Negative dielectric constant of water confined in nanosheets

Akira Sugahara, Yasunobu Ando, Satoshi Kajiyama, Koji Yazawa, Kazuma Gotoh, Minoru Otani, Masashi Okubo, Atsuo Yamada*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

101 Citations (Scopus)


Electric double-layer capacitors are efficient energy storage devices that have the potential to account for uneven power demand in sustainable energy systems. Earlier attempts to improve an unsatisfactory capacitance of electric double-layer capacitors have focused on meso- or nanostructuring to increase the accessible surface area and minimize the distance between the adsorbed ions and the electrode. However, the dielectric constant of the electrolyte solvent embedded between adsorbed ions and the electrode surface, which also governs the capacitance, has not been previously exploited to manipulate the capacitance. Here we show that the capacitance of electric double-layer capacitor electrodes can be enlarged when the water molecules are strongly confined into the two-dimensional slits of titanium carbide MXene nanosheets. Using electrochemical methods and theoretical modeling, we find that dipolar polarization of strongly confined water resonantly overscreens an external electric field and enhances capacitance with a characteristically negative dielectric constant of a water molecule.

Original languageEnglish
Article number850
JournalNature communications
Issue number1
Publication statusPublished - 2019 Dec 1
Externally publishedYes

ASJC Scopus subject areas

  • Chemistry(all)
  • Biochemistry, Genetics and Molecular Biology(all)
  • Physics and Astronomy(all)


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