Candidate
Mahdi Yavarian | Applied Mathematics, University of Waterloo
Title
Modeling of Charging Dynamics in Electrochemical Systems with a Graphene Electrode
Abstract
Among the different electrochemical techniques available, electrochemical impedance spectroscopy (EIS) has led to a significant increase in studies ranging from energy storage purposes to biological applications such as biosensors and immunosensors. EIS is ideally suited for analysis of the various processes taking place at the electrode interface in response to the application of a small amplitude stimulus to the interface, taking advantage of frequency- resolved measurements performed when the electrochemical system is under a steady-state condition. By varying the frequency of the applied perturbation, it is possible to isolate the different timescales specific to each elementary step of a global mechanism, including double-layer charging, electrochemical charge transfer, mass transport, and adsorption at the interface of the electrode-electrolyte.
To develop strategies for increased performance of an electrochemical cell, it is critical to understand the underlying mechanisms of the interfacial properties of the electrodes in con- tact with an electrolyte. Among the traditional electrodes such as metals, graphene-based electrodes have received much attention and have been found to be a potential electrode for electric double-layer capacitors because of their special electronic properties and, in particular, its quantum capacitance which is distinct from Maxwell’s geometric or classic/dielectric capacitance. The utilization of graphene as an electrode material has opened up a new field in electrochemistry with much improved performance and provided an opportunity to under- stand the fundamental processes in the electrochemical capacitive interfaces in the ongoing quest for label-free detection for a range of proteins and other organic macromolecules.
The objectives of the current research as the future projects are: (1) Modeling EIS of electrochemical cells in the presence of graphene electrode by solving the linearized Poisson- Nernst-Planck equations, both in aqueous solutions and in ionic liquids, where additional boundary conditions will be discussed for the modified Poisson equation. (2) Proposing an EIS model of electrochemical cells containing graphene electrode away from the neutrality point using the technique of matched asymptotic expansion. (3) Modeling the 1/f noise in the context of the EIS when graphene is used as an electrode which may arise, e.g., from the kinetics of protonation/deprotonation of an oxide surface in the electrolyte by the site- binding model, or from the kinetics of trapping/detrapping of graphene’s charge carriers in the nearby oxide modeled by a random telegraph signal. (4) Proposing microscopic models for the empirical concepts adopted in the area of EIS, such as Constant Phase Element related to the heterogeneity of graphene electrode. (5) Modelling the frequency response of graphene electrode when graphene possesses finite conductivity using the transmission line methodology.