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Direct air capture of CO2 in an electrochemical hybrid flow cell with a spatially isolated phenazine electrode

Nature Energy volume 10, pages 1146–1154 (2025)Cite this article

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Abstract

CO2 capture based on a pH swing driven electrically through the reversible proton-coupled electron transfer of organic molecules could be powered entirely by clean electricity. A major technical challenge is the reversible chemical oxidation of the reduced organics by atmospheric O2, which can lower energy efficiency and capture capacity. Here we report the development of a hybrid phenazine flow cell system that uses a pH-swing direct air capture (DAC) process, utilizing redox-active cyclic poly(phenazine sulfide) fabricated solid electrodes. The system maintains a separation between the air and the O2-sensitive reduced phenazine, enabling stable and effective CO2 capture from gas mixtures containing O2. This flow cell demonstrated substantial oxygen compatibility, exhibiting a coulombic efficiency of 99% and requiring only 73 kJ mol−1 CO2 for simulated flue gas and 104 kJ mol−1 CO2 for DAC. The strategy of isolating vulnerable species offers an efficient pathway for DAC and may be broadly applicable to avoiding undesirable side reactions in other electrochemical devices.

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Fig. 1: Schematic of the hybrid flow carbon capture set-up.
Fig. 2: Characterization of the CPS-CNT electrode and rate performance of the CPS-CNT flow cell.
Fig. 3: Schematic of the CO2 capture–release system and two typical CO2-concentrating cycles.
Fig. 4: CO2 capture performance at different conditions.

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All data supporting the findings of this study are available within the article and its Supplementary Information. Source data are provided with this paper.

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Acknowledgements

We thank Y. Tang from Shanghai Institute of Organic Chemistry for helpful discussions. Financial support received from National Natural Science Foundation of China (grant nos. 22422803, 22101064 and 22375167), the open research fund of Suzhou Laboratory (grant no. SZLAB-1308-2024-TS008), the National Key R&D Program of China (grant nos. 2022YFB2405100 and 2022YFB2405000), the Research Funds of Hangzhou Institute for Advanced Study, UCAS (grant no. 2023HIAS-Y018) and Zhejiang Provincial Natural Science Foundation of China (XHD24B0501) is gratefully acknowledged. Research at Harvard University was supported by the Harvard University Climate Change Solutions Fund. We thank the Instrumentation and Service Center for Physical Science at Westlake University for the facility support and technical assistance.

Author information

Author notes

  1. These authors contributed equally: Xinyu Jin, Shijian Jin.

Authors and Affiliations

  1. School of Chemistry and Materials Science, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, Hangzhou, China

    Xinyu Jin & Yunlong Ji

  2. John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA

    Shijian Jin, Roy G. Gordon & Michael J. Aziz

  3. Key Laboratory of Precise Synthesis of Functional Molecules of Zhejiang Province, Department of Chemistry, School of Science, Westlake University, Hangzhou, China

    Lu Li & Pan Wang

  4. Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA

    Roy G. Gordon

Authors
  1. Xinyu Jin
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Contributions

Y.J., M.J.A., P.W. and R.G.G. formulated and supervised the project. X.J. and L.L. synthesized the compounds. X.J. performed the CO2 capture tests. S.J. performed the theoretical analysis. S.J., Y.J., P.W. and M.J.A. wrote the paper, and all authors contributed to revising the paper.

Corresponding authors

Correspondence to Pan Wang, Michael J. Aziz or Yunlong Ji.

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Competing interests

A patent application (CN202410616404.7) has been filed by Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, with Y.J., P.W. and X.J. as inventors.

Peer review

Peer review information

Nature Energy thanks Seoni Kim, Kangkang Li and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–51, Tables 1 and 2 and Notes 1–6.

Source data

Source Data Fig. 3

Source data for the CO2 capture–release system and two typical CO2-concentrating cycles.

Source Data Fig. 4

Source data for the CO2 capture performance at different conditions.

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Jin, X., Jin, S., Li, L. et al. Direct air capture of CO2 in an electrochemical hybrid flow cell with a spatially isolated phenazine electrode. Nat Energy 10, 1146–1154 (2025). https://doi.org/10.1038/s41560-025-01836-3

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