Molecular tuning of CO2-to-ethylene conversion

Abstract

The electrocatalytic reduction of carbon dioxide, powered by renewable electricity, to produce valuable fuels and feedstocks provides a sustainable and carbon-neutral approach to the storage of energy produced by intermittent renewable sources1. However, the highly selective generation of economically desirable products such as ethylene from the carbon dioxide reduction reaction (CO2RR) remains a challenge2. Tuning the stabilities of intermediates to favour a desired reaction pathway can improve selectivity3,4,5, and this has recently been explored for the reaction on copper by controlling morphology6, grain boundaries7, facets8, oxidation state9 and dopants10. Unfortunately, the Faradaic efficiency for ethylene is still low in neutral media (60 per cent at a partial current density of 7 milliamperes per square centimetre in the best catalyst reported so far9), resulting in a low energy efficiency. Here we present a molecular tuning strategy—the functionalization of the surface of electrocatalysts with organic molecules—that stabilizes intermediates for more selective CO2RR to ethylene. Using electrochemical, operando/in situ spectroscopic and computational studies, we investigate the influence of a library of molecules, derived by electro-dimerization of arylpyridiniums11, adsorbed on copper. We find that the adhered molecules improve the stabilization of an ‘atop-bound’ CO intermediate (that is, an intermediate bound to a single copper atom), thereby favouring further reduction to ethylene. As a result of this strategy, we report the CO2RR to ethylene with a Faradaic efficiency of 72 per cent at a partial current density of 230 milliamperes per square centimetre in a liquid-electrolyte flow cell in a neutral medium. We report stable ethylene electrosynthesis for 190 hours in a system based on a membrane-electrode assembly that provides a full-cell energy efficiency of 20 per cent. We anticipate that this may be generalized to enable molecular strategies to complement heterogeneous catalysts by stabilizing intermediates through local molecular tuning.

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Fig. 1: Dimerization of N-arylpyridinium additives, and correlation of ethylene selectivity with Bader charge.
Fig. 2: Mechanistic investigations of the stabilization of CO-bound intermediates.
Fig. 3: CO2RR performance in liquid-electrolyte flow cells.
Fig. 4: Ethylene electrosynthesis in a membrane-electrode assembly device.

Data availability

The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.

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Acknowledgements

This work was financially supported by the Ontario Research Fund: Research Excellence Program, the Natural Sciences and Engineering Research Council (NSERC) of Canada, the CIFAR Bio-Inspired Solar Energy program and the Joint Centre of Artificial Synthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the US Department of Energy under award no. DE-SC0004993. All DFT computations were performed on the IBM BlueGene/Q supercomputer with support from the Southern Ontario Smart Computing Innovation Platform (SOSCIP). SOSCIP is funded by the Federal Economic Development Agency of Southern Ontario, the Province of Ontario, IBM Canada Ltd, Ontario Centres of Excellence, Mitacs and 15 Ontario academic member institutions. This research was enabled in part by support provided by Compute Ontario (www.computeontario.ca) and Compute Canada (www.computecanada.ca). This research used synchrotron resources of the Advanced Photon Source (APS), an Office of Science User Facility operated for the US Department of Energy (DOE) Office of Science by Argonne National Laboratory, and was supported by the US DOE under contract no. DE-AC02-06CH11357, and the Canadian Light Source and its funding partners. We thank T. Wu and L. Ma for technical support at 9BM beamline of APS. D.S. acknowledges the NSERC E.W.R. Steacie Memorial Fellowship. A.T. acknowledges Marie Skłodowska-Curie Fellowship H2020-MSCA-IF-2017 (793471). J.L. acknowledges the Banting postdoctoral fellowship. C.M.G. acknowledges NSERC for funding in the form of a postdoctoral fellowship from the government of Canada. J.P.E. thanks NSERC, Hatch and the Government of Ontario for their support through graduate scholarships.

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E.H.S., T.A. and J.C.P. supervised this project. F.L. and Y.L. carried out electrochemical experiments. A.T. and A.R.-H. carried out molecule synthesis and characterizations. Z.W. carried out DFT calculations. C.M.G. and F.L. conducted in situ Raman measurement. F.L. and A.O. carried out the membrane–electrode-assembly experiments. J.L. and F.L. performed XAS measurements. Y.W. carried out scanning electron microscopy and electrochemical impedance spectroscopy measurements. J.P.E. measured the contact angle. C.M. carried out the Comsol modelling. L.T. carried out EPR measurement under the supervision of R.D.B. M.L. performed part of the electrochemical experiments. Z.-Q.L., X.W. and H.L. provided help in NMR analysis. C.M.G., C.P.O. and Y.X. provided help in membrane-electrode assembly measurements. C.-S.T. carried out AFM measurement. D.-H.N. conducted X-ray diffraction measurement. R.Q.-B. carried out X-ray photoelectron spectroscopy measurement. C.T.D., T.T.Z., Y.C.L. and Z.H. provided help in materials synthesis and characterizations. F.L. and E.H.S. wrote the manuscript. All authors discussed the results and assisted during manuscript preparation.

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Correspondence to Theodor Agapie or Jonas C. Peters or Edward H. Sargent.

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The authors declare no competing interests.

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Peer review information Nature thanks Muhyun Baik, Richard I. Masel and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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This file includes Methods, Supplementary Figures 1–34, Supplementary Notes 1–4 and Supplementary Tables 1–5

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Li, F., Thevenon, A., Rosas-Hernández, A. et al. Molecular tuning of CO2-to-ethylene conversion. Nature 577, 509–513 (2020). https://doi.org/10.1038/s41586-019-1782-2

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