CH₄ and C₂ species, which is related to the appropriate interaction of *CO intermediate with Cu catalytic sites, and making it possible for further hydrogenation rather than desorption to produce CO or HCOOH.^8-9 Based on the above analysis, both photosensitive units with suitable LUMO energy levels and copper-based active sites are required for a PECR catalyst to have high activity and high selectivity in CO₂reduction into hydrocarbons. Metal-organic frameworks (MOFs) are constructed by self-assembly of metal ions or metal clusters with organic linkers.^24-26 Through altering ligands or catalytically active sites can expediently lead to various functional MOFs, making them the promising catalysts for PECR. Some organic materials bearing large π-conjugated structures usually possess narrow band gaps,^27-31 thus making the LUMO energy levels may match well with the reduction potential of CO₂/CH₄. Therefore, a MOF constructed by the copper ions and large π-conjugated ligands may be anticipated to serve as an ideal model for studying and realizing light-induced improvement of the electrocatalytic efficiency for reducing CO₂ to CH₄.

(H₂NC₂H₆)₆[Cu₂O(dbc)] (Cu-DBC, H₈dbc = dibenzo-[g,p]chrysene-2,3,6,7,10,11,14,15-octaol) possesses a 4-fold interpenetration structure,³² in which each dbc^8- linker coordinates with four copper atoms, each copper ion is coordinated by four oxygen atoms from two catecholate ligands in the same layer and a single oxygen bridge in a distorted square-pyramidal fashion to form a CuO₅ node, and a pair of copper atoms from two adjacent layers are connected by the single oxygen bridges (Figure 1a-b). Such a 3D framework structure based on large π-conjugated organic ligands and square-pyramidal CuO₅ nodes could be a potential PECR catalyst. In this work, Cu-DBC was employed to investigate the structure and performance for selective conversion of CO₂. Interestingly, with the assistance of light, the Faradaic efficiency (FE) of CH₄ and the current density were significantly enhanced over a wide potential range compared to those under the dark environment for Cu-DBC, indicating that the coupling of light energy plays an important role.

Cu-DBC was prepared by hydrothermal method according to the literature.³² The purity of the as-prepared sample was demonstrated by the scanning electron microscopy (SEM) images and powder X-ray diffraction (PXRD) measurement (Figure S2-3). The electron paramagnetic resonance (EPR) spectrum was consistent with X-ray photoelectron spectroscopy (XPS) (Figure S4), indicating the existence of Cu(II) in the synthesized samples. To study the potential semiconductive property of Cu-DBC, band gap energy (E_g) was determined to be 1.68 eV by Tauc plot (Figure S5). The Mott–Schottky measurements revealed that Cu-DBC was a typical n-type semiconductor and its LUMO position located in -0.27 V vs. RHE, which is very near to the reduction potential of CO₂/CH₄ (-0.24 V) (Figure 1c). Additionally, we conducted a photocurrent response test to investigate the light absorption capabilities of Cu-DBC, as shown in Figure 1d, revealing that the current density increases obviously under the trigger of light excitation, indicating that effective carrier generation and transfer in Cu-DBC.³³

In order to investigate the photocatalytic activity of Cu-DBC, we conducted a photocatalytic CO₂RR in a quartz cell with saturated CO₂, triethanolamine (TEOA) as sacrificial electron donor, and without photosensitizer. As shown in Figure S6, the amount of CH₄was 0.025 μmol (i.e. 1.04 μmol g^-1∙h^-1) after 24 hrs and only trace CO was detected, suggesting that Cu-DBC is capable of converting CO₂ into CH₄ with nearly 100% selectivity under visible-light irradiation. However, the reaction rate is poor, which might be ascribed to the limited kinetic process.³⁴ It is worth mentioning that the applied bias voltage can promote the separation of photogenerated electrons and holes and enhance the photocatalytic efficiency.^35-36 Therefore, we further evaluated the photoelectrochemical reduction of CO₂ for Cu-DBC.

