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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.

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.


  1. Hepburn, C. et al. The technological and economic prospects for CO2 utilization and removal. Nature 575, 87–97 (2019).

    Google Scholar 

  2. Endrődi, B. et al. Continuous-flow electroreduction of carbon dioxide. Prog. Energy Combust. Sci. 62, 133–154 (2017).

    Google Scholar 

  3. Weekes, D. M., Salvatore, D. A., Reyes, A., Huang, A. & Berlinguette, C. P. Electrolytic CO2 reduction in a flow cell. Acc. Chem. Res. 51, 910–918 (2018).

    Google Scholar 

  4. De Luna, P. et al. What would it take for renewably powered electrosynthesis to displace petrochemical processes? Science 364, eaav3506 (2019).

    Google Scholar 

  5. He, J. & Janáky, C. Recent advances in solar-driven carbon dioxide conversion: expectations versus reality. ACS Energy Lett. 5, 1996–2014 (2020).

    Google Scholar 

  6. Jouny, M., Luc, W. & Jiao, F. General techno-economic analysis of CO2 electrolysis systems. Ind. Eng. Chem. Res. 57, 2165–2177 (2018).

    Google Scholar 

  7. Verma, S. et al. A gross-margin model for defining technoeconomic benchmarks in the electroreduction of CO2. ChemSusChem 9, 1972–1979 (2016).

    Google Scholar 

  8. Schreier, M. et al. Solar conversion of CO2 to CO using Earth-abundant electrocatalysts prepared by atomic layer modification of CuO. Nat. Energy 2, 17087 (2017).

    Google Scholar 

  9. Arán-Ais, R. M., Scholten, F., Kunze, S., Rizo, R. & Roldan Cuenya, B. The role of in situ generated morphological motifs and Cu(i) species in C2+ product selectivity during CO2 pulsed electroreduction. Nat. Energy 5, 317–325 (2020).

    Google Scholar 

  10. Endrődi, B. et al. High carbonate ion conductance of a robust PiperION membrane allows industrial current density and conversion in a zero-gap carbon dioxide electrolyzer cell. Energy Environ. Sci. 13, 4098–4105 (2020).

    Google Scholar 

  11. Liu, K., Smith, W. A. & Burdyny, T. Introductory guide to assembling and operating gas diffusion electrodes for electrochemical CO2 reduction. ACS Energy Lett. 4, 639–643 (2019).

    Google Scholar 

  12. Burdyny, T. & Smith, W. A. CO2 reduction on gas-diffusion electrodes and why catalytic performance must be assessed at commercially-relevant conditions. Energy Environ. Sci. 12, 1442–1453 (2019).

    Google Scholar 

  13. Bhargava, S. S. et al. System design rules for intensifying the electrochemical reduction of CO2 to CO on Ag nanoparticles. ChemElectroChem 7, 2001–2011 (2020).

    Google Scholar 

  14. Kibria, M. G. et al. A surface reconstruction route to high productivity and selectivity in CO2 electroreduction toward C2+ hydrocarbons. Adv. Mater. 30, 1804867 (2018).

    Google Scholar 

  15. Ma, W. et al. Electrocatalytic reduction of CO2 to ethylene and ethanol through hydrogen-assisted C–C coupling over fluorine-modified copper. Nat. Catal. 3, 478–487 (2020).

    Google Scholar 

  16. De Gregorio, G. L. et al. Facet-dependent selectivity of Cu catalysts in electrochemical CO2 reduction at commercially viable current densities. ACS Catal. 10, 4854–4862 (2020).

    Google Scholar 

  17. Wang, X. et al. Efficient methane electrosynthesis enabled by tuning local CO2 availability. J. Am. Chem. Soc. 142, 3525–3531 (2020).

    Google Scholar 

  18. García de Arquer, F. P. et al. CO2 electrolysis to multicarbon products at activities greater than 1 A cm−2. Science 367, 661–666 (2020).

    Google Scholar 

  19. Verma, S., Lu, S. & Kenis, P. J. A. Co-electrolysis of CO2 and glycerol as a pathway to carbon chemicals with improved technoeconomics due to low electricity consumption. Nat. Energy 4, 466–474 (2019).

    Google Scholar 

  20. Na, J. et al. General technoeconomic analysis for electrochemical coproduction coupling carbon dioxide reduction with organic oxidation. Nat. Commun. 10, 5193 (2019).

    Google Scholar 

  21. Vass, Á., Endrődi, B. & Janáky, C. Coupling electrochemical carbon dioxide conversion with value-added anode processes: an emerging paradigm. Curr. Opin. Electrochem. 25, 100621 (2021).

    Google Scholar 

  22. Larrazábal, G. O. et al. Analysis of mass flows and membrane cross-over in CO2 reduction at high current densities in an MEA-type electrolyzer. ACS Appl. Mater. Interfaces 11, 41281–41288 (2019).

    Google Scholar 

  23. Ma, M. et al. Insights into the carbon balance for CO2 electroreduction on Cu using gas diffusion electrode reactor designs. Energy Environ. Sci. 13, 977–985 (2020).

    Google Scholar 

  24. Endrödi, B. et al. Multilayer electrolyzer stack converts carbon dioxide to gas products at high pressure with high efficiency. ACS Energy Lett. 4, 1770–1777 (2019).

