Researchers from Utrecht University and Wetsus (Leeuwarden) have developed a new method to shed light on the so-called electrochemical double layer. This double layer forms whenever a charged solid surface interacts with a saline solution, such as on the electrodes in batteries, but also on the surface of small biological particles in living organisms. The resulting charge distribution crucially determines the stability of paint and food, the interactions between biological molecules, and the functioning of modern ‘supercapacitive’ energy storing devices. The results are published today in the prestigious Physical Review Letters, where the article is highlighted as Editors' Suggestion.
The study was a collaboration between experimental chemists and theoretical physicists. Research leader Ben Erné explains: “Near the charged surface, there are relatively many salt ions with a charge opposite to the charge of the surface. Compared to the saline solution far from the surface, a local structure emerges, which should theoretically lead to a small amount of heat being released.” The researchers were able to measure this heat. “The heat effect on the surface is very small,” Erné continues, “but because we used porous carbon electrodes that have a football field of surface per teaspoon of material, the surface area was so large that we were able to measure the effect.”
The results allow for a comparison between the theoretical view of the electric double layer and brand new information: the amount of heat released, which had not previously been taken into account. Accurate measurements of the heat released in the formation of the double layer can allow the researchers to relate the relative importance of electrical attraction compared to diffusion. The developed method provides new information that can be used to falsify theoretical models for the double layer.