Pure water is not a good conductor of electricity. In fact, it is an electrical insulator. For example, to conduct electricity, water must contain dissolved salts, but the conductivity of the electrolyte is relatively low, several orders of magnitude lower than that of metals. Is it possible to produce water that conducts electricity like copper wire?
Scientists hypothesize that this may occur in the cores of large planets, where high pressure compresses water molecules to the point where their electron shells begin to overlap. At present, generating this kind of pressure on the earth exceeds the ability of human beings, so people think that in the foreseeable future, the preparation of metal water under terrestrial conditions is still an elusive goal. However, an international research team led by Pavel Jungwirth from the Prague IOCB has developed a new method in which they managed to produce metallic water underground conditions that lasted for a few seconds. Their article was recently published in the journal Nature.
The idea of using tremendous pressure to make metal from water is nothing new. In principle, it should be possible to compress water molecules to the point where their electron shells begin to overlap and form so-called conduction bands similar to metallic materials. The required pressure of 50 Mbar (approximately 50 million times greater than the surface of the Earth) can be found in the core of a large planet, but we cannot yet achieve it under terrestrial conditions.
In collaboration with researchers from the University of Southern California, the Fritz Huber Institute, and other institutes, Jungwirth’s team recently developed a method that allows them to prepare metallic water by completely avoiding the need for high pressure. This method is based on previous research by Pavel Jungwirth Group, which focuses on the behavior of alkali metals in water and liquid ammonia. Inspired by alkali metal liquid ammonia solutions, which behave like metals at high concentrations, the researchers decided to try to create conduction bands, not by compressing water molecules, but by dissolving a large number of electrons released from them—alkali metals. However, in doing so, they must overcome a basic obstacle: As soon as they enter the water, the alkali metal will immediately explode.
“Throwing sodium into water is one of the most popular school experiments and the subject of many a YouTube video. As is well known, when you throw a chunk of sodium in water, you don’t get metallic water but an immediate and substantial explosion that takes out your apparatus,” says Jungwirth, who heads a group at IOCB Prague specializing in molecular modeling. “In order to contain this intense and, for laboratory purposes, rather counterproductive chemistry, we approached it the other way around; instead of adding the alkali metal to the water, we added the water to the metal.”
In the vacuum chamber, the researchers exposed a drop of sodium-potassium alloy to a small amount of water vapor, and the water vapor began to condense on its surface. The electrons released from the alkali metal dissolve in the surface water layer faster than the chemical reaction that causes the explosion. Their number is sufficient to exceed the critical limit for the formation of conduction bands to produce an aqueous metal solution, which, in addition to electrons, also contains dissolved alkali metal cations and chemically formed hydroxides and hydrogen.
“Thanks to this, we were able to create a thin layer of gold-colored metallic water solution that lasted for several seconds, and that was enough for us to not only see it with our own eyes but also measure it with spectrometers,” says Jungwirth, adding: “We more or less jury-rigged the necessary apparatus in a small lab at our institute in Prague, which is also where the first experiments took place. We then obtained the key evidence for the presence of metallic water using X-ray photoelectron spectroscopy on the synchrotron in Berlin.”
The research of IOCB Prague researchers and colleagues not only shows that metallic water can be prepared under terrestrial conditions but also provides a detailed characterization of the spectral characteristics associated with its beautiful golden metallic luster.