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Operando cathode activation with alkali metal cations for high current density operation of water-fed zero-gap carbon dioxide electrolysers


Continuous-flow electrolysers allow CO2 reduction at industrially relevant rates, but long-term operation is still challenging. One reason for this is the formation of precipitates in the porous cathode from the alkaline electrolyte and the CO2 feed. Here we show that while precipitate formation is detrimental for the long-term stability, the presence of alkali metal cations at the cathode improves performance. To overcome this contradiction, we develop an operando activation and regeneration process, where the cathode of a zero-gap electrolyser cell is periodically infused with alkali cation-containing solutions. This enables deionized water-fed electrolysers to operate at a CO2 reduction rate matching those using alkaline electrolytes (CO partial current density of 420 ± 50 mA cm−2 for over 200 hours). We deconvolute the complex effects of activation and validate the concept with five different electrolytes and three different commercial membranes. Finally, we demonstrate the scalability of this approach on a multicell electrolyser stack, with an active area of 100 cm2 per cell.

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Fig. 1: Unintended cation cross-over and precipitate formation in alkaline anolyte-fed zero-gap CO2 electrolysers.
Fig. 2: Schematic piping and instrumentation diagram of the test framework employed.
Fig. 3: Cathode activation using different commercially available AEMs.
Fig. 4: Mechanism and reversibility of cathode activation.
Fig. 5: Deconvolution of the complex effect of the activating electrolyte.
Fig. 6: Long-term operation of a CO2 electrolyser with water anolyte and periodic activation.
Fig. 7: Cathode activation experiments in larger electrolyser cells and stack.

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Data availability

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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This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant no. 716539 and 899747, to C.J.). The research was supported by the National Research, Development and Innovation Office (NKFIH) through the FK-132564 project (to E.B.), and by the ‘Széchenyi 2020’ program in the framework of GINOP-2.2.1-15-2017-00041 project (to C.J.). Financial support for purchasing the CT instrument was also provided by NKFIH through the GINOP-2.3.3-15-2016-00010 project (to C.J. and D.S.). This project was supported by the János Bolyai Research Scholarship of the Hungarian Academy of Sciences (to B.E. and D.S.). We thank L. Janovák, Á. Balog, G. F. Samu and G. Bencsik at University of Szeged for assistance in contact angle, SEM–EDX, X-ray diffraction (with Rietveld analysis) and ion chromatography measurements, respectively. We also thank T. Pajkossy (Hungarian Academy of Sciences) for his valuable contribution in the design, analysis and interpretation of EIS measurements. We thank P. Kamat (University of Notre Dame) for critical comments on an earlier version of the manuscript and B. Janáky-Bohner for her support in the preparation of the manuscript.

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Authors and Affiliations



B.E. and C.J. conceived and supervised the project and designed all experiments. A.S. and T.H. prepared the gas diffusion electrodes and assembled the cells. A.S., T.H. and E.K. carried out all electrochemical and product analysis experiments. D.S. performed and analysed micro-CT measurements. B.E., E.K. and C.J. designed the electrodes, the electrochemical cells and the electrolyser system. All authors discussed the results and assisted during manuscript preparation.

Corresponding authors

Correspondence to B. Endrődi or C. Janáky.

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Competing interests

Two patent applications have been filed on the continuous-flow electrolysis of CO2 by some authors of this paper (B.E., A.S., E.K., C.J., all University of Szeged) and their collaborating partner, ThalesNano Zrt. Application numbers: PCT/HU2019/095001 and PCT/HU2020/050033. T.H. and D.S. declare no competing interests.

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Supplementary information

Supplementary Information

Supplementary Notes 1–8 and Figs. 1–24.

Supplementary Data 1

Source data for figures in the Supplementary Information.

Source data

Source Data Fig. 3a

Raw data for contact angle measurements.

Source Data Fig. 5

Raw partial current density data.

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Endrődi, B., Samu, A., Kecsenovity, E. et al. Operando cathode activation with alkali metal cations for high current density operation of water-fed zero-gap carbon dioxide electrolysers. Nat Energy 6, 439–448 (2021).

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