The photoelectrochemical reduction of CO₂ was tested in 0.1 M KHCO₃ aqueous solution. All the potentials mentioned in this work are based on the reversible hydrogen electrode (RHE). The linear sweep voltammetry (LSV) (Figure 2a) revealed that compared with dark condition, the current density of Cu-DBC increases evidently under visible light irradiation (λ > 400 nm). ¹H nuclear magnetic resonance (NMR) spectrum (Figure S7) and gas chromatography results (Figures 2b-c) revealed that no liquid-phase products were generated during CO₂ reduction over Cu-DBC. The FEs of different reduced products were tested (Figure 2b), showing the total FEs of gaseous products at all potentials are ~100%. In particular, the FE of CH₄ can reach up to 93.2% with the current density of 10.4 A g^-1 at -1.4 V, which is the best one among all known MOFs for CH₄ production in CO₂RR (Table S1). Actually, to our best knowledge, only a FN-CTF-400 compound exhibits a higher FE (FE_CH4 = 99.3%) than Cu-DBC, but with a current density of only 0.2 A g^-1.³⁷ In order to explore the effect of light irradiation, the electrocatalytic CO₂RR was tested in the same potential range without light irradiation (Figure 2c). By comparison, the maximal FE and current density of CH₄ significantly decrease from ~93% to ~54%, and from 10.4 to 3.9 A g^-1, respectively, at -1.4 V. This phenomenon indicates that the large π-conjugated ligand could serve as a photoswitch to regulate electron transfer pathway to the metal center, and coupling light with electric field can indeed improve the catalytic performance of Cu-DBC for CO₂RR.

In addition to high activity and selectivity, long-term stability is an important factor for PECR catalysts. The i-t test was conducted at -1.4 V for 4 hours (Figure 2d), and it showed the current density was changed into 97% of the previous level. Meanwhile, the PXRD patterns, transmission electron microscopy (TEM) images and XPS analysis of Cu-DBC showed negligible change and no generation of Cu₂O or Cu cluster after the CO₂RR test for 4 hours (Figure S8-S9), suggesting that Cu-DBC is stable and the catalytical performance can be ascribed to the MOF rather than Cu₂O or Cu clusters. In the literature,¹⁴ the square-planar CuO₄ nodes of MOF was unstable during the electrocatalytic process, highlighting the high stability of the square-pyramidal CuO₅ nodes in Cu-DBC.

A variety of products can be produced in CO₂ reduction reaction due to the different reaction intermediates formed over the catalysts. In order to investigate the reaction paths occurred on the Cu-DBC, in-situ attenuated total reflection infrared (ATR-FTIR) spectral measurements were performed with a home-made cell. Three bands located at 1288, 1366~1383, and 1616 cm^-1 are associated with the OH-deformation, C−O stretching vibration and O−C=O asymmetric stretching vibration of *COOH intermediate, respectively, while a weaker band at 1020 cm^-1 belongs to *CHO intermediate (Figures 3a,b).^38-40 Especially, both the *COOH and *CHO groups are crucial intermediates for the reduction of CO₂ to CH₄. Based on the ATR-FTIR spectral analysis, a possible reaction mechanism of the reduction of CO₂ is proposed in Figure 3c. In words, a CO₂molecule can be physically adsorbed on the square-pyramidal CuO₅ node of Cu-DBC and undergoes a proton-coupled electron transfer process to generate a *COOH intermediate, and then a *CO intermediate, which is successively hydrogenated into *CHO, *OCH₂ and *OCH₃intermediates, and ultimately achieve the 8-electron transfer process to generate CH₄.

