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Improving the efficiency of CO2 electrolysis by using a bipolar membrane with a weak-acid cation exchange layer

Nature Chemistry volume 13, pages 33–40 (2021)Cite this article

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Abstract

The efficient conversion of electricity to chemicals is needed to mitigate the intermittency of renewable energy sources. Driving these electrochemical conversions at useful rates requires not only fast electrode kinetics, but also rapid mass and ion transport. However, little is known about the effect of local environments on ionic flows in solid polymer electrolytes. Here, we show that it is possible to measure and manipulate the local pH in membrane electrolysers with a resolution of tens of nanometres. In bipolar-membrane-based gas-fed CO2 electrolysers, the acidic environment of the cation exchange layer results in low CO2 reduction efficiency. By using ratiometric indicators and layer-by-layer polyelectrolyte assembly, the local pH was measured and controlled within an ~50-nm-thick weak-acid layer. The weak-acid layer suppressed the competing hydrogen evolution reaction without affecting CO2 reduction. This method of probing and controlling the local membrane environment may be useful in devices such as electrolysers, fuel cells and flow batteries, as well as in operando studies of ion distributions within polymer electrolytes.

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Fig. 1: An acidic cathode environment leads to low FE for CO2 reduction in a BPM-based electrolyser.
Fig. 2: Modification of the BPM by LBL assembly.
Fig. 3: Attaching pH-responsive dyes to PAH and pH calibration.
Fig. 4: Measurement of the local pH in the LBL film on the modified BPM.
Fig. 5: Electrochemical properties of the LBL-modified BPM and Nafion BPM.

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The datasets generated during and/or analysed during the current study are included in this paper and its Supplementary Information and Source Data files. Source data are provided with this paper.

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Acknowledgements

Z.Y. thanks L. Ren for assisting with sample preparation. This work was supported by the Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Energy Bioscience, Department of Energy (contract no. SC-0019781) and by the Canadian Institute for Advanced Research. J.L.H. acknowledges support as a graduate fellow of the Vagelos Institute for Energy Science and Technology at the University of Pennsylvania. Anion exchange membrane synthesis was supported by the DOE-NETL University Coalition for Fossil Energy Research (UCFER) (grant no. DE-FE0026825, subaward 0001-PSU-DOE-6825).

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Authors and Affiliations

  1. Department of Chemistry, University of Pennsylvania, Philadelphia, PA, USA

    Zhifei Yan, Jeremy L. Hitt, Zichen Zeng & Thomas E. Mallouk

  2. Department of Materials Science and Engineering, Department of Chemistry, Pennsylvania State University, Philadelphia, PA, USA

    Michael A. Hickner

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Contributions

Z.Y., M.A.H. and T.E.M. designed the study. Z.Y. carried out the experimental work with assistance from J.L.H. and Z.Z. Z.Y. and T.E.M. drafted the manuscript, which was reviewed and edited by all authors.

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Correspondence to Thomas E. Mallouk.

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Supplementary Figs. 1–14 and Discussion.

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Yan, Z., Hitt, J.L., Zeng, Z. et al. Improving the efficiency of CO2 electrolysis by using a bipolar membrane with a weak-acid cation exchange layer. Nat. Chem. 13, 33–40 (2021). https://doi.org/10.1038/s41557-020-00602-0

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