RESUMO
The structure of electric double layers (EDLs) is crucial for all types of electrochemical processes. While in dilute solutions EDL structure can be approximately treated within the Gouy-Chapman-Stern regime, in highly ionic electrolytes the description of EDL has been largely elusive. Here we study the EDL structure of an ionic liquid on a series of crystalline electrodes. Through molecular dynamics (MD) simulations, we observe strong intermolecular interaction among cations and anions and propose that the cation-anion association structure at the innermost layer is a key descriptor of the EDL. Using our recently developed electrochemical 3D atomic force microscopy (EC-3D-AFM) technique, we confirm the theoretical prediction and further find that the width of the first EDL is an experimental gauge of the ion association structure in that layer. We expect such ion association descriptors to be broadly applicable to a large range of highly ionic electrolytes on various electrode surfaces.
RESUMO
The molecular structure of electric double layers (EDLs) at electrode-electrolyte interfaces is crucial for all types of electrochemical processes. Here, we probe the EDL structure of an ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPy-TFSI), using electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy. We extract the position and intensity of individual peaks corresponding to either intra- or inter-molecular vibrational modes and examine their dependence on the electrode potential. The observed trends suggest that the molecular reconfiguration mechanism is distinct between cations and anions. BMPy+ is found to always adsorb on the Au electrode surface via the pyrrolidinium ring while the alkyl chains strongly change their orientation at different potentials. In contrast, TFSI- is observed to have pronounced position shifts but negligible orientation changes as we sweep the electrode potential. Despite their distinct reconfiguration mechanisms, BMPy+ and TFSI- in the EDL are likely paired together through strong intermolecular interaction.
RESUMO
Electrochemical sensors, with high accuracy, good selectivity, and linear response, have been widely used for environmental protection, health monitoring, and disease treatment. However, to date, these sensors still have limit sensitivity or otherwise require the use of high-cost materials such as noble metals and enzymes. Here, we report a novel electrochemical sensor using a topological insulator, Bi2Te3. Through liquid-phase exfoliation, we prepared nano- and microflakes of Bi2Te3 and measured their performance in hydrogen peroxide sensing via electrocatalytic reduction processes. Our devices exhibit a sensitivity of â¼4900 µA mM-1 cm-2 and a detection limit of â¼10-8 molar, both of which are superior to typical noble metal-based electrochemical sensors. Through electrochemical analysis and microkinetic simulations, we extracted the kinetic parameters and gained insights into the reaction mechanism. We attribute the ultrahigh sensitivity to the facile electron transfer at the Bi2Te3-aqueous solution interface.
