The molecular structure of water has been revealed, at the interface of gold electrodes, in a new experiment conducted by the Lawrence Berkeley National Laboratory (Berkeley Lab). That organization is managed by the Department of Energy (DOE).
Water molecules were examined on a gold surface, as differing electrical charges were applied to the sample. These particles, at their most basic level, resemble a boomerang, with an atom of oxygen in the center, and a hydrogen atom at each "tip."
Molecules of a liquid next to a solid surface behave differently than those within the main body of the fluid. This interfacial layer is critical to molecular behavior in biology and material science applications. Electrical charges delivered through the solid surface can alter the behavior of the liquid, but examination of these changes has proven difficult for researchers studying the phenomenon.
"At an electrode surface, the build-up of electrical charge, driven by a potential difference (or voltage), produces a strong electric field that drives molecular rearrangements in the electrolyte next to the electrode," Miquel Salmeron from Berkeley Lab and UC Berkeley's Materials Science and Engineering Department, said.
Researchers were able to develop a technique which allowed them to study changes in the arrangement of the water molecules in the interfacial layer with a precision never achieved prior to this study.
The team utilized X-ray absorption spectroscopy (XAS), a proven method of studying the arrangement of molecules, is not usually effective in water, which absorbs the energy. Most XAS measurements are undertaken in a vacuum, but water will quickly dissipate under those harsh conditions. To overcome this problem, investigators designed a tiny, sealed container, holding a small sample of water. This holder was manufactured with a tiny window, allowing X-rays to pass inside, into the sample. Inside the container was a thin layer of gold, in close vicinity to the water. A tiny wire attached to the gold electrode allowed the team to measure when electrons were released from the sample, after the water was excited by X-rays.
Faradaic current, created by electrochemical reactions in the sample chamber, also had to be separated from the current received in the electrode from the X-ray-excited water. The solution to this problem was to fire the X-rays into the container in pulses. A computer was then able to subtract charges from electrochemical causes from the total signal, leaving behind just the charge from the sample under investigation.
Carbonic acid, the liquid form of carbon dioxide, is essential in biological systems, as well as in the environment. This new research could provide a wealth of information on the behavior of this chemical with wide-ranging effects.
Investigation of the behavior of water at the interface of a gold electrode was detailed in the journal Science.
