Abstract
This work reports the design and diagnostic analysis of a pH-neutral CO2-to-CO zero-gap electrolyzer cell incorporating a nickel–nitrogen-doped carbon catalyst. The cell yields ~100% CO faradaic efficiency at applied current densities of up to 250 mA cm−2 at low cell voltage and 40% total energy efficiency. It features a low stoichiometric CO2 excess, λstoich, of 1.2 that yields a molar CO concentration of ~70%vol in the electrolyzer exit stream at 40% single-pass CO2 conversion, with over 100 h stability. Here we introduce the experimental carbon crossover coefficient (CCC) as a tool for electrolyzer cell diagnostics. The CCC describes the ratio between noncatalytic acid–base CO2 consumption and catalytically generated alkalinity, thereby offering insight into the nature of the prevalent ionic transport and transport mechanisms of undesired CO2 losses. We demonstrate the diagnostic value of the CCC in transport-based cell failure during oscillatory cell flooding between salt precipitation and salt redissolution. The present dynamic cell diagnostics provide practical guidelines toward improved CO2 electrolyzer designs.
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Data availability
The data that support the findings of this study are available in the main text and Supplementary Information. Source data are provided with this paper.
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Acknowledgements
The research leading to these results has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement nos. 851441, SELECTCO2, and 101006701, ECOFUEL. This work was financially supported by the Initiative and Networking Fund of the Helmholtz Association (grant agreement no. KA2-HSC-12, ‘A Comprehensive Approach to Harnessing the Innovation Potential of Direct Air Capture and Storage for Reaching CO2-Neutrality’, DACStorE).
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S.B, W.J. and P.S. conceived and designed the project and wrote the paper. Q.F. and W.J. carried out the materials synthesis. S.B. and W.J performed the characterization and electrochemical evaluation. M.K performed the TEM and XPS characterizations. D.G. and A.T. performed the SEM characterization. S.O. performed the BET characterization. All authors read and commented on the paper.
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Nature Chemical Engineering thanks Bingjun Xu and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Extended data
Extended Data Fig. 1 Stability test and analysis of the NiNC cathode.
a) Stability test over 180 h at 100 mA cm-2 and b) Geis measurements of NiNC-IMI at 100 mA cm-2, shown as Nyquist plot. c) CCC analysis over a 180-h stability test.
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Brückner, S., Feng, Q., Ju, W. et al. Design and diagnosis of high-performance CO2-to-CO electrolyzer cells. Nat Chem Eng 1, 229–239 (2024). https://doi.org/10.1038/s44286-024-00035-3
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DOI: https://doi.org/10.1038/s44286-024-00035-3