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A nanoporous capacitive electrochemical ratchet for continuous ion separations

Nature Materials (2026)Cite this article

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Abstract

Directed ion transport in liquid electrolyte solutions underlies many phenomena in natural and industrial settings. While nature has evolved structures that drive continuous ion flow without Faradaic redox reactions, establishing this process in synthetic systems has been challenging. Here we report an ion pump that drives aqueous ions against a force using a capacitive ratchet mechanism independent of redox reactions. Modulation of an electric potential between thin metallic layers on either face of a nanoporous alumina wafer immersed in solution results in persistent voltages and ionic currents. This occurs due to the nonlinear capacitive nature of electric double layers, whose repeated charging and discharging sustains a continuous ion flux. Using this approach, we demonstrate ratchet-driven electrodialysis that reaches a 50% decrease in the conductivity of the solution in a dilution cell. These ratchet-based ion pumps can enable continuous desalination and selective ion separation using an electrically powered device with no moving parts.

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Fig. 1: The RBIP.
Fig. 2: Nonlinear capacitance.
Fig. 3: RBIP performance examination.
Fig. 4: Electrodialysis deionization demonstration.
Fig. 5: Analytical model.

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

References

  1. Kedem, O., Lau, B. & Weiss, E. A. How to drive a flashing electron ratchet to maximize current. Nano Lett. 17, 5848–5854 (2017).

    Article  CAS  PubMed  Google Scholar 

  2. Reimann, P. Brownian motors: noisy transport far from equilibrium. Phys. Rep. 361, 57–265 (2002).

    Article  CAS  Google Scholar 

  3. Astumian, R. D.Stochastically pumped adaptation and directional motion of molecular machines. Proc. Natl Acad. Sci. USA 115, 9405–9413 (2018).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  4. Roeling, E. M. et al. Organic electronic ratchets doing work. Nat. Mater. 10, 51–55 (2011).

    Article  CAS  PubMed  Google Scholar 

  5. Tarlie, M. B. & Astumian, R. D. Optimal modulation of a Brownian ratchet and enhanced sensitivity to a weak external force. Proc. Natl Acad. Sci. USA 95, 2039–2043 (2002).

    Article  Google Scholar 

  6. Parrondo, J. M. R., Blanco, J. M., Cao, F. J. & Brito, R. Efficiency of Brownian motors. Europhys. Lett. 43, 248–254 (1998).

    Article  CAS  Google Scholar 

  7. Kedem, O., Lau, B. & Weiss, E. A. Mechanisms of symmetry breaking in a multidimensional flashing particle ratchet. ACS Nano 11, 7148–7155 (2017).

    Article  CAS  PubMed  Google Scholar 

  8. Kedem, O., Lau, B., Ratner, M. A. & Weiss, E. A. Light-responsive organic flashing electron ratchet. Proc. Natl Acad. Sci. USA 114, 8698–8703 (2017).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  9. Squires, T. M. Induced-charge electrokinetics: fundamental challenges and opportunities. Lab Chip https://doi.org/10.1039/b906909g (2009).

  10. Schwemmer, C., Fringes, S., Duerig, U., Ryu, Y. K. & Knoll, A. W. Experimental observation of current reversal in a rocking Brownian motor. Phys. Rev. Lett. 121, 104102 (2018).

    Article  CAS  PubMed  Google Scholar 

  11. Nicollier, P. et al. Nanometer-scale-resolution multichannel separation of spherical particles in a rocking ratchet with increasing barrier heights. Phys. Rev. Appl. 15, 034006 (2021).

    Article  CAS  Google Scholar 

  12. Skaug, M. J., Schwemmer, C., Fringes, S., Rawlings, C. D. & Knoll, A. W. Nanofluidic rocking Brownian motors. Science 359, 1505–1508 (2018).

    Article  CAS  PubMed  Google Scholar 

  13. Słapik, A., Łuczka, J., Hänggi, P. & Spiechowicz, J. Tunable mass separation via negative mobility. Phys. Rev. Lett. https://doi.org/10.1103/PhysRevLett.122.070602 (2019).

  14. Motz, T., Schmid, G., Hänggi, P., Reguera, D. & Rubí, J. M. Optimizing the performance of the entropic splitter for particle separation. J. Chem. Phys. 141, 074104 (2014).

