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Direct observation of water-mediated single-proton transport between hBN surface defects

Abstract

Aqueous proton transport at interfaces is ubiquitous and crucial for a number of fields, ranging from cellular transport and signalling, to catalysis and membrane science. However, due to their light mass, small size and high chemical reactivity, uncovering the surface transport of single protons at room temperature and in an aqueous environment has so far remained out-of-reach of conventional atomic-scale surface science techniques, such as scanning tunnelling microscopy. Here, we use single-molecule localization microscopy to resolve optically the transport of individual excess protons at the interface of hexagonal boron nitride crystals and aqueous solutions at room temperature. Single excess proton trajectories are revealed by the successive protonation and activation of optically active defects at the surface of the crystal. Our observations demonstrate, at the single-molecule scale, that the solid/water interface provides a preferential pathway for lateral proton transport, with broad implications for molecular charge transport at liquid interfaces.

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Fig. 1: Reactivity of hBN defects in aqueous conditions: protonation activates defects.
Fig. 2: Luminescence migration reveals proton trajectories.
Fig. 3: Large-scale mapping of proton trajectories.
Fig. 4: Mobility and segregation of protons at interfaces.

Data availability

The data that support the findings of this study are available from the corresponding authors on reasonable request.

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Acknowledgements

J.C. acknowledges valuable discussions with A. Descloux and V. Navikas. This work was financially supported by the Swiss National Science Foundation Consolidator grant (BIONIC BSCGI0_157802) and CCMX project (Large area growth of 2D materials for device integration). E.G. acknowledges support from the Swiss National Science Foundation through the National Centre of Competence in Research Bio-Inspired Materials. The quantum simulation work was performed on the French national supercomputer Occigen under DARI grants A0030807364 and A0030802309. M.-L.B. acknowledges funding from ANR project Neptune. K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by MEXT, Japan, and CREST (JPMJCR15F3), JST.

Author information

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Authors

Contributions

J.C. and A.R. conceived and designed the experiments and J.C. performed the experiments with help from E.G. and A.A. J.C. analysed data and wrote the paper, with input from all authors. B.G. carried out simulations, with help from R.V. and M.-L.B, and K.W. and T.T. contributed materials. A.R. supervised the project. All authors discussed the results and commented on the manuscript.

Corresponding authors

Correspondence to Jean Comtet or Aleksandra Radenovic.

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The authors declare no competing interests.

Additional information

Peer review information Nature Nanotechnology thanks Johan Hofkens, Peter Pohl and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–31, Discussions 1–5 and refs. 1–29.

Supplementary Video 1

Protonation of VB- by H2O. Hydrogen, boron, nitrogen and oxygen atoms are respectively represented in white, blue, green and red while the reactive aqueous species is displayed in cyan.

Supplementary Video 2

Wide-field movie of the flake shown in Fig. 3. Movies are slowed down 5 times (10 frames per second, with 20 ms sampling time). Red circles show positions of localized defects. Circles have 300 nm radius.

Supplementary Video 3

Luminescence trajectory of Fig. 2. Scale bar is 500 nm.

Supplementary Video 4

Luminescence trajectory of Fig. 3a.

Supplementary Video 5

Luminescence trajectory of Fig. 3c.

Supplementary Video 6

Luminescence trajectory of Fig. 3b.

Supplementary Video 7

Luminescence trajectory of Fig. S19A.

Supplementary Video 8

Luminescence trajectory of Fig. S19B.

Supplementary Video 9

Non-biased trajectory of hydronium ion physisorbed at the hBN/water interface. The hydronium, hydrogen, boron, nitrogen and oxygen atoms are respectively represented in yellow, white, blue, green and red.

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Comtet, J., Grosjean, B., Glushkov, E. et al. Direct observation of water-mediated single-proton transport between hBN surface defects. Nat. Nanotechnol. 15, 598–604 (2020). https://doi.org/10.1038/s41565-020-0695-4

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