Electrochimie ultra-rapide : l'électrochimie à la nanoseconde!


Laure Fillaud, Emmanuel Maisonhaute

Cyclic voltammetry (CV) is the most often used technique in electrochemistry because it allows to visualize directly the reactivity of systems present or created in the solution or adsorbed at the electrode. The important parameter in CV is the scan rate ν because it allows to modulate the temporal resolution τ according to: τRT/(Fν).

Therefore, to access to fast kinetics, one seeks to increase ν. But what is the maximum scan rate that one can achieve? In practice, temporal resolution is limited by the ohmic drop and by the time constant of the electrochemical cell. To solve that issue, we use micrometric electrodes and a purposely home-made potentiostat. This allows to reach presently 2.5×106 Vs-1 whereas our experience with commercial systems shows that they fail to provide reliable results above 1000 Vs-1.

More specifically, we work in the field of molecular electronics, and the two examples presented below reflect our major activity:

Self-assembled monolayers


We measure the rate of electron transfer (k0) of a large number of systems, and more specifically of electroactive self-assembled monolayers. When the bridge between the redox center and the electrode is conjugated, electronic coupling is very efficient and ν of a few hundreds of kV.s-1 are required.

The figure presents the response in ultrafast CV in an electroactive osmium complex. When ν increases, the peaks shift from their low ν position, which allows to measure k0 according to Laviron's theory.





Cascades of electron transfers in supramolecular nanoobjects


dendriHere, increasing ν allows to explore electron hopping mechanisms inside very complex molecules such as dendrimers or giant rotaxanes that bear several redox centers. In collaboration with Jean-François Nierengarten's group (Strasbourg university), we evidenced the interactions between redox centers inside the same molecule, or between several molecules.

The figure presents a redox dendrimer and two CVs obtained onto a gold ultramicroelectrode modified with this dendrimer. When the scan rate increases, the peak shape is modified because only the the redox centers close to the electrode feel the electrochemical perturbation. The equivalent of a diffusion layer is then created, but inside the same molecule.




ANR FastGiant (2017-2021, N° ANR-17-CE07-0012-01)

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