Reverse Water Gas Shift versus Carbon Dioxide Electro-Reduction: The Reaction Pathway Responsible for Carbon Monoxide Production in Solid Oxide Co-Electrolysis Cells

Anders S. Nielsen, Brant A. Peppley and Odne S. Burheim ()
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Anders S. Nielsen: Department of Mechanical and Materials Engineering, Queen’s University, 130 Stuart Street, Kingston, ON K7L 2V9, Canada
Brant A. Peppley: Department of Chemical Engineering, Queen’s University, 19 Division Street, Kingston, ON K7L 2N9, Canada
Odne S. Burheim: Department of Energy and Process Engineering, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway

Energies, 2023, vol. 16, issue 15, 1-9

Abstract: Solid oxide co-electrolysis cells can utilize renewable energy sources for the conversion of steam and carbon dioxide into valuable chemicals and feedstocks. An important challenge in the analysis of these devices is understanding the reaction pathway(s) that govern carbon monoxide generation. Studies in which co-electrolysis polarization lies between those of pure steam and pure carbon dioxide electrolysis suggest that carbon dioxide electro-reduction (CO 2 ER) and the reverse water gas shift (RWGS) reaction are both contributors to CO generation. However, experiments in which co-electrolysis polarization overlaps that of pure steam electrolysis propose that the RWGS reaction dominates CO production and CO 2 ER is negligible. Supported by dimensional analysis, thermodynamics, and reaction kinetics, this work elucidates the reasons for which the latter conclusion is infeasible, and provides evidence for why the observed overlap between co-electrolysis and pure steam electrolysis is a result of the slow kinetics of CO 2 ER in comparison to that of steam, with the RWGS reaction being inconsequential. For sufficiently thin cathode current collectors, we reveal that CO 2 ER is dominant over the RWGS reaction, while the rate of steam electro-reduction is much higher than that of carbon dioxide, which causes the co-electrolysis and pure steam electrolysis polarization curves to overlap. This is contrary to what has been proposed in previous experimental analyses. Ultimately, this work provides insight into how to design solid oxide co-electrolysis cells such that they can exploit a desired reaction pathway in order to improve their efficiency and product selectivity.

Keywords: solid oxide electrolysis cell; solid oxide co-electrolysis; dimensional analysis; thermodynamics; electrochemical kinetics (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2023
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