    Article  CAS  PubMed  Google Scholar 

  15. Reguera, D. et al. Entropic splitter for particle separation. Phys. Rev. Lett. 108, 1–5 (2012).

    Article  Google Scholar 

  16. Yang, B., Long, F. & Mei, D. C. Negative mobility and multiple current reversals induced by colored thermal fluctuation in an asymmetric periodic potential. Eur. Phys. J. B 85, 2–7 (2012).

    Article  Google Scholar 

  17. Siwy, Z. & Fuliński, A. A nanodevice for rectification and pumping ions. Am. J. Phys. 72, 567–574 (2004).

    Article  CAS  Google Scholar 

  18. Siwy, Z. & Fuliński, A. Fabrication of a synthetic nanopore ion pump. Phys. Rev. Lett. 89, 4–7 (2002).

    Article  Google Scholar 

  19. Wu, X., Ramiah Rajasekaran, P. & Martin, C. R. An alternating current electroosmotic pump based on conical nanopore membranes. ACS Nano 10, 4637–4643 (2016).

    Article  CAS  PubMed  Google Scholar 

  20. Herman, A. A. et al. Ratchet-based ion pumps for selective ion separations. PRX Energy 2, 023001 (2023).

    Article  Google Scholar 

  21. Herman, A. & Segev, G. Ambipolar ion pumping with ratchet driven active membranes. Phys. Rev. Appl. 21, 034056 (2024).

    Article  CAS  Google Scholar 

  22. Bazant, M. Z., Thornton, K. & Ajdari, A. Diffuse-charge dynamics in electrochemical systems. Phys. Rev. E 70, 24 (2004).

    Article  Google Scholar 

  23. Kerner, Z. & Pajkossy, T. On the origin of capacitance dispersion of rough electrodes. Electrochim. Acta 46, 207–211 (2000).

    Article  CAS  Google Scholar 

  24. Pajkossy, T. Impedance spectroscopy at interfaces of metals and aqueous solutions—surface roughness, CPE and related issues. Solid State Ion. 176, 1997–2003 (2005).

    Article  CAS  Google Scholar 

  25. Pajkossy, T. Impedance of rough capacitive electrodes. J. Electroanal. Chem. 364, 111–125 (1994).

    Article  CAS  Google Scholar 

  26. Lasia, A. in Modern Aspects of Electrochemistry (eds Conway, B. E. et al.) 143–248 (Springer, 2002); https://doi.org/10.1007/0-306-46916-2_2

  27. White, W., Sanborn, C. D., Fabian, D. M. & Ardo, S. Conversion of visible light into ionic power using photoacid-dye-sensitized bipolar ion-exchange membranes. Joule 2, 1–16 (2017).

    Google Scholar 

  28. Lau, B. & Kedem, O. Electron ratchets: state of the field and future challenges. J. Chem. Phys. 152, 200901 (2020).

    Article  CAS  PubMed  Google Scholar 

  29. Marbach, S., Kavokine, N. & Bocquet, L. Resonant osmosis across active switchable membranes. J. Chem. Phys. 152, 054704 (2020).

    Article  CAS  PubMed  Google Scholar 

  30. Vega, V. et al. Diffusive transport through surface functionalized nanoporous alumina membranes by atomic layer deposition of metal oxides. J. Ind. Eng. Chem. 52, 66–72 (2017).

