Abstract
Ion-solvating membranes (ISMs) are an alternative to proton-exchange and anion-exchange membranes for use in water electrolysers. ISMs do not have fixed ionic groups in their structure but instead gain their ionic conductivity through the uptake of liquid electrolyte. Although in principle they could offer improved stability over anion-exchange membranes due to the absence of easily degradable anion-exchange groups, stability gains have been modest. Here we report poly(oxindole biphenylene)-based ISMs with highly stable oxindole/KOH complex ion pairs for use in water electrolysers. These ISMs exhibit promising alkaline stability at 80 °C with a negligible conductivity decay over more than 15,000 h and, thus, allow durable alkaline electrolysis over 2,500 h, even at elevated temperatures and high operating voltages of 2.3 V. Moreover, they show ultralow gas permeation and, thus, low transient response times (<1 s). They allow the use of non-precious-metal catalysts (Ni and Ni/Fe) and can be operated over a broad temperature range (−35 to 120 °C).
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Data availability
The authors declare that the data supporting the findings of this study are available within the paper, Supplementary Information and Source Data files. Further data beyond the immediate results presented here are available from the corresponding authors upon reasonable request. Source data are provided with this paper.
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Acknowledgements
We thank X. Zhang from Nanjing University of Science and Technology for the simulations and M. Dou at the Institute of Coal Chemistry of the Chinese Academy of Sciences for help with the NMR. We also thank Shiyanjia Lab (www.shiyanjia.com) for support during the DFT test. Financial support for this work was provided by the National Natural Science Foundation of China (Grant Nos. 21835005 and 22105217), the STS Project of the Chinese Academy of Sciences (Grant No. KFJ-STS-QYZD-2021-02-003) and the Natural Science Foundation of Shanxi Province (Grant No. 20210302124433).
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N.L. initiated this collaborative project. K.G. helped with data collection and the formal analysis. X.H. synthesized the polymeric materials, designed the experiments and wrote the original draft of the manuscript. C.N. and J.Y. set up the testing system at high operating pressure and high temperature and collected the data. K.G., B.H., M.L., H.T. and S.K. characterized the electrolyser tests and reviewed the draft of the manuscript. Y.H., N.L. and K.G. contributed to the writing of the manuscript. K.G. and N.L. supervised and guided the work.
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Nature Energy thanks Patric Jannasch, Jens Oluf Jensen and Yu Seung Kim for their contribution to the peer review of this work.
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Supplementary information
Supplementary Information
Supplementary Figs. 1–3 show the alkaline stability of a small molecule. Supplementary Fig. 4 shows the dynamic thermomechanical analysis of POBP. Supplementary Figs. 5–14 show the swelling behaviour, XRD, structure and hydrophily of all the POBPs. Supplementary Figs. 15 and 16 show the thermal stability of POBP. Supplementary Figs. 17–19 show the alkaline and oxidative stability of POBP. Supplementary Figs. 20–28 show the AWE device performance of POBP. Supplementary Figs. 29–35 show the in situ stability of POBP under different conditionals. Supplementary Table 1 lists the solubility of the POBP and Supplementary Table 2 lists the polymerization conditions of the POBP.
Supplementary Data 1
Source Data for Supplementary Figs. 1–35.
Source data
Source Data for Fig. 1
DFT calculation and alkaline stability test of model compounds.
Source Data for Fig. 2
Preparation, composition, mechanical properties and gas permeability characterization of POBP-ISMs.
Source Data for Fig. 3
Ion conductivity, alkaline durability, oxidation stability of POBP and 1H NMR spectra of pristine and aged POBP after alkaline during test and Fenton test.
Source Data for Fig. 4
Polarization curves of POBP-ISM AWE under different conditions and area resistance (AR).
Source Data for Fig. 5
In situ durability of electrolyser with POBP-ISMs at 80 °C and comparison of in situ durability and cell voltage of present POBP-ISM and current ISMs and AEMs.
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Hu, X., Hu, B., Niu, C. et al. An operationally broadened alkaline water electrolyser enabled by highly stable poly(oxindole biphenylene) ion-solvating membranes. Nat Energy 9, 401–410 (2024). https://doi.org/10.1038/s41560-023-01447-w
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DOI: https://doi.org/10.1038/s41560-023-01447-w