Dynamics of Collisions and Adsorption in the Stochastic Electrochemistry of Emulsion Microdroplets.
Anal Chem
; 93(22): 7993-8001, 2021 Jun 08.
Article
em En
| MEDLINE
| ID: mdl-34043322
Current-time recordings of emulsified toluene microdroplets containing 20 mM Ferrocene (Fc), show electrochemical oxidation peaks from individual adsorption events on disk microelectrodes (5 µm diameter). The average droplet diameter (â¼0.7 µm) determined from peak area integration was close to Dynamic Light Scattering measurements (â¼1 µm). Random walk simulations were performed deriving equations for droplet electrolysis using the diffusion and thermal velocity expressions from Einstein. The simulations show that multiple droplet-electrode collisions, lasting â¼0.11 µs each, occur before a droplet wanders away. Updating the Fc-concentration at every collision shows that a droplet only oxidizes â¼0.58% of its content in one collisional journey. In fact, it would take â¼5.45 × 106 collisions and â¼1.26 h to electrolyze the Fc in one droplet with the collision frequency derived from the thermal velocity (â¼0.52 cm/s) of a 1 µm-droplet. To simulate adsorption, the droplet was immobilized at first contact with the electrode while the electrolysis current was computed. This approach along with modeling of instrumental filtering, produced the best match of experimental peaks, which were attributed to electrolysis from single adsorption events instead of multiple consecutive collisions. These results point to a heightened sensitivity and speed when relying on adsorption instead of collisions. The electrochemical current for the former is limited by the probability of adsorption per collision, whereas for the latter, the current depends on the collision frequency and the probability of electron transfer per collision (J. Am. Chem. Soc. 2017, 139, 16923-16931).
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01-internacional
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MEDLINE
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En
Ano de publicação:
2021
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Article