Speaker
Description
Pure, highly deionized, water is an electric insulator, and appreciable conductivity is only introduced via solvation of ions. However, even highly-concentrated, ionic aqueous solutions are far from exhibiting features of metallic systems, as their charge-carrier densities are orders of magnitude lower. Realizing a conductive / metallic state of water upon application of high pressure, as theorized in some studies, is not feasible given achievable pressures on Earth.[1] The situation is very different for ammonia, similarly a hydrogen-bonding liquid, where an insulator-to-metal transition occurs as a function of concentration of solvated electrons and di-electrons, typically provided by dissolving alkali metal.[2] But in water, solvated electrons are stable only for milliseconds. Even though the explosive nature of the reaction between alkali metals and water is high-school knowledge, its nature has been unraveled only very recently. Valence electrons of the alkali-metal surface are transferred to the aqueous solution almost instantly by Coulomb explosion, leading to a huge build-up of positive charges and the subsequent rapid deformation of the liquid alkali metal.[3]
Despite of this, we recently found an experimental procedure to stabilize alkali metal-water solutions, which can be observed for several seconds by naked eye and spectroscopically, showing the characteristic blue color of the solvated electrons.[4] In a follow-up experiment, we aimed at increasing the concentration of excess electrons in aqueous solution. This can be achieved by exposing water vapor to a drop of sodium-potassium alloy (NaK) in vacuum, which upon water condensation forms a thin shiny and golden layer on the drop surface. Both photoelectron and UV/Vis spectroscopy reveal a plasmon frequency of ~2.7 eV, evidencing the metallic nature (valence band) of this water solution.[5]
[1] A. Hermann, N. W. Ashcroft, R. Hoffmann; High pressure ices.
Proc. Natl. Acad. Sci. USA, 2012, 109, 745–750.
[2] T. Buttersack, P. E. Mason, R. S. McMullen, H. C. Schewe, T. Martinek, K. Brezina, M. Crhan, A. Gomez, D. Hein, G. Wartner, R. Seidel, H. Ali, S. Thürmer, O. Marsalek, B. Winter, S. E. Bradforth, and P. Jungwirth.
Science, 2020, 368, 1086-1091.
[3] P. E. Mason, F. Uhlig, V. Vanek, T. Buttersack, S. Bauerecker, and P. Jungwirth.
Nat. Chem., 2015, 7, 250-254.
[4] P. E. Mason, T. Buttersack, S. Bauerecker, and P. Jungwirth.
Angew. Chem. Int. Ed. Engl., 2016, 55, 13019-13022.
[5] P. E. Mason, H. C. Schewe, T. Buttersack, V. Kostal, M. Vitek, R. S. McMullen, H. Ali, F. Trinter, C. Lee, D. M. Neumark, S. Thürmer, R. Seidel, B. Winter, S. E. Bradforth, and P. Jungwirth.
Nature, 2021, 595, 673-676.
| Abstract Number (department-wise) | MP 17 |
|---|---|
| Department | MP (Meijer) |
