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Metal ion cycling of Cu foil for selective C–C coupling in electrochemical CO2 reduction

Nature Catalysis volume 1, pages 111–119 (2018)Cite this article

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Abstract

Electrocatalytic CO2 reduction to higher-value hydrocarbons beyond C1 products is desirable for applications in energy storage, transportation and the chemical industry. Cu catalysts have shown the potential to catalyse C–C coupling for C2+ products, but still suffer from low selectivity in water. Here, we use density functional theory to determine the energetics of the initial C–C coupling steps on different Cu facets in CO2 reduction, and suggest that the Cu(100) and stepped (211) facets favour C2+ product formation over Cu(111). To demonstrate this, we report the tuning of facet exposure on Cu foil through the metal ion battery cycling method. Compared with the polished Cu foil, our 100-cycled Cu nanocube catalyst with exposed (100) facets presents a sixfold improvement in C2+ to C1 product ratio, with a highest C2+ Faradaic efficiency of over 60% and H2 below 20%, and a corresponding C2+ current of more than 40 mA cm–2.

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Fig. 1: DFT simulations of C–C coupling on Cu facets.
Fig. 2: Cu2+ ion battery cycling of Cu2O and Cu nanocubes.
Fig. 3: Cross-section FIB and TEM characterizations of Cu2O and Cu nanocubes.
Fig. 4: Electrocatalytic CO2RR on polished Cu foil, 10-cycle Cu and 100-cycle Cu.

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References

  1. Obama, B. The irreversible momentum of clean energy. Science 355, 126–129 (2017).

    Article  CAS  Google Scholar 

  2. Chu, S., Cui, Y. & Liu, N. The path towards sustainable energy. Nat. Mater. 16, 16–22 (2017).

    Article  Google Scholar 

  3. Lewis, N. S. Research opportunities to advance solar energy utilization. Science 351, aad1920 (2016).

    Article  Google Scholar 

  4. Liu, C., Colón, B. C., Ziesack, M., Silver, P. A. & Nocera, D. G. Water splitting–biosynthetic system with CO2 reduction efficiencies exceeding photosynthesis. Science 352, 1210–1213 (2016).

    Article  CAS  Google Scholar 

  5. Cook, T. R. et al. Solar energy supply and storage for the legacy and nonlegacy worlds. Chem. Rev. 110, 6474–6502 (2010).

    Article  CAS  Google Scholar 

  6. Concepcion, J. J., House, R. L., Papanikolas, J. M. & Meyer, T. J. Chemical approaches to artificial photosynthesis. Proc. Natl Acad. Sci. USA 109, 15560–15564 (2012).

    Article  CAS  Google Scholar 

  7. Lewis, N. S. & Nocera, D. G. Powering the planet: chemical challenges in solar energy utilization. Proc. Natl Acad. Sci. USA 103, 15729–15735 (2006).

    Article  CAS  Google Scholar 

  8. Sakimoto, K. K., Wong, A. B. & Yang, P. Self-photosensitization of nonphotosynthetic bacteria for solar-to-chemical production. Science 351, 74–77 (2016).

    Article  CAS  Google Scholar 

  9. Rosen, B. A. et al. Ionic liquid-mediated selective conversion of CO2 to CO at low overpotentials. Science 334, 643–644 (2011).

    Article  CAS  Google Scholar 

  10. Hori, Y. in Modern Aspects of Electrochemistry Modern Aspects of Electrochemistry (eds Vayenas, C. G., White, R. E. & Gamboa-Aldeco, M. E.) 89–189 (Springer, New York, 2008).

  11. Zhu, D. D., Liu, J. L. & Qiao, S. Z. Recent advances in inorganic heterogeneous electrocatalysts for reduction of carbon dioxide. Adv. Mater. 28, 3423–3452 (2016).

    Article  CAS  Google Scholar 

  12. Hori, Y., Takahashi, I., Koga, O. & Hoshi, N. Selective formation of C2 compounds from electrochemical reduction of CO2 at a series of copper single crystal electrodes. J. Phys. Chem. B 106, 15–17 (2002).

    Article  CAS  Google Scholar 

  13. Jiang, K. et al. Transition-metal single atoms in a graphene shell as active centers for highly efficient artificial photosynthesis. Chem https://doi.org/10.1016/j.chempr.2017.09.014 (2017).

  14. Liu, M. et al. Enhanced electrocatalytic CO2 reduction via field-induced reagent concentration. Nature 537, 382–386 (2016).

    Article  CAS  Google Scholar 

  15. Saberi Safaei, T. et al. High-density nanosharp microstructures enable efficient CO2 electroreduction. Nano Lett. 16, 7224–7228 (2016).

