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Elektrochemische Doppelschichten in Nanostrukturen

Fachliche Zuordnung Theoretische Chemie: Moleküle, Materialien, Oberflächen
Physikalische Chemie von Molekülen, Flüssigkeiten und Grenzflächen, Biophysikalische Chemie
Förderung Förderung von 2015 bis 2021
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 284363025
 
Erstellungsjahr 2022

Zusammenfassung der Projektergebnisse

During the last decades electrochemistry has turned to the study of nanostructures, which promise interesting applications in batteries and so-called supercapacitors. Important examples for such structures are carbon nanotubes and graphene, which can be used as electrodes. When they are brought in contact with an electrolyte solution, the electrodes can be charged, and a countercharge forms in the solution, so that in total there is a double-layer of charges. The macroscopic theories that electrochemistry has developed for such double-layers do not hold at nanoscopic dimensions. When we entered the field, there were quite a number of articles on this topic, but none based on quantum-chemical calculations. It occurred to us that sufficiently small structures could be treated by an approximate method called density functional theory (DFT). Test calculations for ions in at near narrow carbon and gold nanotubes gave good results, so we embarked on the project. In the first part we had focused on the interaction of ions inside a tube with the tube itself, and between pairs of ions inside. On the basis of the understanding that we gained, we performed Maonte-Carlo simulations for the charging of nanotubes and nanoslits. In the second part we focused on an unexpected effect: The apparent attraction between ions of the same charge, one situated inside, the other outside a carbon tube – an apparent violation of Coulomb’s Law. We investigated three pairs of ions: Li-Li, Li-Cl. and Cl-Cl; in each case we found an effective attraction between the ions. In all cases the direct Coulomb interaction was small and effectively screened by the carbon tube. We could explain this effect by considering the response of the nanotubes to the presence of the ions, but for each pair the explanation was slightly different. This attraction was observed both for conducting and semiconducting nanotubes. It reminds of the formation of Cooper pairs in the theory of superconductivity, where the attraction is also caused the the lattice of the superconductor. We believe that we have discovered an important, fundamental effect for the interaction of ions with carbon nanostructures, which is also relevant for modelling Li-ion batteries. This research was supplemeted by Monte Carlo simulations for the capacity of nanoslits, and consideration for the effect of ion insertion on simple electron transfer reactions. On the basis of our research we published 5 articles in renounced international journals, one student obtained her Ph.D. The project involved cooperation with colleagues from Argentina, Russia, and the USA.

Projektbezogene Publikationen (Auswahl)

 
 

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