    Article  CAS  Google Scholar 

Download references

Acknowledgements

R.K. acknowledges the US National Science Foundation Graduate Research Fellowship Program (DGE-1321846). A.H. acknowledges the support of the Boris Mints Institute. E.J.H. acknowledges a Graduate Assistance in Areas of National Need (GAANN) Fellowship. C.M. acknowledges the gracious support for summer research at UC Irvine from Research Corporation for Science Advancement through a Cottrell Scholars Collaborative (award no. 27512) awarded to S.A. and the UCI Vice Provost for Teaching and Learning. Initial conceptualization of the work and initial preliminary results were supported by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the US Department of Energy under award no. DE-SC0004993. F.M.T. acknowledges support from the Helmholtz Association. S.A. acknowledges the support of the Gordon and Betty Moore Foundation under a Moore Inventor Fellowship (GBMF grant no. 5641) and The Beall Family Foundation (UCI Beall Innovation Award). S.A. also acknowledges the Phase I Centers for Chemical Innovation (CCI) Program in the US National Science Foundation Division of Chemistry under Grant CHE-2221599 for supporting collaborative student exchanges with the Sa Group at the University of Massachusetts Boston, as well as revisions to the initial paper submission. G.S. thanks the Azrieli Foundation for financial support within the Azrieli Fellows program. This work is partially funded by the European Union (ERC, ESIP-RM, 101039804). Views and opinions expressed are, however, those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council Executive Agency. Neither the European Union nor the granting authority can be held responsible for them. We also acknowledge R. Penner for allowing us to work with his group members and use their thermal evaporator for the fabrication of some of the RBIPs. We acknowledge the contribution of TAU Nano Center for providing the sputtering and e-beam evaporation equipment, and the high-resolution scanning electron microscopy (HRSEM). We thank G. Radovsky for taking the HRSEM images. We thank O. Nir and A. Chandra for guidance with the electrodialysis set-up.

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Author notes

  1. These authors contributed equally: Rylan Kautz, Alon Herman.

Authors and Affiliations

  1. Department of Materials Science and Engineering, University of California Irvine, Irvine, CA, USA

    Rylan Kautz, Ethan J. Heffernan & Shane Ardo

  2. School of Electrical Engineering, Tel Aviv University, Tel Aviv, Israel

    Alon Herman, Keren Shushan Alshochat, Eden Grossman, Rahul Saxena & Gideon Segev

  3. Department of Chemistry, University of California Irvine, Irvine, CA, USA

    Camila Muñetón & Shane Ardo

  4. Department of Chemistry, University of Massachusetts Boston, Boston, MA, USA

    Camila Muñetón

  5. Chemical Sciences Division, Lawrence Berkeley National Lab, Berkeley, CA, USA

    David Larson, Joel W. Ager III & Francesca M. Toma

  6. Joint Center for Artificial Photosynthesis, Lawrence Berkeley National Lab, Berkeley, CA, USA

    David Larson, Joel W. Ager III & Francesca M. Toma

  7. Materials Sciences Division, Lawrence Berkeley National Lab, Berkeley, CA, USA

    Joel W. Ager III

  8. Department of Materials Science and Engineering, University of California Berkeley, Berkeley, CA, USA

    Joel W. Ager III

  9. Institute of Functional Materials for Sustainability, Helmholtz Zentrum Hereon, Teltow, Germany

    Francesca M. Toma

  10. Faculty of Mechanical and Civil Engineering, Helmut Schmidt University, Hamburg, Germany

    Francesca M. Toma

  11. Department of Chemical and Biomolecular Engineering, University of California Irvine, Irvine, CA, USA

    Shane Ardo

Authors
  1. Rylan Kautz
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Contributions

G.S., J.W.A., F.M.T. and S.A. conceptualized this work, R.K., A.H., E.J.H., K.S.A., E.G., R.S., C.M., D.L. and G.S. conducted the investigation, A.H., S.A. and G.S. designed the methodology, R.K., A.H., E.J.H., K.S.A., R.S., C.M. and G.S. conducted the formal analysis and acquired the data, visualizations were designed by E.J.H., A.H., R.K., S.A. and G.S., the original draft was written by S.A. and G.S., and all authors contributed to its reviewing and editing. G.S. and S.A. supervised the project, while G.S., S.A. and F.M.T. administered it and secured the funding.

Corresponding authors

Correspondence to Shane Ardo or Gideon Segev.

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Competing interests

G.S., J.W.A., F.M.T. and S.A. filed patent applications US 16/907,076 and US 17/125,341 for ratchet-based ion pumping membrane systems. The other authors declare no competing interests.

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Nature Materials thanks the anonymous reviewers for their contribution to the peer review of this work.

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Kautz, R., Herman, A., Heffernan, E.J. et al. A nanoporous capacitive electrochemical ratchet for continuous ion separations. Nat. Mater. (2026). https://doi.org/10.1038/s41563-026-02511-y

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