Credit: Leiden University.
The Gouy-Chapman theory describes what happens near an electrode when it is in contact with a salt solution, but it does not match reality. A new version is presented by researcher Kasinath Ojha, assistant professor and professor. The next generation of textbooks will look different.
One of the things you will see when you look at a fuel cell is a piece of metal. A piece of metal is in contact with a solution of salt. If you zoom in on the interface between the salt solution and the electrode, you would see a lot of interactions. There is a shortage of electrons at the surface. The charge attracts the ion from the salt solution. The electrical double layer is a structure of charges. The double layer changes if you change the device's voltage. The Gouy-Chapman theory shows how this charge is distributed.
Theory doesn't match reality.
The description does not match reality, as was discovered by Professor of Catalysis and Surface Chemistry, and researcher, and associate professor, and researcher, and researcher, and researcher, and researcher, and researcher, and researcher, and researcher, and researcher, and researcher, and researcher, and researcher David Grahame verified the theory in the 40s and 50s of the 20th century because it was more difficult to measure with solid metals. It turns out that the theory is not applicable to solid metals such as Platinum. An improved theory was presented by the research team.
There is no important quantity to be found.
The Gouy-Chapman theory can be used to predict the missing interactions in the double layer. The ion in the salt solution are not attracted when zero charge accumulates at the electrode. The potential of zero charge is what this is. An important quantity for scientists.
Ojha, the main author of the article, says that they do measurements in very salt solutions. You can expect to find the potential of zero charge when you make the concentration low. We were never able to reach that point in our measurements.
It is a moment.
Ojha had a 'brilliant idea' to lower the concentration of the salt solution by a factor of ten. It turned out to be a eureka moment because no one had ever done that before. The fact that we have to go to extremely low concentrations tells us that there are more ion in the double layer than theory predicts. The theory doesn't take into account something that causes this amount of ion.
There are possible explanations.
The researchers don't know what's going on yet, but they have some ideas. The number of ion in the double layer does not matter. The size of the positively charged ion is different from the negatively charged ion. The smaller ion can get closer to the electrode than the larger one, which causes the measurement to be asymmetrical. Ohja noted that the interaction is sensitive to temperature changes.
The explanation cannot be chemical in nature, according to Koper. The professor received an Advanced Grant from the ERC in April of 2021.
Textbooks have been updated.
The Gouy-Chapman theory has been updated in a way that it describes and predicts reality more correctly. Ojha hopes that the findings will be used in the next generation of textbooks. With the updated theory, people can improve their understanding of the mechanisms and reactions at these kinds of metals.
The Double-layer structure of the Pt(111)–aqueous electrolyte interface was described in the Proceedings of the National Academy of Sciences. 10.1073/pnas.2116016
The National Academy of Sciences has a journal.
The century-old electrochemistry law got an update on January 20.
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