    Article  CAS  Google Scholar 

  16. Gao, S. et al. Partially oxidized atomic cobalt layers for carbon dioxide electroreduction to liquid fuel. Nature 529, 68–71 (2016).

    Article  CAS  Google Scholar 

  17. Chen, Y., Li, C. W. & Kanan, M. W. Aqueous CO2 reduction at very low overpotential on oxide-derived Au nanoparticles. J. Am. Chem. Soc. 134, 19969–19972 (2012).

    Article  CAS  Google Scholar 

  18. Lin, S. et al. Covalent organic frameworks comprising cobalt porphyrins for catalytic CO2 reduction in water. Science 349, 1208–1213 (2015).

    Article  CAS  Google Scholar 

  19. Kornienko, N. et al. Metal–organic frameworks for electrocatalytic reduction of carbon dioxide. J. Am. Chem. Soc. 137, 14129–14135 (2015).

    Article  CAS  Google Scholar 

  20. Zhang, S. et al. Polyethylenimine-enhanced electrocatalytic reduction of CO2 to formate at nitrogen-doped carbon nanomaterials. J. Am. Chem. Soc. 136, 7845–7848 (2014).

    Article  CAS  Google Scholar 

  21. Zhang, S., Kang, P. & Meyer, T. J. Nanostructured tin catalysts for selective electrochemical reduction of carbon dioxide to formate. J. Am. Chem. Soc. 136, 1734–1737 (2014).

    Article  CAS  Google Scholar 

  22. Lei, F. et al. Metallic tin quantum sheets confined in graphene toward high-efficiency carbon dioxide electroreduction. Nat. Commun. 7, 12697 (2016).

    Article  CAS  Google Scholar 

  23. Sharma, P. P. et al. Nitrogen-doped carbon nanotube arrays for high-efficiency electrochemical reduction of CO2: on the understanding of defects, defect density, and selectivity. Angew. Chem. Int. Ed. 127, 13905–13909 (2015).

    Article  Google Scholar 

  24. Zhang, X. et al. Highly selective and active CO2 reduction electrocatalysts based on cobalt phthalocyanine/carbon nanotube hybrid structures. Nat. Commun. 8, 14675 (2017).

    Article  Google Scholar 

  25. Verma, S., Kim, B., Jhong, H.-R. M., Ma, S. & Kenis, P. J. A. A gross-margin model for defining technoeconomic benchmarks in the electroreduction of CO2. ChemSusChem 9, 1972–1979 (2016).

    Article  CAS  Google Scholar 

  26. Liu, X. et al. Understanding trends in CO2 reduction on transition metals. Nat. Commun. 8, 15438 (2017).

    Article  CAS  Google Scholar 

  27. Kuhl, K. P., Cave, E. R., Abram, D. N. & Jaramillo, T. F. New insights into the electrochemical reduction of carbon dioxide on metallic copper surfaces. Energy Environ. Sci. 5, 7050–7059 (2012).

    Article  CAS  Google Scholar 

  28. Hori, Y., Takahashi, I., Koga, O. & Hoshi, N. Electrochemical reduction of carbon dioxide at various series of copper single crystal electrodes. J. Mol. Catal. A Chem. 199, 39–47 (2003).

    Article  CAS  Google Scholar 

  29. Schouten, K. J. P., Qin, Z., Gallent, E. P. & Koper, M. T. M. Two pathways for the formation of ethylene in CO reduction on single-crystal copper electrodes. J. Am. Chem. Soc. 134, 9864–9867 (2012).

    Article  CAS  Google Scholar 

  30. Calle-Vallejo, F. & Koper, M. T. M. Theoretical considerations on the electroreduction of CO to C2 species on Cu(100) electrodes. Angew. Chem. Int. Ed. 52, 7282–7285 (2013).

    Article  CAS  Google Scholar 

  31. Xie, M. S. et al. Amino acid modified copper electrodes for the enhanced selective electroreduction of carbon dioxide towards hydrocarbons. Energy Environ. Sci. 9, 1687–1695 (2016).

    Article  CAS  Google Scholar 

  32. Li, C. W. & Kanan, M. W. CO2 reduction at low overpotential on cu electrodes resulting from the reduction of thick Cu2O films. J. Am. Chem. Soc. 134, 7231–7234 (2012).

    Article  CAS  Google Scholar 

  33. 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).

    Article  CAS  Google Scholar 

  34. Ma, M., Djanashvili, K. & Smith, W. A. Controllable hydrocarbon formation from the electrochemical reduction of CO2 over Cu nanowire arrays. Angew. Chem. Int. Ed. 128, 6792–6796 (2016).

