Insulating materials can in principle be made metallic by applying pressure. In the case of pure water, this is estimated1 to require a pressure of 48 megabar, which is beyond current experimental capabilities and may only exist in the interior of large planets or stars2,3,4. Indeed, recent estimates and experiments indicate that water at pressures accessible in the laboratory will at best be superionic with high protonic conductivity5, but not metallic with conductive electrons1. Here we show that a metallic water solution can be prepared by massive doping with electrons upon reacting water with alkali metals. Although analogous metallic solutions of liquid ammonia with high concentrations of solvated electrons have long been known and characterized6,7,8,9, the explosive interaction between alkali metals and water10,11 has so far only permitted the preparation of aqueous solutions with low, submetallic electron concentrations12,13,14. We found that the explosive behaviour of the water–alkali metal reaction can be suppressed by adsorbing water vapour at a low pressure of about 10−4 millibar onto liquid sodium–potassium alloy drops ejected into a vacuum chamber. This set-up leads to the formation of a transient gold-coloured layer of a metallic water solution covering the metal alloy drops. The metallic character of this layer, doped with around 5 × 1021 electrons per cubic centimetre, is confirmed using optical reflection and synchrotron X-ray photoelectron spectroscopies.
Your institute does not have access to this article
Subscribe to Nature+
Get immediate online access to the entire Nature family of 50+ journals
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Get time limited or full article access on ReadCube.
All prices are NET prices.
The datasets generated during the current study are available as Source Data or are available from the corresponding author upon reasonable request. Source data are provided with this paper.
Data-processing and fitting results can be generated using numerical methods described in Methods and Supplementary Information and developed computer codes that are available from the corresponding author upon reasonable request.
Hermann, A., Ashcroft, N. W. & Hoffmann, R. High pressure ices. Proc. Natl Acad. Sci. USA 109, 745–750 (2012).
Dubrovinsky, L., Dubrovinskaia, N., Prakapenka, V. B. & Abakumov, A. M. Implementation of micro-ball nanodiamond anvils for high-pressure studies above 6 Mbar. Nat. Commun. 3, 1163 (2012).
Cavazzoni, C. et al. Superionic and metallic states of water and ammonia at giant planet conditions. Science 283, 44–46 (1999).
Mattsson, T. R. & Desjarlais, M. P. Phase diagram and electrical conductivity of high energy-density water from density functional theory. Phys. Rev. Lett. 97, 017801 (2006).
Millot, M. et al. Nanosecond X-ray diffraction of shock-compressed superionic water ice. Nature 569, 251–255 (2019).
Zurek, E., Edwards, P. P. & Hoffmann, R. A molecular perspective on lithium-ammonia solutions. Angew. Chem. Int. Ed. 48, 8198–8232 (2009).
Thompson, J. C. Electrons in Liquid Ammonia (Clarendon Press, 1976).
Lodge, M. et al. Multielement NMR studies of the liquid-liquid phase separation and the metal-to-nonmetal transition in fluid lithium- and sodium-ammonia solutions. J. Phys. Chem. B 117, 13322–13334 (2013).
Buttersack, T. et al. Photoelectron spectra of alkali metal-ammonia microjets: from blue electrolyte to bronze metal. Science 368, 1086–1091 (2020).
Hutton, A. T. Dramatic demonstration for a large audience: the formation of hydroxyl ions in the reaction of sodium with water. J. Chem. Educ. 58, 506 (1981).
Mason, P. E. et al. Coulomb explosion during the early stages of the reaction of alkali metals with water. Nat. Chem. 7, 250–254 (2015).
Young, R. M. & Neumark, D. M. Dynamics of solvated electrons in clusters. Chem. Rev. 112, 5553–5577 (2012).
Mason, P. E., Buttersack, T., Bauerecker, S. & Jungwirth, P. A non-exploding alkali metal drop on water: from blue solvated electrons to bursting molten hydroxide. Angew. Chem. Int. Ed. 55, 13019–13022 (2016).
Suzuki, T. Ultrafast photoelectron spectroscopy of aqueous solutions. J. Chem. Phys. 151, 090901 (2019).
Alchagirov, B. B. et al. Surface tension and adsorption of components in the sodium–potassium alloy systems: effective liquid metal coolants promising in nuclear and space power engineering. Inorg. Mater. Appl. Res. 2, 461–467 (2011).
Addison, C. C. The Chemistry of Liquid Alkali Metals (Wiley, 1984).
Citrin, P. H. High-resolution X-ray photoemission from sodium metal and its hydroxide. Phys. Rev. B 8, 5545–5556 (1973).