In order to confirm the reaction mechanism, we used periodic density functional theory (PDFT) to simulate the reaction path and evaluate the corresponding energy barriers. As shown in the Figure 3d, the hydrogenation of *CO to *CHO involves a minimum barrier of -0.39 eV, while the production of CO involves a higher barrier of 0.18 eV. The low energy barrier allows the hydrogenation of *CO to be the main reaction. In fact, the energy barriers of hydrogenations of other intermediates are all lower than that of desorption (Figure 3d), which finally results in CH₄ as the main product rather than formic acid, formaldehyde or methanol. The structures of all intermediates obtained by PDFT calculations are illustrated in Figure S10. Comparing with the high energy barrier of hydrogen evolution reaction (Figure S11), the catalytic reduction of CO₂ to CH₄ involves lower energy, which is consistent with the experimental results. These facts suggest that the square-pyramidal CuO₅ nodes of Cu-DBC indeed can serve as the active sites for catalytic reduction of CO₂ to CH₄.

Finally, the significant increase of the FE for CH₄ when coupling light with electrocatalytic CO₂RR can be rationalized to that the formation of methane is thermodynamically feasible, but it must undergo a slow 8-electron transfer process. Through analyzing the frontier orbitals of Cu-DBC, it can be seen that the highest occupied molecular orbital (HOMO) is mainly located on the large π-conjugated ligand, and the lowest unoccupied molecular orbital (LUMO) is mainly located on the metal center. Under dark condition, electrons can enter the LUMO orbital but need a high overpotential to cross the HOMO-LUMO energy gap, resulting in a poor methane yield under dark condition. When Cu-DBC is light irradiated, the electrons in HOMO orbital can harvest photons and jump into the LUMO orbitals that match with the reduction potential of CH₄, then can activate and reduce CO₂ molecule into CH₄ with a high selectivity.

To clarify the mechanism of photo-electrocatalysis and the effect of visible light, the electronic properties of S1 and T1 excited states of Cu-BDC were further calculated with PDFT. Both S1 and T1 exhibit clearly the ligand-to-metal charge-transfer (LMCT) excitation characteristic, which obviously facilitates the electron-flow and CO₂ activation occurring on the square-pyramidal CuO₅ node. When Cu-DBC is light irradiated, the large π-conjugated ligand is first excited from the S₀ ground state to the S₁ state, and then spontaneously transformed to T₁ triplet state through the process of intersystem crossing. The energy gap between S₀ and S₁ is 1.71 eV, which is consistent with the band gap (1.68 eV) calculated from the UV-vis absorption spectrum, confirming the accuracy of the calculations. Since all the photophysical processes occur much faster than the electrocatalysis process, it can be proposed that the photo-coupled electrocatalysis of CO₂ proceeds mainly from the T₁ state rather than the S₀ state. The energy of T₁ is 1.13 eV higher than the S₀ state, suggesting that under light conditions, Cu-DBC will be excited to a higher energy state. Such high energy can enhance the electron transfer from the ligand to the active center, resulting in the improvement of current density (Figure 2a). These explain the inherent reason why Cu-DBC exhibits high performance for electrocatalytic reduction of CO₂ to CH₄.

In summary, a Cu-catecholate based MOF with active CuO₅ sites exhibits excellent activity and selectivity for CH₄ in PECR measurements. Compared with the condition of dark, the FE(CH₄) and current density increase very significantly upon light irradiation. Experimental and theoretical studies reveal that the high performance for PECR is ascribed to the highly catalytical activity of the CuO₅ node, the suitable conduction band edge position and the external light-field can enhance the electron transfer to the adsorbed CO₂. The results provide a new strategy to design and utilize photo-electrocatalysts with light harvesting and catalytic active sites for converting CO₂ into high-valued chemicals.