    Google Scholar 

  25. Wang, R. et al. Maximizing Ag utilization in high-rate CO2 electrochemical reduction with a coordination polymer-mediated gas diffusion electrode. ACS Energy Lett. 4, 2024–2031 (2019).

    Google Scholar 

  26. Kaczur, J. J., Yang, H., Liu, Z., Sajjad, S. D. & Masel, R. I. A review of the use of immobilized ionic liquids in the electrochemical conversion of CO2. J. Carbon Res. 6, 33 (2020).

    Google Scholar 

  27. Yin, Z. et al. An alkaline polymer electrolyte CO2 electrolyzer operated with pure water. Energy Environ. Sci. 12, 2455–2462 (2019).

    Google Scholar 

  28. Gabardo, C. M. et al. Combined high alkalinity and pressurization enable efficient CO2 electroreduction to CO. Energy Environ. Sci. 11, 2531–2539 (2018).

    Google Scholar 

  29. Wheeler, D. G. et al. Quantification of water transport in a CO2 electrolyzer. Energy Environ. Sci. 13, 5126–5134 (2020).

    Google Scholar 

  30. Zhao, C., Chen, X. & Zhao, C. Carbonation behavior of K2CO3 with different microstructure used as an active component of dry sorbents for CO2 capture. Ind. Eng. Chem. Res. 49, 12212–12216 (2010).

    Google Scholar 

  31. Chioyama, H., Luo, H., Ohba, T. & Kanoh, H. Temperature-dependent double-step CO2 occlusion of K2CO3 under moist conditions. Adsorpt. Sci. Technol. 33, 243–250 (2015).

    Google Scholar 

  32. Verma, S. et al. Insights into the low overpotential electroreduction of CO2 to CO on a supported gold catalyst in an alkaline flow electrolyzer. ACS Energy Lett. 3, 193–198 (2018).

    Google Scholar 

  33. Kudo, Y. et al. Carbon dioxide electrolytic device and carbon dioxide electrolytic method. US patent 20180274109A1 (2018).

  34. Leonard, M. E., Clarke, L. E., Forner‐Cuenca, A., Brown, S. M. & Brushett, F. R. Investigating electrode flooding in a flowing electrolyte, gas‐fed carbon dioxide electrolyzer. ChemSusChem 13, 400–411 (2020).

    Google Scholar 

  35. Liu, Z., Yang, H., Kutz, R. & Masel, R. I. CO2 electrolysis to CO and O2 at high selectivity, stability and efficiency using sustainion membranes. J. Electrochem. Soc. 165, J3371–J3377 (2018).

    Google Scholar 

  36. Luo, X., Rojas-Carbonell, S., Yan, Y. & Kusoglu, A. Structure-transport relationships of poly(aryl piperidinium) anion-exchange membranes: effect of anions and hydration. J. Memb. Sci. 598, 117680 (2020).

    Google Scholar 

  37. Ringe, S. et al. Understanding cation effects in electrochemical CO2 reduction. Energy Environ. Sci. 12, 3001–3014 (2019).

    Google Scholar 

  38. Resasco, J. et al. Promoter effects of alkali metal cations on the electrochemical reduction of carbon dioxide. J. Am. Chem. Soc. 139, 11277–11287 (2017).

    Google Scholar 

  39. Lobaccaro, P. et al. Effects of temperature and gas–liquid mass transfer on the operation of small electrochemical cells for the quantitative evaluation of CO2 reduction electrocatalysts. Phys. Chem. Chem. Phys. 18, 26777–26785 (2016).

    Google Scholar 

  40. Pérez-Gallent, E., Marcandalli, G., Figueiredo, M. C., Calle-Vallejo, F. & Koper, M. T. M. Structure- and potential-dependent cation effects on CO reduction at copper single-crystal electrodes. J. Am. Chem. Soc. 139, 16412–16419 (2017).

    Google Scholar 

  41. Chen, L. D., Urushihara, M., Chan, K. & Nørskov, J. K. Electric field effects in electrochemical CO2 reduction. ACS Catal. 6, 7133–7139 (2016).

    Google Scholar 

  42. Birdja, Y. Y. et al. Advances and challenges in understanding the electrocatalytic conversion of carbon dioxide to fuels. Nat. Energy 4, 732–745 (2019).

    Google Scholar 

  43. Murata, A. & Hori, Y. Product selectivity affected by cationic species in electrochemical reduction of CO2 and CO at a Cu electrode. Bull. Chem. Soc. Jpn 64, 123–127 (1991).

    Google Scholar 

  44. Singh, M. R., Kwon, Y., Lum, Y., Ager, J. W. & Bell, A. T. Hydrolysis of electrolyte cations enhances the electrochemical reduction of CO2 over Ag and Cu. J. Am. Chem. Soc. 138, 13006–13012 (2016).

    Google Scholar 

  45. Thorson, M. R., Siil, K. I. & Kenis, P. J. A. Effect of cations on the electrochemical conversion of CO2 to CO. J. Electrochem. Soc. 160, F69–F74 (2013).

    Google Scholar 

  46. Carmo, M., Fritz, D. L., Mergel, J. & Stolten, D. A comprehensive review on PEM water electrolysis. Int. J. Hydrog. Energy 38, 4901–4934 (2013).

    Google Scholar 

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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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