    Article  Google Scholar 

  35. Mistry, H. et al. Highly selective plasma-activated copper catalysts for carbon dioxide reduction to ethylene. Nat. Commun. 7, 12123 (2016).

    Article  Google Scholar 

  36. Huang, Y., Handoko, A. D., Hirunsit, P. & Yeo, B. S. Electrochemical reduction of CO2 using copper single-crystal surfaces: effects of CO* coverage on the selective formation of ethylene. ACS Catal. 7, 1749–1756 (2017).

    Article  CAS  Google Scholar 

  37. Roberts, F. S., Kuhl, K. P. & Nilsson, A. High selectivity for ethylene from carbon dioxide reduction over copper nanocube electrocatalysts. Angew. Chem. Int. Ed. 54, 5179–5182 (2015).

    Article  CAS  Google Scholar 

  38. Roberts, F. S., Kuhl, K. P. & Nilsson, A. Electroreduction of carbon monoxide over a copper nanocube catalyst: surface structure and pH dependence on selectivity. ChemCatChem 8, 1119–1124 (2016).

    Article  CAS  Google Scholar 

  39. Loiudice, A. et al. Tailoring copper nanocrystals towards C2 products in electrochemical CO2 reduction. Angew. Chem. Int. Ed. 55, 5789–5792 (2016).

    Article  CAS  Google Scholar 

  40. Goodpaster, J. D., Bell, A. T. & Head-Gordon, M. Identification of possible pathways for C–C bond formation during electrochemical reduction of CO2: new theoretical insights from an improved electrochemical model. J. Phys. Chem. Lett. 7, 1471–1477 (2016).

    Article  CAS  Google Scholar 

  41. Xiao, H., Cheng, T., Goddard, W. A. & Sundararaman, R. Mechanistic explanation of the pH dependence and onset potentials for hydrocarbon products from electrochemical reduction of CO on Cu (111). J. Am. Chem. Soc. 138, 483–486 (2016).

    Article  CAS  Google Scholar 

  42. Xiao, H., Cheng, T. & Goddard, W. A. Atomistic mechanisms underlying selectivities in C1 and C2 products from electrochemical reduction of CO on Cu(111). J. Am. Chem. Soc. 139, 130–136 (2017).

    Article  CAS  Google Scholar 

  43. Kortlever, R., Shen, J., Schouten, K. J. P., Calle-Vallejo, F. & Koper, M. T. M. Catalysts and reaction pathways for the electrochemical reduction of carbon dioxide. J. Phys. Chem. Lett. 6, 4073–4082 (2015).

    Article  CAS  Google Scholar 

  44. Chen, L. D., Urushihara, M., Chan, K. & Nørskov, J. Electric field effects in electrochemical CO2 reduction. ACS Catal. 6, 7133–7139 (2016).

    Article  CAS  Google Scholar 

  45. Montoya, J. H., Shi, C., Chan, K. & Norskov, J. K. Theoretical insights into a CO dimerization mechanism in CO2 electroreduction. J. Phys. Chem. Lett. 6, 2032–2037 (2015).

    Article  CAS  Google Scholar 

  46. Hinnemann, B. et al. Biomimetic hydrogen evolution:  MoS2 nanoparticles as catalyst for hydrogen evolution. J. Am. Chem. Soc. 127, 5308–5309 (2005).

    Article  CAS  Google Scholar 

  47. Kibsgaard, J. et al. Designing an improved transition metal phosphide catalyst for hydrogen evolution using experimental and theoretical trends. Energy Environ. Sci. 8, 3022–3029 (2015).

    Article  CAS  Google Scholar 

  48. Zheng, Y., Jiao, Y., Jaroniec, M. & Qiao, S. Z. Advancing the electrochemistry of the hydrogen-evolution reaction through combining experiment and theory. Angew. Chem. Int. Ed. 54, 52–65 (2015).

    Article  CAS  Google Scholar 

  49. Greeley, J., Jaramillo, T. F., Bonde, J., Chorkendorff, I. & Norskov, J. K. Computational high-throughput screening of electrocatalytic materials for hydrogen evolution. Nat. Mater. 5, 909–913 (2006).

    Article  CAS  Google Scholar 

  50. Zhang, J., Zhao, Z., Xia, Z. & Dai, L. A metal-free bifunctional electrocatalyst for oxygen reduction and oxygen evolution reactions. Nat. Nanotech. 10, 444–452 (2015).

    Article  CAS  Google Scholar 

  51. Seitz, L. C. et al. A highly active and stable IrO x /SrIrO3 catalyst for the oxygen evolution reaction. Science 353, 1011–1014 (2016).