Materials and general methods. The ligand dibenzo-[g,p]chrysene-2,3,6,7,10,11,14,15-octaol was synthesized according to the literature^.41 Other reagents were commercially available and without further purification. Power X-ray diffraction (PXRD) patterns were collected on a Bruker D8 Advance diffractometer (Cu Kα). X-ray photoelectron spectroscopy (XPS) measurements were performed on an ESCALAB 250 spectrometer. A SU8010 scanning electron microscope was utilized to investigate the morphology of Cu-DBC. High resolution images of microcrystalline powder of Cu-DBC before and after CO₂ reduction reaction were obtained by a transmission electron microscope (TEM). ¹H Nuclear magnetic resonance (¹H NMR) measurements were performed on a Bruker advance III. Attenuated total reflection infrared (ATR-FTIR) spectra were recorded on a Nicolet 6700 (Thermo Fisher) to study the reaction intimidates formed over Cu-DBC in the electrochemical measurements.

Synthesis of Cu-DBC. dibenzo-[g,p]chrysene-2,3,6,7,10,11,14,15-octaol (8.6 mg) and Cu(OAc)₂ (6 mg) were dissolved in 500 μL DMF and 2 mL deionized water. After ultrasonic treatment for 30 minutes, the vessel was placed in an oven with the temperature of 85 °C for 72 hours. Then the MOF was separated from the reaction mixtures by washing with water and dried overnight in 60 °C to obtain the black product.

1 Asadi, M. et al. Nanostructured transition metal dichalcogenide electrocatalysts for CO₂ reduction in ionic liquid. Science 353, 467. (2016)

2 Mikkelsen, M.; Jørgensen, M.; Krebs, F. C. The teraton challenge. A review of fixation and transformation of carbon dioxide. Energy Environ. Sci. 3, 43-81. (2010)

3 Leung, D. Y. C.; Caramanna, G.; Maroto-Valer, M. M. An overview of current status of carbon dioxide capture and storage technologies. Renew. Sust. Energ. Rev. 39, 426-443. (2014)

4 Kainiemi, L.; Eloneva, S.; Toikka, A.; Levänen, J.; Järvinen, M. Opportunities and obstacles for CO₂ mineralization: CO₂ mineralization specific frames in the interviews of Finnish carbon capture and storage (CCS) experts. J. Clean. Prod. 94, 352-358. (2015)

5 Li, C. W.; Ciston, J.; Kanan, M. W. Electroreduction of carbon monoxide to liquid fuel on oxide-derived nanocrystalline copper. Nature 508, 504-507. (2014)

6 Lin, S. et al. Covalent organic frameworks comprising cobalt porphyrins for catalytic CO₂ reduction in water. Science 349, 1208. (2015)

7 Jiang, K. et al. Metal ion cycling of Cu foil for selective C–C coupling in electrochemical CO₂ reduction. Nat. Catal. 1, 111-119. (2018)

8 Nie, X.; Esopi, M. R.; Janik, M. J.; Asthagiri, A. Selectivity of CO₂ reduction on copper electrodes: the role of the kinetics of elementary steps. Angew. Chem. Int. Ed. 52, 2459-62. (2013)

9 Calle-Vallejo, F.; Koper, M. T. Theoretical considerations on the electroreduction of CO to C₂ species on Cu(100) electrodes. Angew. Chem. Int. Ed. 52, 7282-5. (2013)

10 Kim, C. et al. Alloy Nanocatalysts for the Electrochemical Oxygen Reduction (ORR) and the Direct Electrochemical Carbon Dioxide Reduction Reaction (CO₂RR). Adv. Mater. 31, e1805617. (2019)

11 Wesselbaum, S.; vom Stein, T.; Klankermayer, J.; Leitner, W. Hydrogenation of Carbon Dioxide to Methanol by Using a Homogeneous Ruthenium–Phosphine Catalyst. Angew. Chem. Int. Ed. 51, 7499-7502. (2012)

12 Wang, Y. et al. Hydroxide Ligands Cooperate with Catalytic Centers in Metal–Organic Frameworks for Efficient Photocatalytic CO₂ Reduction. J. Am. Chem. Soc. 140, 38-41. (2017)

