Electrochemical Impedance Spectroscopy in a Droplet of Solution for the Investigation of Liquid/Solid Interface
Abstract
The local electrochemical behavior of a solid−
liquid interface can be studied by electrochemical impedance
spectroscopy (EIS). The investigated surface area can be
delimited by adding a drop of solution, which forms an
interface between the liquid drop and the working electrode,
and performing the measurements inside. The size of the drop
must be sufficiently small for a simultaneous wettability
characterization (from the contact angle measurement) and
appropriately large so that wettability is not influenced by the
presence of the working and the counter electrode inserted in
the droplet. In this work, we showed that EIS measurements
can be performed in a solution droplet of 2 to 4 μL, although
the electrochemical cell lacks the usual geometry. For our
measurements, we studied a model system consisting of a KCl aqueous solution of [Fe(CN)6]3−/4− redox couple at a Pt
electrode. All the results were compared with those obtained for a bulk configuration. The sessile drop configuration and the EIS
response were modeled using finite element method for different electrode sizes and configurations to account for
electrochemical kinetics and both current and potential distributions.