Lueth, H. Surfaces and Interfaces of Solid Materials (Springer, 1997).
Kiskinova, M., Pirug, G. & Bonzel, H. P. Adsorption and decomposition of H2O on a K-covered Pt(111) surface. Surf. Sci. 150, 319–338 (1985).
Blass, P. M., Zhou, X. L. & White, J. M. Coadsorption and reaction of water and potassium on Ag(111). J. Phys. Chem. 94, 3054–3062 (1990).
Nachtrieb, N. H. Self-diffusion in liquid metals. Adv. Phys. 16, 309–323 (1967).
Ketteler, G. et al. The nature of water nucleation sites on TiO2(110) surfaces revealed by ambient pressure X-ray photoelectron spectroscopy. J. Phys. Chem. C 111, 8278–8282 (2007).
Kittel, C. Introduction to Solid State Physics (Wiley, 2005).
Abelès, F., Borensztein, Y., Decrescenzi, M. & Lopezrios, T. Optical evidence for longitudinal-waves in very thin Ag layers. Surf. Sci. 101, 123–130 (1980).
Winter, B., Faubel, M., Vacha, R. & Jungwirth, P. Behavior of hydroxide at the water/vapor interface. Chem. Phys. Lett. 474, 241–247 (2009).
Bonzel, H. P., Pirug, G. & Winkler, A. Adsorption of H2O on potassium films. Surf. Sci. 175, 287–312 (1986).
Hart, E. J. & Boag, J. W. Absorption spectrum of hydrated electron in water and in aqueous solutions. J. Am. Chem. Soc. 84, 4090–4095 (1962).
Barzynski, H. & Schulte-Frohlinde, D. On the nature of the electron traps in alkaline ice. Z. Naturforsch. A 22, 2131–2132 (1967).
Kevan, L. Slovated electron structure in glassy matrices. Acc. Chem. Res. 14, 138–145 (1981).
Buttersack, T. et al. Deeply cooled and temperature controlled microjets: liquid ammonia solutions released into vacuum for analysis by photoelectron spectroscopy. Rev. Sci. Instrum. 91, 043101 (2020).
Seidel, R., Pohl, M. N., Ali, H., Winter, B. & Aziz, E. F. Advances in liquid phase soft-X-ray photoemission spectroscopy: a new experimental setup at BESSY II. Rev. Sci. Instrum. 88, 073107 (2017).
Sawhney, K. J. S., Senf, F. & Gudat, W. PGM beamline with constant energy resolution mode for U49-2 undulator at BESSY-II. Nucl. Instrum. Methods Phys. Res. Sect. A 467, 466–469 (2001).
P.J. acknowledges support from the European Regional Development Fund (project ChemBioDrug number CZ.02.1.01/0.0/0.0/16_019/0000729). D.M.N. and C.L. acknowledge support from the Director of the Office of Basic Energy Science, Chemical Sciences Division of the US Department of Energy under contract number DE-AC02-05CH11231. D.M.N., C.L. and P.J. thank the Alexander von Humboldt Foundation for support. S.E.B., T.B. and R.S.M. are supported by the US National Science Foundation (CHE-1665532). P.E.M. acknowledges support from the viewers of his YouTube popular science channel. M.V. acknowledges support from the Charles University in Prague and from the International Max Planck Research School in Dresden. S.T. acknowledges support from JSPS KAKENHI grant number JP18K14178. R.S. acknowledges the German Research Foundation (DFG) for an Emmy-Noether Young-Investigator stipend (DFG, project SE 2253/3-1). F.T. and B.W. acknowledge support from the MaxWater initiative of the Max-Planck-Gesellschaft. All authors thank the staff of the Helmholtz-Zentrum Berlin for their support during the beamtime at BESSY II.
The authors declare no competing interests.
Peer review information Nature thanks Christoph Salzmann and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
This Supplementary Information file contains the following sections: (1) Sample preparation and employment in the experimental setup; (2) Photoelectron spectroscopy measurements; (3) Photoelectron spectra of pure NaK jets versus drops; (4) Photoelectron spectra of water vapour adsorbing on the NaK drop surface; (5) Data-analysis of photoelectron spectra acquired in fixed-mode operation; (6) Data-fitting of photoelectron spectra; (7) Optical reflection spectroscopy; and (8) Supplementary References
A detailed description of the experimental setup and conduction of the experiments.
About this article
Cite this article
Mason, P.E., Schewe, H.C., Buttersack, T. et al. Spectroscopic evidence for a gold-coloured metallic water solution. Nature 595, 673–676 (2021). https://doi.org/10.1038/s41586-021-03646-5