13 Zhong, H. et al. Covalent Organic Framework Hosting Metalloporphyrin‐Based Carbon Dots for Visible‐Light‐Driven Selective CO₂ Reduction. Adv. Funct. Mater. 30, e2002654. (2020)

14 Nam, D. H. et al. Metal-Organic Frameworks Mediate Cu Coordination for Selective CO₂ Electroreduction. J. Am. Chem. Soc. 140, 11378-11386. (2018)

15 Zhong, H. et al. Synergistic electroreduction of carbon dioxide to carbon monoxide on bimetallic layered conjugated metal-organic frameworks. Nat. Commun. 11, 1409. (2020)

16 Schreier, M. et al. Covalent Immobilization of a Molecular Catalyst on Cu₂O Photocathodes for CO₂ Reduction. J. Am. Chem. Soc. 138, 1938-46. (2016)

17 Lan, Y. Q. et al. Ultrastable Dioxin-Linked Metallophthalocyanine Covalent Organic Frameworks as Photo-Coupled Electrocatalysts for CO₂ Reduction. Angew. Chem. Int. Ed. (2020)

18 Chu, S. et al. Photoelectrochemical CO₂ Reduction into Syngas with the Metal/Oxide Interface. J. Am. Chem. Soc. 140, 7869-7877. (2018)

19 Huang, X.; Shen, Q.; Liu, J.; Yang, N.; Zhao, G. A CO₂ adsorption-enhanced semiconductor/metal-complex hybrid photoelectrocatalytic interface for efficient formate production. Energy Environ. Sci. 9, 3161-3171. (2016)

20 Jang, J.-W. et al. Aqueous-Solution Route to Zinc Telluride Films for Application to CO₂ Reduction. Angew. Chem. Int. Ed. 53, 5852-5857. (2014)

21 Chang, X. et al. Stable Aqueous Photoelectrochemical CO₂ Reduction by a Cu₂O Dark Cathode with Improved Selectivity for Carbonaceous Products. Angew. Chem. Int. Ed. 55, 8840-5. (2016)

22 Yang, D. et al. Visible-light-switched electron transfer over single porphyrin-metal atom center for highly selective electroreduction of carbon dioxide. Nat. Commun. 10, 3844. (2019)

23 Zhou, B. et al. A GaN:Sn nanoarchitecture integrated on a silicon platform for converting CO₂ to HCOOH by photoelectrocatalysis. Energy Environ. Sci. 12, 2842-2848. (2019)

24 Furukawa, H.; Cordova, K. E.; O'Keeffe, M.; Yaghi, O. M. The chemistry and applications of metal-organic frameworks. Science 341, 1230444. (2013)

25 Yang, D.-A.; Cho, H.-Y.; Kim, J.; Yang, S.-T.; Ahn, W.-S. CO₂ capture and conversion using Mg-MOF-74 prepared by a sonochemical method. Energy Environ. Sci. 5, 6465-6473. (2012)

26 Zhang, J.-P.; Zhang, Y.-B.; Lin, J.-B.; Chen, X.-M. Metal Azolate Frameworks: From Crystal Engineering to Functional Materials. Chem. Rev. 112, 1001-1033. (2012)

27 Li, Y. et al. Integrating bimetallic AuPd nanocatalysts with a 2D aza-fused π-conjugated microporous polymer for light-driven benzyl alcohol oxidation. Chinese Chem Lett 31, 231-234. (2020)

28 Mikie, T.; Osaka, I. Small-bandgap quinoid-based π-conjugated polymers. J. Mater. Chem. C 8, 14262-14288. (2020)

29 Giri, D.; Raut, S. K.; Patra, S. K. Diketopyrrolopyrrole/perylene-diimide and thiophene based D-π-A low bandgap polymer sensitizers for application in dye sensitized solar cells. Dyes Pigments 174, 108032. (2020)

30 Zheng, L. et al. Solution-processed broadband polymer photodetectors with a spectral response of up to 2.5 μm by a low bandgap donor–acceptor conjugated copolymer. J. Mater. Chem. C 6, 3634-3641. (2018)