    Article  CAS  Google Scholar 

  52. Wang, H. et al. Direct and continuous strain control of catalysts with tunable battery electrode materials. Science 354, 1031–1036 (2016).

    Article  CAS  Google Scholar 

  53. Chan, K. & Nørskov, J. K. Electrochemical barriers made simple. J. Phys. Chem. Lett. 6, 2663–2668 (2015).

    Article  CAS  Google Scholar 

  54. Schnur, S. & Groß, A. Challenges in the first-principles description of reactions in electrocatalysis. Catal. Today 165, 129–137 (2011).

    Article  CAS  Google Scholar 

  55. Hormann, N. G. et al. Some challenges in the first-principles modeling of structures and processes in electrochemical energy storage and transfer. J. Power Sources 275, 531–538 (2015).

    Article  Google Scholar 

  56. Calle-Vallejo, F. & Koper, M. T. M. First-principles computational electrochemistry: achievements and challenges. Electrochim. Acta 84, 3–11 (2012).

    Article  CAS  Google Scholar 

  57. Sandberg, R., Montoya, J. H., Chan, K. & Norskov, J. CO–CO coupling on Cu facets: strain and coverage effects. Surf. Sci. 654, 56–62 (2016).

    Article  CAS  Google Scholar 

  58. Bertheussen, E. et al. Acetaldehyde as an intermediate in the electroreduction of carbon monoxide to ethanol on oxide-derived copper. Angew. Chem. Int. Ed. 55, 1450–1454 (2016).

    Article  CAS  Google Scholar 

  59. Schouten, K. J. P., Kwon, Y., Ham, C. J. Mvd, Qin, Z. & Koper, M. T. M. A new mechanism for the selectivity to C1 and C2 species in the electrochemical reduction of carbon dioxide on copper electrodes. Chem. Sci. 2, 1902–1909 (2011).

    Article  CAS  Google Scholar 

  60. Resasco, J. et al. Promoter effects of alkali metal cations on the electrochemical reduction of carbon dioxide. J. Am. Chem. Soc. 139, 11277–11287 (2017).

    Article  CAS  Google Scholar 

  61. Norskov, J. K., Studt, F., Abild-Pedersen, F. & Bligaard, T. Fundamental Concepts in Heterogeneous Catalysis (Wiley, Hoboken, NJ, 2014).

  62. Ikemiya, N., Kubo, T. & Hara, S. In situ AFM observations of oxide film formation o n Cu(111) and Cu (100) surfaces under aqueous alkaline solutions. Surf. Sci. 323, 81–90 (1995).

    Article  CAS  Google Scholar 

  63. Zhou, G. & Yang, J. C. Formation of quasi-one-dimensional Cu2O structures by in situ oxidation of Cu(100). Phys. Rev. Lett. 89, 106101 (2002).

    Article  Google Scholar 

  64. Shang, Y. & Guo, L. Facet-controlled synthetic strategy of Cu2O-based crystals for catalysis and sensing. Adv. Sci. 2, 1500140 (2015).

    Article  Google Scholar 

  65. Huang, W.-C., Lyu, L.-M., Yang, Y.-C. & Huang, M. H. Synthesis of Cu2O nanocrystals from cubic to rhombic dodecahedral structures and their comparative photocatalytic activity. J. Am. Chem. Soc. 134, 1261–1267 (2012).

    Article  CAS  Google Scholar 

  66. Oba, F. et al. Epitaxial growth of cuprous oxide electrodeposited onto semiconductor and metal substrates. J. Am. Chem. Soc. 88, 253–270 (2005).

    CAS  Google Scholar 

  67. Manthiram, K., Beberwyck, B. J. & Alivisatos, A. P. Enhanced electrochemical methanation of carbon dioxide with a dispersible nanoscale copper catalyst. J. Am. Chem. Soc. 136, 13319–13325 (2014).

    Article  CAS  Google Scholar 

  68. Hori, Y., Takahashi, R., Yoshinami, Y. & Murata, A. Electrochemical reduction of CO at a copper electrode. J. Phys. Chem. B 101, 7075–7081 (1997).

    Article  CAS  Google Scholar 

  69. Kas, R., Kortlever, R., Yılmaz, H., Koper, M. T. M. & Mul, G. Manipulating the hydrocarbon selectivity of copper nanoparticles in CO2 electroreduction by process conditions. ChemElectroChem 2, 354–358 (2015).

    Article  CAS  Google Scholar 

  70. Henkelman, G., Uberuaga, B. P. & Jonsson, H. A climbing image nudged elastic band method for finding saddle points and minimum energy paths. J. Chem. Phys. 113, 9901–9904 (2000).

