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Improving the operational stability of electrochemical CO2 reduction reaction via salt precipitation understanding and management

Nature Energy volume 10, pages 266–277 (2025)Cite this article

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Abstract

The practical application of electrochemical carbon dioxide reduction reaction (CO2RR) technology remains hindered by poor stability, primarily owing to bicarbonate salt formation at the cathode, which blocks reactant CO2 mass flow. Here, using operando characterization tools, we tracked the salt formation process and quantified salt precipitation under varying device operational conditions, elucidating a potential mechanism and optimizing anolyte conditions for long-term (>1,000 h) operation CO2RR to CO under >100 mA cm–2. Liquid droplets carrying cations and (bi)carbonate ions were observed to migrate from the catalyst/membrane interface towards the backside of the gas diffusion electrode, driven by interfacial gas evolution and CO2 flow. These droplets eventually dried, forming bicarbonate salt precipitates that blocked the gas flow channels. On the basis of this observation, we applied a hydrophobic parylene coating to the cathode gas flow channel surface, facilitating the removal of the droplets and extending stability from ~100 h to over 500 h under 200 mA cm–2.

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Fig. 1: Proposed salt formation mechanism in CO2RR MEA electrolysers.
Fig. 2: Mechanistic studies of the salt formation in MEA reactors.
Fig. 3: Mechanistic studies of the cation migration from the catalyst/AEM interface to the backside of the GDE.
Fig. 4: Mechanistic studies of the cation migration from the catalyst/AEM interface to the backside of the GDE.
Fig. 5: CO2RR stability in an MEA electrolyser using different KHCO3 anolyte concentrations at 100 mA cm–2.
Fig. 6: The hydrophobic parylene film coating on the flow channels to remove the KHCO3 droplets.

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The authors declare that all data supporting the findings of this study are available within the paper and Supplementary Information files. Source data are provided with this paper.

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Acknowledgements

This work was supported by the Robert A. Welch Foundation (grant number C-2051-20230405) and the David and Lucile Packard Foundation (grant number 2020-71371). X.S. acknowledges the funding support from the UL Research Institutes, USDA SBIR award (numbers 2022-70012-36900 and 2019-33610-29769), University Training and Research for Fossil Energy Applications (DOE DE-FE-0032092) and DOD DURIP (W911NF-23-1-0320). This work was partially characterized using the facilities at the Shared Equipment Authority (SEA) at Rice University.

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Authors and Affiliations

  1. Department of Chemical and Biomolecular Engineering, Rice University, Houston, TX, USA

    Shaoyun Hao, Ahmad Elgazzar, Tae-Ung Wi, Peng Zhu, Yuge Feng, Yang Xia, Feng-Yang Chen & Haotian Wang

  2. Electrical and Computer Engineering Department, University of Houston, Houston, TX, USA

    Nandakishore Ravi & Xiaonan Shan

  3. Department of Materials Science and Nano Engineering, Rice University, Houston, TX, USA

    Haotian Wang

  4. Department of Chemistry, Rice University, Houston, TX, USA

    Haotian Wang

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  1. Shaoyun Hao
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Contributions

H.W. and S.H. conceived the idea and designed the experiments. H.W. supervised the project. S.H. prepared the samples, performed the experiments and analysed the data. H.W., S.H. and A.E. designed the Raman cell. A.E. assisted with the contact angle measurements, measured the thickness of the parylene and performed the multi-physics modelling. N.R. and X.S. helped perform the operando Raman experiments. T.-U.W. helped perform the TEM characterization. S.H., P.Z., F.-Y.C. and Y.X. did the SEM-EDS characterization. S.H., Y.F. and H.W. designed the schematics. S.H. and H.W. wrote the paper. S.H., A.E. and H.W. revised the paper with inputs from all authors.

Corresponding authors

Correspondence to Xiaonan Shan or Haotian Wang.

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Competing interests

S.H., A.E. and H.W. are listed as inventors on a patent application filed by Rice University that pertains to this work. The other authors declare no competing interests.

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Hao, S., Elgazzar, A., Ravi, N. et al. Improving the operational stability of electrochemical CO2 reduction reaction via salt precipitation understanding and management. Nat Energy 10, 266–277 (2025). https://doi.org/10.1038/s41560-024-01695-4

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