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Unified mechanistic understanding of CO2 reduction to CO on transition metal and single atom catalysts

Nature Catalysis volume 4, pages 1024–1031 (2021)Cite this article

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Abstract

CO is the simplest product from CO2 electroreduction (CO2R), but the identity and nature of its rate-limiting step remain controversial. Here we investigate the activity of transition metals (TMs), metal–nitrogen-doped carbon catalysts (MNCs) and a supported phthalocyanine, and present a unified mechanistic picture of the CO2R to CO for these catalysts. Applying the Newns–Andersen model, we find that on MNCs, like TMs, electron transfer to CO2 is facile. We find CO2* adsorption to generally be limiting on TMs, whereas MNCs can be limited by either CO2* adsorption or by the proton–electron transfer reaction to form COOH*. We evaluate these computed mechanisms against pH-dependent experimental activity measurements on the CO2R to CO activity. We present a unified activity volcano that includes the decisive CO2* and COOH* binding strengths. We show that the increased activity of MNC catalysts is due to the stabilization of larger adsorbate dipoles, which results from their discrete and narrow d states.

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Fig. 1: Rate of electron transfer on MNC ≈ 1014 s–1.
Fig. 2: Both CO2* adsorption and COOH* formation can be rate limiting.
Fig. 3: General activity volcano for CO2R to CO.
Fig. 4: Narrow d states stabilize larger dipoles.

Data availability

All computational data, which include the adsorption energies of CO2, COOH and CO, optimized atomic coordinates, data for plotting density of states and microkinetic analysis are available at https://doi.org/10.24435/materialscloud:ws-7t.

Code availability

Python analysis scripts to reproduce all the figures in the manuscript are available at https://github.com/CatTheoryDTU/kinetic-modelling-CO2R.

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Acknowledgements

The research leading to these results received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement no. 851441, SELECTCO2, and from the VILLUM Centre for the Science of Sustainable Fuels and Chemicals (no. 9455) from VILLUM FONDEN. Research leading to some of these results received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement no. 779366, CRESCENDO. The authors acknowledge computational resource from PRACE (project ID: prpa85) and the Juelich Supercomputing Centre. We thank G. Kastlunger for helpful discussions.

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  1. These authors contributed equally: Sudarshan Vijay and Wen Ju.

  2. These authors jointly supervised: Peter Strasser and Karen Chan.

Authors and Affiliations

  1. CatTheory, Department of Physics, Technical University of Denmark, Lyngby, Denmark

    Sudarshan Vijay, Sze-Chun Tsang & Karen Chan

  2. Department of Chemistry, Chemical Engineering Division, Technical University Berlin, Berlin, Germany

    Wen Ju, Sven Brückner & Peter Strasser

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  1. Sudarshan Vijay
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Contributions

S.V. and K.C. designed the computational study and wrote the first draft of the paper. S.V. and S.-C.T. performed the DFT calculations and the data analysis. P.S. designed the experiments, and W.J. and S.B. performed them. All the authors contributed to revising the manuscript.

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Correspondence to Peter Strasser or Karen Chan.

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Vijay, S., Ju, W., Brückner, S. et al. Unified mechanistic understanding of CO2 reduction to CO on transition metal and single atom catalysts. Nat Catal 4, 1024–1031 (2021). https://doi.org/10.1038/s41929-021-00705-y

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