    Article  CAS  Google Scholar 

  71. Wellendorff, J. et al. Density functionals for surface science: exchange-correlation model development with Bayesian error estimation. Phys. Rev. B 85, 235149 (2012).

    Article  Google Scholar 

  72. Giannozzi, P. et al. QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials. J. Phys. Condens. Matter 21, 395502 (2009).

    Article  Google Scholar 

  73. Bahn, S. R. & Jacobsen, K. W. An object-oriented scripting interface to a legacy electronic structure code. Comput. Sci. Eng. 4, 56–66 (2002).

    Article  CAS  Google Scholar 

  74. Cramer, C. J. Essentials of Computational Chemistry (Wiley, Chichester, 2004).

  75. Ogasawara, H. et al. Structure and bonding of water on Pt(111). Phys. Rev. Lett. 89, 276102 (2002).

    Article  CAS  Google Scholar 

  76. Goedecker, S. Minima hopping: an efficient search method for the global minimum of the potential energy surface of complex molecular systems. J. Chem. Phys. 120, 9911–9917 (2004).

    Article  CAS  Google Scholar 

  77. Rossmeisl, J., Skulason, E., Bjorketun, M. E., Tripkovic, V. & Norskov, J. K. Modeling the electrified solid–liquid interface. Chem. Phys. Lett. 466, 68–71 (2008).

    Article  CAS  Google Scholar 

  78. Bengtsson, L. Dipole correction for surface supercell calculations. Phys. Rev. B 59, 12301–12304 (1999).

    Article  CAS  Google Scholar 

  79. Norskov, J. K. et al. Origin of the overpotential for oxygen reduction at a fuel-cell cathode. J. Phys. Chem. B 108, 17886–17892 (2004).

    Article  CAS  Google Scholar 

  80. Abild-Pedersen, F. & Andersson, M. P. CO adsorption energies on metals with correction for high coordination adsorption sites: a density functional study. Surf. Sci. 601, 1747–1753 (2007).

    Article  CAS  Google Scholar 

  81. Mason, S. E., Grinberg, I. & Rappe, A. M. First-principles extrapolation method for accurate CO adsorption energies on metal surfaces. Phys. Rev. B 69, 161401 (2004).

  82. Chan, K. & Nørskov, J. K. Potential dependence of electrochemical barriers from ab initio calculations. J. Phys. Chem. Lett. 7, 1686–1690 (2016).

    Article  CAS  Google Scholar 

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Acknowledgements

This work was supported by the Rowland Fellows Program at Rowland Institute, Harvard University. H.W. and K.J. acknowledge great support from C. M. Friend at Harvard University. This work was performed in part at the Center for Nanoscale Systems (CNS), a member of the National Nanotechnology Infrastructure Network (NNIN), which is supported by the National Science Foundation under NSF award no. ECS-0335765. CNS is part of Harvard University. Theoretical calculations were based upon work performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the US Department of Energy under award no. DE-SC0004993. This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the US Department of Energy under contract no. DE-AC02-05CH11231.

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  1. Kun Jiang and Robert B. Sandberg contributed equally to this work.

Authors and Affiliations

  1. Rowland Institute, Harvard University, Cambridge, MA, USA

    Kun Jiang & Haotian Wang

  2. SUNCAT Center for Interface Science and Catalysis, Department of Chemical Engineering, Stanford University, Stanford, CA, USA

    Robert B. Sandberg, Xinyan Liu, Jens K. Nørskov & Karen Chan

  3. Center for Nanoscale Systems, Harvard University, Cambridge, MA, USA

    Austin J. Akey & David C. Bell

  4. Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA

    David C. Bell

  5. SUNCAT Center for Interface Science and Catalysis, SLAC National Accelerator Laboratory, Menlo Park, CA, USA

    Jens K. Nørskov & Karen Chan

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Contributions

H.W. designed the experiments of this project. K.C. designed the simulations of this project. K.J. and H.W. performed materials synthesis and catalysis measurements. K.J., A.J.A. and H.W. performed material characterizations. R.B.S., X.L. and K.C. performed simulations. H.W., K.J., K.C., R.B.S. and X.L. wrote the manuscript. K.J., R.B.S., A.J.A., X.L., D.C.B., J.K.N., K.C. and H.W. analysed the results.

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Correspondence to Karen Chan or Haotian Wang.

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Jiang, K., Sandberg, R.B., Akey, A.J. et al. Metal ion cycling of Cu foil for selective C–C coupling in electrochemical CO2 reduction. Nat Catal 1, 111–119 (2018). https://doi.org/10.1038/s41929-017-0009-x

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