31 Weldeab, A. O. et al. Pyridine-terminated low gap π-conjugated oligomers: design, synthesis, and photophysical response to protonation and metalation. Org. Chem. Front. 5, 3170-3177. (2018)

32 Liu, J. et al. Conjugated Copper-Catecholate Framework Electrodes for Efficient Energy Storage. Angew. Chem. Int. Ed. 59, 1081-1086. (2020)

33 Pan, A. et al. CsPbBr₃ Perovskite Nanocrystal Grown on MXene Nanosheets for Enhanced Photoelectric Detection and Photocatalytic CO₂ Reduction. J. Phys. Chem. Lett. 10, 6590-6597. (2019)

34 Chang, K.; Zhang, H.; Chen, J. G.; Lu, Q.; Cheng, M.-J. Constant Electrode Potential Quantum Mechanical Study of CO₂ Electrochemical Reduction Catalyzed by N-Doped Graphene. ACS Catal. 9, 8197-8207. (2019)

35 Cortes, M. A. L. R. M. et al. Photoelectrochemical reduction of CO₂ with TiNT. Mat Sci in Semicon Proc 108, (2020)

36 Xie, S.; Zhang, Q.; Liu, G.; Wang, Y. Photocatalytic and photoelectrocatalytic reduction of CO₂ using heterogeneous catalysts with controlled nanostructures. Chem. Commun. 52, 35-59. (2016)

37 Wang, Y.; Chen, J.; Wang, G.; Li, Y.; Wen, Z. Perfluorinated Covalent Triazine Framework Derived Hybrids for the Highly Selective Electroconversion of Carbon Dioxide into Methane. Angew. Chem. Int. Ed. 57, 13120-13124. (2018)

38 Yi, J. D. et al. Highly Selective CO₂ Electroreduction to CH₄ by In Situ Generated Cu₂O Single-Type Sites on a Conductive MOF: Stabilizing Key Intermediates with Hydrogen Bonding. Angew. Chem. Int. Ed. 59, 23641-23648. (2020)

39 Li, X. et al. Selective visible-light-driven photocatalytic CO₂ reduction to CH₄ mediated by atomically thin CuIn₅S₈ layers. Nat. Energy 4, 690-699. (2019)

40 Wang, T. et al. Photoreduction of CO₂ over the well-crystallized ordered mesoporous TiO₂ with the confined space effect. Nano Energy 9, 50-60. (2014)

41 Varshney, S. K.; Nagayama, H.; Takezoe, H.; Prasad, V. Octasubstituted dibenzochrysenes: discotic liquid crystals with a twisted core. Liq. Cryst. 36, 1409-1415. (2009)

Acknowledgements

This work was supported by the NSFC (21890380, 21821003), Local Innovative and Research Teams Project of Guangdong Pearl River Talents Program (2017BT01C161), and Guangdong Natural Science Funds for Distinguished Young Scholar (2018B030306009).

Author contributions

P.Q.L. designed the research. Y.Y.L., H.L.Z. and N.Y.H. performed syntheses and measurements. Y.Y.L., P.Q.L. and X.M.C. wrote the manuscript.

Competing financial interests

The authors declare no competing financial interests.

Scheme 1 is available in the Supplementary Files.

There is NO Competing Interest.

Scheme1.png
Scheme 1│ Schematic energy-level diagram showing HER and CO2RR reaction pathways for different products.
SI.pdf
Supporting Information

Download PDF

Version 1

posted

You are reading this latest preprint version

A large π-conjugated ligand in metal-organic framework as opticalswitch to regulate the electron transfer pathway for highly selective reduction of CO2 to CH4

Status:

Version 1

Abstract

Figures

Introduction

Results

Discussion

Methods

References

Declarations

Scheme

Additional Declarations

Supplementary Files

Status:

Version 1