The electrochemical reduction of CO2 to valuable C2+ feedstocks is hindered by the competitive formation of C1 products and H2 evolution. Here we tuned the H2O thermodynamic activity between 0.97 and 0.47 using water-in-salt electrolytes to obtain mechanistic insights into the role of H2O in controlling C–C coupling versus C1 product formation on Cu electrodes. By lowering the thermodynamic H2O activity to 0.66, we obtained a Faradaic efficiency of ~73% at a partial current density of −110 mA cm−2 for C2+ products, at modest overpotentials. The adjustment of the thermodynamic H2O activity provided fine control over C2+/C1 ratios, spanning a range from 1 to 20. The trends support the pivotal role of the thermodynamic H2O activity in increasing the CO surface coverages and promoting C–C coupling to C2 products. These findings highlight the potential of tuning thermodynamic H2O activity as a guiding principle to maximize CO2 reduction into highly desirable C2+ products.
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All data are available in the figshare repository at https://doi.org/10.6084/m9.figshare.23692962 or from the corresponding author upon reasonable request.
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A.S.H. acknowledges financial support from the National Science Foundation under award no. CHE-2102648. H.Z. acknowledges the support from the National Science Foundation Graduate Research Fellowship under grant No. 2139757. Certain equipment, instruments, software or materials, commercial or non-commercial, are identified in this paper to specify the experimental procedure adequately. Such identification is not intended to imply recommendation or endorsement of any product or service by the National Institute of Standards and Technology, nor is it intended to imply that the materials or equipment identified are necessarily the best available for the purpose.
H.Z., J.G. and A.S.H. and their institutions have filed a US provisional patent application titled ‘Controlling water activity to promote selective electrochemical reactions’ (63/439,498). D.R. declares no competing interests.
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Zhang, H., Gao, J., Raciti, D. et al. Promoting Cu-catalysed CO2 electroreduction to multicarbon products by tuning the activity of H2O. Nat Catal 6, 807–817 (2023). https://doi.org/10.1038/s41929-023-01010-6
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