Abstract
Specifically adsorbed alkali metal cations on metal electrodes have been hypothesized to influence the reduction of CO2. However, experimental detection of these cations during CO2 reduction remains elusive. Herein, employing the asymmetric CH3 deformation band of tetramethylammonium as a vibrational probe of the aqueous electrolyte–polycrystalline Au interface, we monitored the displacement of specifically adsorbed tetramethylammonium by alkali metal cations. We found that the coverage of specifically adsorbed alkali metal cations during CO2-to-CO reduction follows the order Li+ < Na+ < K+ < Cs+ for the same bulk concentration. The alkali metal cations’ experimentally observed surface coverages correlate with their free energies of hydration. Furthermore, the rate of CO2-to-CO conversion increases with the coverage of specifically adsorbed alkali metal cations. Our observations suggest that the degree to which alkali metal cations undergo partial dehydration at the electrode–electrolyte interface plays a key role in their ability to promote CO2-to-CO reduction.
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Data availability
Representative data and extended datasets that support the findings reported in this study are available in the manuscript and the Supplementary Information. The data in the figures shown in the main text and DFT-calculated coordinates for the optimized geometries of the cations on Au(111) are provided in machine-readable formats as supplementary files. Additional data are available from the corresponding authors upon reasonable request.
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Acknowledgements
This work was supported by a CAREER award (to M.M.W.) from the National Science Foundation (no. CHE-1847841). N.A. and M.J.J. acknowledge the National Science Foundation for support (award no. CHE-1665155).
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All authors discussed the results and commented on and revised the manuscript. M.M.W. and V.J.O. conceived and designed the experiments. V.J.O. conducted the experiments. Y.-S.H. participated in data collection. M.J.J. and N.A. contributed the DFT work.
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Nature Catalysis thanks Yanwei Lum, Wenbin Cai and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Supplementary Figs. 1–11, Tables 1–4 and Notes 1 and 2.
Supplementary Data 1
Coordinates for optimized geometries of cations on Au(111).
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Machine-readable data shown in Figs. 1–7.
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Ovalle, V.J., Hsu, YS., Agrawal, N. et al. Correlating hydration free energy and specific adsorption of alkali metal cations during CO2 electroreduction on Au. Nat Catal 5, 624–632 (2022). https://doi.org/10.1038/s41929-022-00816-0
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DOI: https://doi.org/10.1038/s41929-022-00816-0
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